Econstudentlog

Earth System Science

I decided not to rate this book. Some parts are great, some parts I didn’t think were very good.

I’ve added some quotes and links below. First a few links (I’ve tried not to add links here which I’ve also included in the quotes below):

Carbon cycle.
Origin of water on Earth.
Gaia hypothesis.
Albedo (climate and weather).
Snowball Earth.
Carbonate–silicate cycle.
Carbonate compensation depth.
Isotope fractionation.
CLAW hypothesis.
Mass-independent fractionation.
δ13C.
Great Oxygenation Event.
Acritarch.
Grypania.
Neoproterozoic.
Rodinia.
Sturtian glaciation.
Marinoan glaciation.
Ediacaran biota.
Cambrian explosion.
Quarternary.
Medieval Warm Period.
Little Ice Age.
Eutrophication.
Methane emissions.
Keeling curve.
CO2 fertilization effect.
Acid rain.
Ocean acidification.
Earth systems models.
Clausius–Clapeyron relation.
Thermohaline circulation.
Cryosphere.
The limits to growth.
Exoplanet Biosignature Gases.
Transiting Exoplanet Survey Satellite (TESS).
James Webb Space Telescope.
Habitable zone.
Kepler-186f.

A few quotes from the book:

“The scope of Earth system science is broad. It spans 4.5 billion years of Earth history, how the system functions now, projections of its future state, and ultimate fate. […] Earth system science is […] a deeply interdisciplinary field, which synthesizes elements of geology, biology, chemistry, physics, and mathematics. It is a young, integrative science that is part of a wider 21st-century intellectual trend towards trying to understand complex systems, and predict their behaviour. […] A key part of Earth system science is identifying the feedback loops in the Earth system and understanding the behaviour they can create. […] In systems thinking, the first step is usually to identify your system and its boundaries. […] what is part of the Earth system depends on the timescale being considered. […] The longer the timescale we look over, the more we need to include in the Earth system. […] for many Earth system scientists, the planet Earth is really comprised of two systems — the surface Earth system that supports life, and the great bulk of the inner Earth underneath. It is the thin layer of a system at the surface of the Earth […] that is the subject of this book.”

“Energy is in plentiful supply from the Sun, which drives the water cycle and also fuels the biosphere, via photosynthesis. However, the surface Earth system is nearly closed to materials, with only small inputs to the surface from the inner Earth. Thus, to support a flourishing biosphere, all the elements needed by life must be efficiently recycled within the Earth system. This in turn requires energy, to transform materials chemically and to move them physically around the planet. The resulting cycles of matter between the biosphere, atmosphere, ocean, land, and crust are called global biogeochemical cycles — because they involve biological, geological, and chemical processes. […] The global biogeochemical cycling of materials, fuelled by solar energy, has transformed the Earth system. […] It has made the Earth fundamentally different from its state before life and from its planetary neighbours, Mars and Venus. Through cycling the materials it needs, the Earth’s biosphere has bootstrapped itself into a much more productive state.”

“Each major element important for life has its own global biogeochemical cycle. However, every biogeochemical cycle can be conceptualized as a series of reservoirs (or ‘boxes’) of material connected by fluxes (or flows) of material between them. […] When a biogeochemical cycle is in steady state, the fluxes in and out of each reservoir must be in balance. This allows us to define additional useful quantities. Notably, the amount of material in a reservoir divided by the exchange flux with another reservoir gives the average ‘residence time’ of material in that reservoir with respect to the chosen process of exchange. For example, there are around 7 × 1016 moles of carbon dioxide (CO2) in today’s atmosphere, and photosynthesis removes around 9 × 1015 moles of CO2 per year, giving each molecule of CO2 a residence time of roughly eight years in the atmosphere before it is taken up, somewhere in the world, by photosynthesis. […] There are 3.8 × 1019 moles of molecular oxygen (O2) in today’s atmosphere, and oxidative weathering removes around 1 × 1013 moles of O2 per year, giving oxygen a residence time of around four million years with respect to removal by oxidative weathering. This makes the oxygen cycle […] a geological timescale cycle.”

“The water cycle is the physical circulation of water around the planet, between the ocean (where 97 per cent is stored), atmosphere, ice sheets, glaciers, sea-ice, freshwaters, and groundwater. […] To change the phase of water from solid to liquid or liquid to gas requires energy, which in the climate system comes from the Sun. Equally, when water condenses from gas to liquid or freezes from liquid to solid, energy is released. Solar heating drives evaporation from the ocean. This is responsible for supplying about 90 per cent of the water vapour to the atmosphere, with the other 10 per cent coming from evaporation on the land and freshwater surfaces (and sublimation of ice and snow directly to vapour). […] The water cycle is intimately connected to other biogeochemical cycles […]. Many compounds are soluble in water, and some react with water. This makes the ocean a key reservoir for several essential elements. It also means that rainwater can scavenge soluble gases and aerosols out of the atmosphere. When rainwater hits the land, the resulting solution can chemically weather rocks. Silicate weathering in turn helps keep the climate in a state where water is liquid.”

“In modern terms, plants acquire their carbon from carbon dioxide in the atmosphere, add electrons derived from water molecules to the carbon, and emit oxygen to the atmosphere as a waste product. […] In energy terms, global photosynthesis today captures about 130 terrawatts (1 TW = 1012 W) of solar energy in chemical form — about half of it in the ocean and about half on land. […] All the breakdown pathways for organic carbon together produce a flux of carbon dioxide back to the atmosphere that nearly balances photosynthetic uptake […] The surface recycling system is almost perfect, but a tiny fraction (about 0.1 per cent) of the organic carbon manufactured in photosynthesis escapes recycling and is buried in new sedimentary rocks. This organic carbon burial flux leaves an equivalent amount of oxygen gas behind in the atmosphere. Hence the burial of organic carbon represents the long-term source of oxygen to the atmosphere. […] the Earth’s crust has much more oxygen trapped in rocks in the form of oxidized iron and sulphur, than it has organic carbon. This tells us that there has been a net source of oxygen to the crust over Earth history, which must have come from the loss of hydrogen to space.”

“The oxygen cycle is relatively simple, because the reservoir of oxygen in the atmosphere is so massive that it dwarfs the reservoirs of organic carbon in vegetation, soils, and the ocean. Hence oxygen cannot get used up by the respiration or combustion of organic matter. Even the combustion of all known fossil fuel reserves can only put a small dent in the much larger reservoir of atmospheric oxygen (there are roughly 4 × 1017 moles of fossil fuel carbon, which is only about 1 per cent of the O2 reservoir). […] Unlike oxygen, the atmosphere is not the major surface reservoir of carbon. The amount of carbon in global vegetation is comparable to that in the atmosphere and the amount of carbon in soils (including permafrost) is roughly four times that in the atmosphere. Even these reservoirs are dwarfed by the ocean, which stores forty-five times as much carbon as the atmosphere, thanks to the fact that CO2 reacts with seawater. […] The exchange of carbon between the atmosphere and the land is largely biological, involving photosynthetic uptake and release by aerobic respiration (and, to a lesser extent, fires). […] Remarkably, when we look over Earth history there are fluctuations in the isotopic composition of carbonates, but no net drift up or down. This suggests that there has always been roughly one-fifth of carbon being buried in organic form and the other four-fifths as carbonate rocks. Thus, even on the early Earth, the biosphere was productive enough to support a healthy organic carbon burial flux.”

“The two most important nutrients for life are phosphorus and nitrogen, and they have very different biogeochemical cycles […] The largest reservoir of nitrogen is in the atmosphere, whereas the heavier phosphorus has no significant gaseous form. Phosphorus thus presents a greater recycling challenge for the biosphere. All phosphorus enters the surface Earth system from the chemical weathering of rocks on land […]. Phosphorus is concentrated in rocks in grains or veins of the mineral apatite. Natural selection has made plants on land and their fungal partners […] very effective at acquiring phosphorus from rocks, by manufacturing and secreting a range of organic acids that dissolve apatite. […] The average terrestrial ecosystem recycles phosphorus roughly fifty times before it is lost into freshwaters. […] The loss of phosphorus from the land is the ocean’s gain, providing the key input of this essential nutrient. Phosphorus is stored in the ocean as phosphate dissolved in the water. […] removal of phosphorus into the rock cycle balances the weathering of phosphorus from rocks on land. […] Although there is a large reservoir of nitrogen in the atmosphere, the molecules of nitrogen gas (N2) are extremely strongly bonded together, making nitrogen unavailable to most organisms. To split N2 and make nitrogen biologically available requires a remarkable biochemical feat — nitrogen fixation — which uses a lot of energy. In the ocean the dominant nitrogen fixers are cyanobacteria with a direct source of energy from sunlight. On land, various plants form a symbiotic partnership with nitrogen fixing bacteria, making a home for them in root nodules and supplying them with food in return for nitrogen. […] Nitrogen fixation and denitrification form the major input and output fluxes of nitrogen to both the land and the ocean, but there is also recycling of nitrogen within ecosystems. […] There is an intimate link between nutrient regulation and atmospheric oxygen regulation, because nutrient levels and marine productivity determine the source of oxygen via organic carbon burial. However, ocean nutrients are regulated on a much shorter timescale than atmospheric oxygen because their residence times are much shorter—about 2,000 years for nitrogen and 20,000 years for phosphorus.”

“[F]orests […] are vulnerable to increases in oxygen that increase the frequency and ferocity of fires. […] Combustion experiments show that fires only become self-sustaining in natural fuels when oxygen reaches around 17 per cent of the atmosphere. Yet for the last 370 million years there is a nearly continuous record of fossil charcoal, indicating that oxygen has never dropped below this level. At the same time, oxygen has never risen too high for fires to have prevented the slow regeneration of forests. The ease of combustion increases non-linearly with oxygen concentration, such that above 25–30 per cent oxygen (depending on the wetness of fuel) it is hard to see how forests could have survived. Thus oxygen has remained within 17–30 per cent of the atmosphere for at least the last 370 million years.”

“[T]he rate of silicate weathering increases with increasing CO2 and temperature. Thus, if something tends to increase CO2 or temperature it is counteracted by increased CO2 removal by silicate weathering. […] Plants are sensitive to variations in CO2 and temperature, and together with their fungal partners they greatly amplify weathering rates […] the most pronounced change in atmospheric CO2 over Phanerozoic time was due to plants colonizing the land. This started around 470 million years ago and escalated with the first forests 370 million years ago. The resulting acceleration of silicate weathering is estimated to have lowered the concentration of atmospheric CO2 by an order of magnitude […], and cooled the planet into a series of ice ages in the Carboniferous and Permian Periods.”

“The first photosynthesis was not the kind we are familiar with, which splits water and spits out oxygen as a waste product. Instead, early photosynthesis was ‘anoxygenic’ — meaning it didn’t produce oxygen. […] It could have used a range of compounds, in place of water, as a source of electrons with which to fix carbon from carbon dioxide and reduce it to sugars. Potential electron donors include hydrogen (H2) and hydrogen sulphide (H2S) in the atmosphere, or ferrous iron (Fe2+) dissolved in the ancient oceans. All of these are easier to extract electrons from than water. Hence they require fewer photons of sunlight and simpler photosynthetic machinery. The phylogenetic tree of life confirms that several forms of anoxygenic photosynthesis evolved very early on, long before oxygenic photosynthesis. […] If the early biosphere was fuelled by anoxygenic photosynthesis, plausibly based on hydrogen gas, then a key recycling process would have been the biological regeneration of this gas. Calculations suggest that once such recycling had evolved, the early biosphere might have achieved a global productivity up to 1 per cent of the modern marine biosphere. If early anoxygenic photosynthesis used the supply of reduced iron upwelling in the ocean, then its productivity would have been controlled by ocean circulation and might have reached 10 per cent of the modern marine biosphere. […] The innovation that supercharged the early biosphere was the origin of oxygenic photosynthesis using abundant water as an electron donor. This was not an easy process to evolve. To split water requires more energy — i.e. more high-energy photons of sunlight — than any of the earlier anoxygenic forms of photosynthesis. Evolution’s solution was to wire together two existing ‘photosystems’ in one cell and bolt on the front of them a remarkable piece of biochemical machinery that can rip apart water molecules. The result was the first cyanobacterial cell — the ancestor of all organisms performing oxygenic photosynthesis on the planet today. […] Once oxygenic photosynthesis had evolved, the productivity of the biosphere would no longer have been restricted by the supply of substrates for photosynthesis, as water and carbon dioxide were abundant. Instead, the availability of nutrients, notably nitrogen and phosphorus, would have become the major limiting factors on the productivity of the biosphere — as they still are today.” [If you’re curious to know more about how that fascinating ‘biochemical machinery’ works, this is a great book on these and related topics – US].

“On Earth, anoxygenic photosynthesis requires one photon per electron, whereas oxygenic photosynthesis requires two photons per electron. On Earth it took up to a billion years to evolve oxygenic photosynthesis, based on two photosystems that had already evolved independently in different types of anoxygenic photosynthesis. Around a fainter K- or M-type star […] oxygenic photosynthesis is estimated to require three or more photons per electron — and a corresponding number of photosystems — making it harder to evolve. […] However, fainter stars spend longer on the main sequence, giving more time for evolution to occur.”

“There was a lot more energy to go around in the post-oxidation world, because respiration of organic matter with oxygen yields an order of magnitude more energy than breaking food down anaerobically. […] The revolution in biological complexity culminated in the ‘Cambrian Explosion’ of animal diversity 540 to 515 million years ago, in which modern food webs were established in the ocean. […] Since then the most fundamental change in the Earth system has been the rise of plants on land […], beginning around 470 million years ago and culminating in the first global forests by 370 million years ago. This doubled global photosynthesis, increasing flows of materials. Accelerated chemical weathering of the land surface lowered atmospheric carbon dioxide levels and increased atmospheric oxygen levels, fully oxygenating the deep ocean. […] Although grasslands now cover about a third of the Earth’s productive land surface they are a geologically recent arrival. Grasses evolved amidst a trend of declining atmospheric carbon dioxide, and climate cooling and drying, over the past forty million years, and they only became widespread in two phases during the Miocene Epoch around seventeen and six million years ago. […] Since the rise of complex life, there have been several mass extinction events. […] whilst these rolls of the extinction dice marked profound changes in evolutionary winners and losers, they did not fundamentally alter the operation of the Earth system.” [If you’re interested in this kind of stuff, the evolution of food webs and so on, Herrera et al.’s wonderful book is a great place to start – US]

“The Industrial Revolution marks the transition from societies fuelled largely by recent solar energy (via biomass, water, and wind) to ones fuelled by concentrated ‘ancient sunlight’. Although coal had been used in small amounts for millennia, for example for iron making in ancient China, fossil fuel use only took off with the invention and refinement of the steam engine. […] With the Industrial Revolution, food and biomass have ceased to be the main source of energy for human societies. Instead the energy contained in annual food production, which supports today’s population, is at fifty exajoules (1 EJ = 1018 joules), only about a tenth of the total energy input to human societies of 500 EJ/yr. This in turn is equivalent to about a tenth of the energy captured globally by photosynthesis. […] solar energy is not very efficiently converted by photosynthesis, which is 1–2 per cent efficient at best. […] The amount of sunlight reaching the Earth’s land surface (2.5 × 1016 W) dwarfs current total human power consumption (1.5 × 1013 W) by more than a factor of a thousand.”

“The Earth system’s primary energy source is sunlight, which the biosphere converts and stores as chemical energy. The energy-capture devices — photosynthesizing organisms — construct themselves out of carbon dioxide, nutrients, and a host of trace elements taken up from their surroundings. Inputs of these elements and compounds from the solid Earth system to the surface Earth system are modest. Some photosynthesizers have evolved to increase the inputs of the materials they need — for example, by fixing nitrogen from the atmosphere and selectively weathering phosphorus out of rocks. Even more importantly, other heterotrophic organisms have evolved that recycle the materials that the photosynthesizers need (often as a by-product of consuming some of the chemical energy originally captured in photosynthesis). This extraordinary recycling system is the primary mechanism by which the biosphere maintains a high level of energy capture (productivity).”

“[L]ike all stars on the ‘main sequence’ (which generate energy through the nuclear fusion of hydrogen into helium), the Sun is burning inexorably brighter with time — roughly 1 per cent brighter every 100 million years — and eventually this will overheat the planet. […] Over Earth history, the silicate weathering negative feedback mechanism has counteracted the steady brightening of the Sun by removing carbon dioxide from the atmosphere. However, this cooling mechanism is near the limits of its operation, because CO2 has fallen to limiting levels for the majority of plants, which are key amplifiers of silicate weathering. Although a subset of plants have evolved which can photosynthesize down to lower CO2 levels [the author does not go further into this topic, but here’s a relevant link – US], they cannot draw CO2 down lower than about 10 ppm. This means there is a second possible fate for life — running out of CO2. Early models projected either CO2 starvation or overheating […] occurring about a billion years in the future. […] Whilst this sounds comfortingly distant, it represents a much shorter future lifespan for the Earth’s biosphere than its past history. Earth’s biosphere is entering its old age.”

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September 28, 2017 Posted by | Astronomy, Biology, Books, Botany, Chemistry, Geology, Paleontology, Physics | Leave a comment

Magnetism

This book was ‘okay…ish’, but I must admit I was a bit disappointed; the coverage was much too superficial, and I’m reasonably sure the lack of formalism made the coverage harder for me to follow than it could have been. I gave the book two stars on goodreads.

Some quotes and links below.

Quotes:

“In the 19th century, the principles were established on which the modern electromagnetic world could be built. The electrical turbine is the industrialized embodiment of Faraday’s idea of producing electricity by rotating magnets. The turbine can be driven by the wind or by falling water in hydroelectric power stations; it can be powered by steam which is itself produced by boiling water using the heat produced from nuclear fission or burning coal or gas. Whatever the method, rotating magnets inducing currents feed the appetite of the world’s cities for electricity, lighting our streets, powering our televisions and computers, and providing us with an abundant source of energy. […] rotating magnets are the engine of the modern world. […] Modern society is built on the widespread availability of cheap electrical power, and almost all of it comes from magnets whirling around in turbines, producing electric current by the laws discovered by Oersted, Ampère, and Faraday.”

“Maxwell was the first person to really understand that a beam of light consists of electric and magnetic oscillations propagating together. The electric oscillation is in one plane, at right angles to the magnetic oscillation. Both of them are in directions at right angles to the direction of propagation. […] The oscillations of electricity and magnetism in a beam of light are governed by Maxwell’s four beautiful equations […] Above all, Einstein’s work on relativity was motivated by a desire to preserve the integrity of Maxwell’s equations at all costs. The problem was this: Maxwell had derived a beautiful expression for the speed of light, but the speed of light with respect to whom? […] Einstein deduced that the way to fix this would be to say that all observers will measure the speed of any beam of light to be the same. […] Einstein showed that magnetism is a purely relativistic effect, something that wouldn’t even be there without relativity. Magnetism is an example of relativity in everyday life. […] Magnetic fields are what electric fields look like when you are moving with respect to the charges that ‘cause’ them. […] every time a magnetic field appears in nature, it is because a charge is moving with respect to the observer. Charge flows down a wire to make an electric current and this produces magnetic field. Electrons orbit an atom and this ‘orbital’ motion produces a magnetic field. […] the magnetism of the Earth is due to electrical currents deep inside the planet. Motion is the key in each and every case, and magnetic fields are the evidence that charge is on the move. […] Einstein’s theory of relativity casts magnetism in a new light. Magnetic fields are a relativistic correction which you observe when charges move relative to you.”

“[T]he Bohr–van Leeuwen theorem […] states that if you assume nothing more than classical physics, and then go on to model a material as a system of electrical charges, then you can show that the system can have no net magnetization; in other words, it will not be magnetic. Simply put, there are no lodestones in a purely classical Universe. This should have been a revolutionary and astonishing result, but it wasn’t, principally because it came about 20 years too late to knock everyone’s socks off. By 1921, the initial premise of the Bohr–van Leeuwen theorem, the correctness of classical physics, was known to be wrong […] But when you think about it now, the Bohr–van Leeuwen theorem gives an extraordinary demonstration of the failure of classical physics. Just by sticking a magnet to the door of your refrigerator, you have demonstrated that the Universe is not governed by classical physics.”

“[M]ost real substances are weakly diamagnetic, meaning that when placed in a magnetic field they become weakly magnetic in the opposite direction to the field. Water does this, and since animals are mostly water, it applies to them. This is the basis of Andre Geim’s levitating frog experiment: a live frog is placed in a strong magnetic field and because of its diamagnetism it becomes weakly magnetic. In the experiment, a non-uniformity of the magnetic field induces a force on the frog’s induced magnetism and, hey presto, the frog levitates in mid-air.”

“In a conventional hard disk technology, the disk needs to be spun very fast, around 7,000 revolutions per minute. […] The read head floats on a cushion of air about 15 nanometres […] above the surface of the rotating disk, reading bits off the disk at tens of megabytes per second. This is an extraordinary engineering achievement when you think about it. If you were to scale up a hard disk so that the disk is a few kilometres in diameter rather a few centimetres, then the read head would be around the size of the White House and would be floating over the surface of the disk on a cushion of air one millimetre thick (the diameter of the head of a pin) while the disk rotated below it at a speed of several million miles per hour (fast enough to go round the equator a couple of dozen times in a second). On this scale, the bits would be spaced a few centimetres apart around each track. Hard disk drives are remarkable. […] Although hard disks store an astonishing amount of information and are cheap to manufacture, they are not fast information retrieval systems. To access a particular piece of information involves moving the head and rotating the disk to a particular spot, taking perhaps a few milliseconds. This sounds quite rapid, but with processors buzzing away and performing operations every nanosecond or so, a few milliseconds is glacial in comparison. For this reason, modern computers often use solid state memory to store temporary information, reserving the hard disk for longer-term bulk storage. However, there is a trade-off between cost and performance.”

“In general, there is a strong economic drive to store more and more information in a smaller and smaller space, and hence a need to find a way to make smaller and smaller bits. […] [However] greater miniturization comes at a price. The point is the following: when you try to store a bit of information in a magnetic medium, an important constraint on the usefulness of the technology is how long the information will last for. Almost always the information is being stored at room temperature and so needs to be robust to the ever present random jiggling effects produced by temperature […] It turns out that the crucial parameter controlling this robustness is the ratio of the energy needed to reverse the bit of information (in other words, the energy required to change the magnetization from one direction to the reverse direction) to a characteristic energy associated with room temperature (an energy which is, expressed in electrical units, approximately one-fortieth of a Volt). So if the energy to flip a magnetic bit is very large, the information can persist for thousands of years […] while if it is very small, the information might only last for a small fraction of a second […] This energy is proportional to the volume of the magnetic bit, and so one immediately sees a problem with making bits smaller and smaller: though you can store bits of information at higher density, there is a very real possibility that the information might be very rapidly scrambled by thermal fluctuations. This motivates the search for materials in which it is very hard to flip the magnetization from one state to the other.”

“The change in the Earth’s magnetic field over time is a fairly noticeable phenomenon. Every decade or so, compass needles in Africa are shifting by a degree, and the magnetic field overall on planet Earth is about 10% weaker than it was in the 19th century.”

Below I have added some links to topics and people covered/mentioned in the book. Many of the links below have likely also been included in some of the other posts about books from the A Brief Introduction OUP physics series which I’ve posted this year – the main point of adding these links is to give some idea what kind of stuff’s covered in the book:

Magnetism.
Magnetite.
Lodestone.
William Gilbert/De Magnete.
Alessandro Volta.
Ampère’s circuital law.
Charles-Augustin de Coulomb.
Hans Christian Ørsted.
Leyden jar
/voltaic cell/battery (electricity).
Solenoid.
Electromagnet.
Homopolar motor.
Michael Faraday.
Electromagnetic induction.
Dynamo.
Zeeman effect.
Alternating current/Direct current.
Nikola Tesla.
Thomas Edison.
Force field (physics).
Ole Rømer.
Centimetre–gram–second system of units.
James Clerk Maxwell.
Maxwell’s equations.
Permittivity.
Permeability (electromagnetism).
Gauss’ law.
Michelson–Morley experiment
.
Special relativity.
Drift velocity.
Curie’s law.
Curie temperature.
Andre Geim.
Diamagnetism.
Paramagnetism.
Exchange interaction.
Magnetic domain.
Domain wall (magnetism).
Stern–Gerlach experiment.
Dirac equation.
Giant magnetoresistance.
Spin valve.
Racetrack memory.
Perpendicular recording.
Bubble memory (“an example of a brilliant idea which never quite made it”, as the author puts it).
Single-molecule magnet.
Spintronics.
Earth’s magnetic field.
Aurora.
Van Allen radiation belt.
South Atlantic Anomaly.
Geomagnetic storm.
Geomagnetic reversal.
Magnetar.
ITER (‘International Thermonuclear Experimental Reactor’).
Antiferromagnetism.
Spin glass.
Quantum spin liquid.
Multiferroics.
Spin ice.
Magnetic monopole.
Ice rules.

August 28, 2017 Posted by | Books, Computer science, Geology, Physics | Leave a comment

The Antarctic

“A very poor book with poor coverage, mostly about politics and history (and a long collection of names of treaties and organizations). I would definitely not have finished it if it were much longer than it is.”

That was what I wrote about the book in my goodreads review. I was strongly debating whether or not to blog it at all, but I decided in the end to just settle for some very lazy coverage of the book, only consisting of links to content covered in the book. I only cover the book here to at least have some chance of remembering which kinds of things were covered in the book later on.

If you’re interested enough in the Antarctic to read a book about it, read Scott’s Last Expedition instead of this one (here’s my goodreads review of Scott).

Links:

Antarctica (featured).
Antarctic Convergence.
Antarctic Circle.
Southern Ocean.
Antarctic Circumpolar Current.
West Antarctic Ice Sheet.
East Antarctic Ice Sheet.
McMurdo Dry Valleys.
Notothenioidei.
Patagonian toothfish.
Antarctic krill.
Fabian Gottlieb von Bellingshausen.
Edward Bransfield.
James Clark Ross.
United States Exploring Expedition.
Heroic Age of Antarctic Exploration (featured).
Nimrod Expedition (featured).
Roald Amundsen.
Wilhelm Filchner.
Japanese Antarctic Expedition.
Terra Nova Expedition (featured).
Lincoln Ellsworth.
British Graham Land expedition.
German Antarctic Expedition (1938–1939).
Operation Highjump.
Operation Windmill.
Operation Deep Freeze.
Commonwealth Trans-Antarctic Expedition.
Caroline Mikkelsen.
International Association of Antarctica Tour Operators.
Territorial claims in Antarctica.
International Geophysical Year.
Antarctic Treaty System.
Operation Tabarin.
Scientific Committee on Antarctic Research.
United Nations Convention on the Law of the Sea.
Convention on the Continental Shelf.
Council of Managers of National Antarctic Programs.
British Antarctic Survey.
International Polar Year.
Antarctic ozone hole.
Gamburtsev Mountain Range.
Pine Island Glacier (‘good article’).
Census of Antarctic Marine Life.
Lake Ellsworth Consortium.
Antarctic fur seal.
Southern elephant seal.
Grytviken (whaling-related).
International Convention for the Regulation of Whaling.
International Whaling Commission.
Ocean Drilling Program.
Convention on the Regulation of Antarctic Mineral Resource Activities.
Agreement on the Conservation of Albatrosses and Petrels.

July 3, 2017 Posted by | Biology, Books, Geography, Geology, History, Wikipedia | Leave a comment

Rocks: A very short introduction

I liked the book. Below I have added some sample observations from the book, as well as a collection of links to various topics covered/mentioned in the book.

“To make a variety of rocks, there needs to be a variety of minerals. The Earth has shown a capacity for making an increasing variety of minerals throughout its existence. Life has helped in this [but] [e]ven a dead planet […] can evolve a fine array of minerals and rocks. This is done simply by stretching out the composition of the original homogeneous magma. […] Such stretching of composition would have happened as the magma ocean of the earliest […] Earth cooled and began to solidify at the surface, forming the first crust of this new planet — and the starting point, one might say, of our planet’s rock cycle. When magma cools sufficiently to start to solidify, the first crystals that form do not have the same composition as the overall magma. In a magma of ‘primordial Earth’ type, the first common mineral to form was probably olivine, an iron-and-magnesium-rich silicate. This is a dense mineral, and so it tends to sink. As a consequence the remaining magma becomes richer in elements such as calcium and aluminium. From this, at temperatures of around 1,000°C, the mineral plagioclase feldspar would then crystallize, in a calcium-rich variety termed anorthite. This mineral, being significantly less dense than olivine, would tend to rise to the top of the cooling magma. On the Moon, itself cooling and solidifying after its fiery birth, layers of anorthite crystals several kilometres thick built up as the rock — anorthosite — of that body’s primordial crust. This anorthosite now forms the Moon’s ancient highlands, subsequently pulverized by countless meteorite impacts. This rock type can be found on Earth, too, particularly within ancient terrains. […] Was the Earth’s first surface rock also anorthosite? Probably—but we do not know for sure, as the Earth, a thoroughly active planet throughout its existence, has consumed and obliterated nearly all of the crust that formed in the first several hundred million years of its existence, in a mysterious interval of time that we now call the Hadean Eon. […] The earliest rocks that we know of date from the succeeding Archean Eon.”

“Where plates are pulled apart, then pressure is released at depth, above the ever-opening tectonic rift, for instance beneath the mid-ocean ridge that runs down the centre of the Atlantic Ocean. The pressure release from this crustal stretching triggers decompression melting in the rocks at depth. These deep rocks — peridotite — are dense, being rich in the iron- and magnesium-bearing mineral olivine. Heated to the point at which melting just begins, so that the melt fraction makes up only a few percentage points of the total, those melt droplets are enriched in silica and aluminium relative to the original peridotite. The melt will have a composition such that, when it cools and crystallizes, it will largely be made up of crystals of plagioclase feldspar together with pyroxene. Add a little more silica and quartz begins to appear. With less silica, olivine crystallizes instead of quartz.

The resulting rock is basalt. If there was anything like a universal rock of rocky planet surfaces, it is basalt. On Earth it makes up almost all of the ocean floor bedrock — in other words, the ocean crust, that is, the surface layer, some 10 km thick. Below, there is a boundary called the Mohorovičič Discontinuity (or ‘Moho’ for short)[…]. The Moho separates the crust from the dense peridotitic mantle rock that makes up the bulk of the lithosphere. […] Basalt makes up most of the surface of Venus, Mercury, and Mars […]. On the Moon, the ‘mare’ (‘seas’) are not of water but of basalt. Basalt, or something like it, will certainly be present in large amounts on the surfaces of rocky exoplanets, once we are able to bring them into close enough focus to work out their geology. […] At any one time, ocean floor basalts are the most common rock type on our planet’s surface. But any individual piece of ocean floor is, geologically, only temporary. It is the fate of almost all ocean crust — islands, plateaux, and all — to be destroyed within ocean trenches, sliding down into the Earth along subduction zones, to be recycled within the mantle. From that destruction […] there arise the rocks that make up the most durable component of the Earth’s surface: the continents.”

“Basaltic magmas are a common starting point for many other kinds of igneous rocks, through the mechanism of fractional crystallization […]. Remove the early-formed crystals from the melt, and the remaining melt will evolve chemically, usually in the direction of increasing proportions of silica and aluminium, and decreasing amounts of iron and magnesium. These magmas will therefore produce intermediate rocks such as andesites and diorites in the finely and coarsely crystalline varieties, respectively; and then more evolved silica-rich rocks such as rhyolites (fine), microgranites (medium), and granites (coarse). […] Granites themselves can evolve a little further, especially at the late stages of crystallization of large bodies of granite magma. The final magmas are often water-rich ones that contain many of the incompatible elements (such as thorium, uranium, and lithium), so called because they are difficult to fit within the molecular frameworks of the common igneous minerals. From these final ‘sweated-out’ magmas there can crystallize a coarsely crystalline rock known as pegmatite — famous because it contains a wide variety of minerals (of the ~4,500 minerals officially recognized on Earth […] some 500 have been recognized in pegmatites).”

“The less oxygen there is [at the area of deposition], the more the organic matter is preserved into the rock record, and it is where the seawater itself, by the sea floor, has little or no oxygen that some of the great carbon stores form. As animals cannot live in these conditions, organic-rich mud can accumulate quietly and undisturbed, layer by layer, here and there entombing the skeleton of some larger planktonic organism that has fallen in from the sunlit, oxygenated waters high above. It is these kinds of sediments that […] generate[d] the oil and gas that currently power our civilization. […] If sedimentary layers have not been buried too deeply, they can remain as soft muds or loose sands for millions of years — sometimes even for hundreds of millions of years. However, most buried sedimentary layers, sooner or later, harden and turn into rock, under the combined effects of increasing heat and pressure (as they become buried ever deeper under subsequent layers of sediment) and of changes in chemical environment. […] As rocks become buried ever deeper, they become progressively changed. At some stage, they begin to change their character and depart from the condition of sedimentary strata. At this point, usually beginning several kilometres below the surface, buried igneous rocks begin to transform too. The process of metamorphism has started, and may progress until those original strata become quite unrecognizable.”

“Frozen water is a mineral, and this mineral can make up a rock, both on Earth and, very commonly, on distant planets, moons, and comets […]. On Earth today, there are large deposits of ice strata on the cold polar regions of Antarctica and Greenland, with smaller amounts in mountain glaciers […]. These ice strata, the compressed remains of annual snowfalls, have simply piled up, one above the other, over time; on Antarctica, they reach almost 5 km in thickness and at their base are about a million years old. […] The ice cannot pile up for ever, however: as the pressure builds up it begins to behave plastically and to slowly flow downslope, eventually melting or, on reaching the sea, breaking off as icebergs. As the ice mass moves, it scrapes away at the underlying rock and soil, shearing these together to form a mixed deposit of mud, sand, pebbles, and characteristic striated (ice-scratched) cobbles and boulders […] termed a glacial till. Glacial tills, if found in the ancient rock record (where, hardened, they are referred to as tillites), are a sure clue to the former presence of ice.”

“At first approximation, the mantle is made of solid rock and is not […] a seething mass of magma that the fragile crust threatens to founder into. This solidity is maintained despite temperatures that, towards the base of the mantle, are of the order of 3,000°C — temperatures that would very easily melt rock at the surface. It is the immense pressures deep in the Earth, increasing more or less in step with temperature, that keep the mantle rock in solid form. In more detail, the solid rock of the mantle may include greater or lesser (but usually lesser) amounts of melted material, which locally can gather to produce magma chambers […] Nevertheless, the mantle rock is not solid in the sense that we might imagine at the surface: it is mobile, and much of it is slowly moving plastically, taking long journeys that, over many millions of years, may encompass the entire thickness of the mantle (the kinds of speeds estimated are comparable to those at which tectonic plates move, of a few centimetres a year). These are the movements that drive plate tectonics and that, in turn, are driven by the variation in temperature (and therefore density) from the contact region with the hot core, to the cooler regions of the upper mantle.”

“The outer core will not transmit certain types of seismic waves, which indicates that it is molten. […] Even farther into the interior, at the heart of the Earth, this metal magma becomes rock once more, albeit a rock that is mostly crystalline iron and nickel. However, it was not always so. The core used to be liquid throughout and then, some time ago, it began to crystallize into iron-nickel rock. Quite when this happened has been widely debated, with estimates ranging from over three billion years ago to about half a billion years ago. The inner core has now grown to something like 2,400 km across. Even allowing for the huge spans of geological time involved, this implies estimated rates of solidification that are impressive in real time — of some thousands of tons of molten metal crystallizing into solid form per second.”

“Rocks are made out of minerals, and those minerals are not a constant of the universe. A little like biological organisms, they have evolved and diversified through time. As the minerals have evolved, so have the rocks that they make up. […] The pattern of evolution of minerals was vividly outlined by Robert Hazen and his colleagues in what is now a classic paper published in 2008. They noted that in the depths of outer space, interstellar dust, as analysed by the astronomers’ spectroscopes, seems to be built of only about a dozen minerals […] Their component elements were forged in supernova explosions, and these minerals condensed among the matter and radiation that streamed out from these stellar outbursts. […] the number of minerals on the new Earth [shortly after formation was] about 500 (while the smaller, largely dry Moon has about 350). Plate tectonics began, with its attendant processes of subduction, mountain building, and metamorphism. The number of minerals rose to about 1,500 on a planet that may still have been biologically dead. […] The origin and spread of life at first did little to increase the number of mineral species, but once oxygen-producing photosynthesis started, then there was a great leap in mineral diversity as, for each mineral, various forms of oxide and hydroxide could crystallize. After this step, about two and a half billion years ago, there were over 4,000 minerals, most of them vanishingly rare. Since then, there may have been a slight increase in their numbers, associated with such events as the appearance and radiation of metazoan animals and plants […] Humans have begun to modify the chemistry and mineralogy of the Earth’s surface, and this has included the manufacture of many new types of mineral. […] Human-made minerals are produced in laboratories and factories around the world, with many new forms appearing every year. […] Materials sciences databases now being compiled suggest that more than 50,000 solid, inorganic, crystalline species have been created in the laboratory.”

Some links of interest:

Rock. Presolar grains. Silicate minerals. Silicon–oxygen tetrahedron. Quartz. Olivine. Feldspar. Mica. Jean-Baptiste Biot. Meteoritics. Achondrite/Chondrite/Chondrule. Carbonaceous chondrite. Iron–nickel alloy. Widmanstätten pattern. Giant-impact hypothesis (in the book this is not framed as a hypothesis nor is it explicitly referred to as the GIH; it’s just taken to be the correct account of what happened back then – US). Alfred Wegener. Arthur Holmes. Plate tectonics. Lithosphere. Asthenosphere. Fractional Melting (couldn’t find a wiki link about this exact topic; the MIT link is quite technical – sorry). Hotspot (geology). Fractional crystallization. Metastability. Devitrification. Porphyry (geology). Phenocryst. Thin section. Neptunism. Pyroclastic flow. Ignimbrite. Pumice. Igneous rock. Sedimentary rock. Weathering. Slab (geology). Clay minerals. Conglomerate (geology). BrecciaAeolian processes. Hummocky cross-stratification. Ralph Alger Bagnold. Montmorillonite. Limestone. Ooid. Carbonate platform. Turbidite. Desert varnish. Evaporite. Law of Superposition. Stratigraphy. Pressure solution. Compaction (geology). Recrystallization (geology). Cleavage (geology). Phyllite. Aluminosilicate. Gneiss. Rock cycle. Ultramafic rock. Serpentinite. Pressure-Temperature-time paths. Hornfels. Impactite. Ophiolite. Xenolith. Kimberlite. Transition zone (Earth). Mantle convection. Mantle plume. Core–mantle boundary. Post-perovskite. Earth’s inner core. Inge Lehmann. Stromatolites. Banded iron formations. Microbial mat. Quorum sensing. Cambrian explosion. Bioturbation. Biostratigraphy. Coral reef. Radiolaria. Carbonate compensation depth. Paleosol. Bone bed. Coprolite. Allan Hills 84001. Tharsis. Pedestal crater. Mineraloid. Concrete.

February 19, 2017 Posted by | Biology, Books, Geology | Leave a comment

The Origin of Species

I figured I ought to blog this book at some point, and today I decided to take out the time to do it. This is the second book by Darwin I’ve read – for blog content dealing with Darwin’s book The Voyage of the Beagle, see these posts. The two books are somewhat different; Beagle is sort of a travel book written by a scientist who decided to write down his observations during his travels, whereas Origin is a sort of popular-science research treatise – for more details on Beagle, see the posts linked above. If you plan on reading both the way I did I think you should aim to read them in the order they are written.

I did not rate the book on goodreads because I could not think of a fair way to rate the book; it’s a unique and very important contribution to the history of science, but how do you weigh the other dimensions? I decided not to try. Some of the people reviewing the book on goodreads call the book ‘dry’ or ‘dense’, but I’d say that I found the book quite easy to read compared to quite a few of the other books I’ve been reading this year and it doesn’t actually take that long to read; thus I read a quite substantial proportion of the book during a one day trip to Copenhagen and back. The book can be read by most literate people living in the 21st century – you do not need to know any evolutionary biology to read this book – but that said, how you read the book will to some extent depend upon how much you know about the topics about which Darwin theorizes in his book. I had a conversation with my brother about the book a short while after I’d read it, and I recall noting during that conversation that in my opinion one would probably get more out of reading this book if one has at least some knowledge of geology (for example some knowledge about the history of the theory of continental drift – this book was written long before the theory of plate tectonics was developed), paleontology, Mendel’s laws/genetics/the modern synthesis and modern evolutionary thought, ecology and ethology, etc. Whether or not you actually do ‘get more out of the book’ if you already know some stuff about the topics about which Darwin speaks is perhaps an open question, but I think a case can certainly be made that someone who already knows a bit about evolution and related topics will read this book in a different manner than will someone who knows very little about these topics. I should perhaps in this context point out to people new to this blog that even though I hardly consider myself an expert on these sorts of topics, I have nevertheless read quite a bit of stuff about those things in the past – books like this, this, this, this, this, this, this, this, this, this, this, this, this, this, and this one – so I was reading the book perhaps mainly from the vantage point of someone at least somewhat familiar both with many of the basic ideas and with a lot of the refinements of these ideas that people have added to the science of biology since Darwin’s time. One of the things my knowledge of modern biology and related topics had not prepared me for was how moronic some of the ideas of Darwin’s critics were at the time and how stupid some of the implicit alternatives were, and this is actually part of the fun of reading this book; there was a lot of stuff back then which even many of the people presumably held in high regard really had no clue about, and even outrageously idiotic ideas were seemingly taken quite seriously by people involved in the debate. I assume that biologists still to this day have to spend quite a bit of time and effort dealing with ignorant idiots (see also this), but back in Darwin’s day these people were presumably to a much greater extent taken seriously even among people in the scientific community, if indeed they were not themselves part of the scientific community.

Darwin was not right about everything and there’s a lot of stuff that modern biologists know which he had no idea about, so naturally some mistaken ideas made their way into Origin as well; for example the idea of the inheritance of acquired characteristics (Lamarckian inheritance) occasionally pops up and is implicitly defended in the book as a credible complement to natural selection, as also noted in Oliver Francis’ afterword to the book. On a general note it seems that Darwin did a better job convincing people about the importance of the concept of evolution than he did convincing people that the relevant mechanism behind evolution was natural selection; at least that’s what’s argued in wiki’s featured article on the history of evolutionary thought (to which I have linked before here on the blog).

Darwin emphasizes more than once in the book that evolution is a very slow process which takes a lot of time (for example: “I do believe that natural selection will always act very slowly, often only at long intervals of time, and generally on only a very few of the inhabitants of the same region at the same time”, p.123), and arguably this is also something about which he is part right/part wrong because the speed with which natural selection ‘makes itself felt’ depends upon a variety of factors, and it can be really quite fast in some contexts (see e.g. this and some of the topics covered in books like this one); though you can appreciate why he held the views he did on that topic.

A big problem confronted by Darwin was that he didn’t know how genes work, so in a sense the whole topic of the ‘mechanics of the whole thing’ – the ‘nuts and bolts’ – was more or less a black box to him (I have included a few quotes which indirectly relate to this problem in my coverage of the book below; as can be inferred from those quotes Darwin wasn’t completely clueless, but he might have benefited greatly from a chat with Gregor Mendel…) – in a way a really interesting thing about the book is how plausible the theory of natural selection is made out to be despite this blatantly obvious (at least to the modern reader) problem. Darwin was incidentally well aware there was a problem; just 6 pages into the first chapter of the book he observes frankly that: “The laws governing inheritance are quite unknown”. Some of the quotes below, e.g. on reciprocal crosses, illustrate that he was sort of scratching the surface, but in the book he never does more than that.

Below I have added some quotes from the book.

“Certainly no clear line of demarcation has as yet been drawn between species and sub-species […]; or, again, between sub-species and well-marked varieties, or between lesser varieties and individual differences. These differences blend into each other in an insensible series; and a series impresses the mind with the idea of an actual passage. […] I look at individual differences, though of small interest to the systematist, as of high importance […], as being the first step towards such slight varieties as are barely thought worth recording in works on natural history. And I look at varieties which are in any degree more distinct and permanent, as steps leading to more strongly marked and more permanent varieties; and at these latter, as leading to sub-species, and to species. […] I attribute the passage of a variety, from a state in which it differs very slightly from its parent to one in which it differs more, to the action of natural selection in accumulating […] differences of structure in certain definite directions. Hence I believe a well-marked variety may be justly called an incipient species […] I look at the term species as one arbitrarily given, for the sake of convenience, to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, and for mere convenience’ sake. […] the species of large genera present a strong analogy with varieties. And we can clearly understand these analogies, if species have once existed as varieties, and have thus originated: whereas, these analogies are utterly inexplicable if each species has been independently created.”

“Owing to [the] struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man’s power of selection. We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of Nature. But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man’s feeble efforts, as the works of Nature are to those of Art. […] In looking at Nature, it is most necessary to keep the foregoing considerations always in mind – never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount. The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force. […] A corollary of the highest importance may be deduced from the foregoing remarks, namely, that the structure of every organic being is related, in the most essential yet often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has to escape, or on which it preys.”

“Under nature, the slightest difference of structure or constitution may well turn the nicely-balanced scale in the struggle for life, and so be preserved. How fleeting are the wishes and efforts of man! how short his time! And consequently how poor will his products be, compared with those accumulated by nature during whole geological periods. […] It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapses of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were.”

“I have collected so large a body of facts, showing, in accordance with the almost universal belief of breeders, that with animals and plants a cross between different varieties, or between individuals of the same variety but of another strain, gives vigour and fertility to the offspring; and on the other hand, that close interbreeding diminishes vigour and fertility; that these facts alone incline me to believe that it is a general law of nature (utterly ignorant though we be of the meaning of the law) that no organic being self-fertilises itself for an eternity of generations; but that a cross with another individual is occasionally perhaps at very long intervals — indispensable. […] in many organic beings, a cross between two individuals is an obvious necessity for each birth; in many others it occurs perhaps only at long intervals; but in none, as I suspect, can self-fertilisation go on for perpetuity.”

“as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct. The forms which stand in closest competition with those undergoing modification and improvement, will naturally suffer most. […] Whatever the cause may be of each slight difference in the offspring from their parents – and a cause for each must exist – it is the steady accumulation, through natural selection, of such differences, when beneficial to the individual, which gives rise to all the more important modifications of structure, by which the innumerable beings on the face of this earth are enabled to struggle with each other, and the best adapted to survive.”

“Natural selection, as has just been remarked, leads to divergence of character and to much extinction of the less improved and intermediate forms of life. On these principles, I believe, the nature of the affinities of all organic beings may be explained. It is a truly wonderful fact – the wonder of which we are apt to overlook from familiarity – that all animals and all plants throughout all time and space should be related to each other in group subordinate to group, in the manner which we everywhere behold – namely, varieties of the same species most closely related together, species of the same genus less closely and unequally related together, forming sections and sub-genera, species of distinct genera much less closely related, and genera related in different degrees, forming sub-families, families, orders, sub-classes, and classes. The several subordinate groups in any class cannot be ranked in a single file, but seem rather to be clustered round points, and these round other points, and so on in almost endless cycles. On the view that each species has been independently created, I can see no explanation of this great fact in the classification of all organic beings; but, to the best of my judgment, it is explained through inheritance and the complex action of natural selection, entailing extinction and divergence of character […] The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.”

“No one has been able to point out what kind, or what amount, of difference in any recognisable character is sufficient to prevent two species crossing. It can be shown that plants most widely different in habit and general appearance, and having strongly marked differences in every part of the flower, even in the pollen, in the fruit, and in the cotyledons, can be crossed. […] By a reciprocal cross between two species, I mean the case, for instance, of a stallion-horse being first crossed with a female-ass, and then a male-ass with a mare: these two species may then be said to have been reciprocally crossed. There is often the widest possible difference in the facility of making reciprocal crosses. Such cases are highly important, for they prove that the capacity in any two species to cross is often completely independent of their systematic affinity, or of any recognisable difference in their whole organisation. On the other hand, these cases clearly show that the capacity for crossing is connected with constitutional differences imperceptible by us, and confined to the reproductive system. […] fertility in the hybrid is independent of its external resemblance to either pure parent. […] The foregoing rules and facts […] appear to me clearly to indicate that the sterility both of first crosses and of hybrids is simply incidental or dependent on unknown differences, chiefly in the reproductive systems, of the species which are crossed. […] Laying aside the question of fertility and sterility, in all other respects there seems to be a general and close similarity in the offspring of crossed species, and of crossed varieties. If we look at species as having been specially created, and at varieties as having been produced by secondary laws, this similarity would be an astonishing fact. But it harmonizes perfectly with the view that there is no essential distinction between species and varieties. […] the facts briefly given in this chapter do not seem to me opposed to, but even rather to support the view, that there is no fundamental distinction between species and varieties.”

“Believing, from reasons before alluded to, that our continents have long remained in nearly the same relative position, though subjected to large, but partial oscillations of level, I am strongly inclined to…” (…’probably get some things wrong…’, US)

“In considering the distribution of organic beings over the face of the globe, the first great fact which strikes us is, that neither the similarity nor the dissimilarity of the inhabitants of various regions can be accounted for by their climatal and other physical conditions. Of late, almost every author who has studied the subject has come to this conclusion. […] A second great fact which strikes us in our general review is, that barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions of various regions. […] A third great fact, partly included in the foregoing statements, is the affinity of the productions of the same continent or sea, though the species themselves are distinct at different points and stations. It is a law of the widest generality, and every continent offers innumerable instances. Nevertheless the naturalist in travelling, for instance, from north to south never fails to be struck by the manner in which successive groups of beings, specifically distinct, yet clearly related, replace each other. […] We see in these facts some deep organic bond, prevailing throughout space and time, over the same areas of land and water, and independent of their physical conditions. The naturalist must feel little curiosity, who is not led to inquire what this bond is.  This bond, on my theory, is simply inheritance […] The dissimilarity of the inhabitants of different regions may be attributed to modification through natural selection, and in a quite subordinate degree to the direct influence of different physical conditions. The degree of dissimilarity will depend on the migration of the more dominant forms of life from one region into another having been effected with more or less ease, at periods more or less remote; on the nature and number of the former immigrants; and on their action and reaction, in their mutual struggles for life; the relation of organism to organism being, as I have already often remarked, the most important of all relations. Thus the high importance of barriers comes into play by checking migration; as does time for the slow process of modification through natural selection. […] On this principle of inheritance with modification, we can understand how it is that sections of genera, whole genera, and even families are confined to the same areas, as is so commonly and notoriously the case.”

“the natural system is founded on descent with modification […] and […] all true classification is genealogical; […] community of descent is the hidden bond which naturalists have been unconsciously seeking, […] not some unknown plan or creation, or the enunciation of general propositions, and the mere putting together and separating objects more or less alike.”

September 27, 2015 Posted by | Biology, Books, Botany, Evolutionary biology, Genetics, Geology, Zoology | Leave a comment

Wikipedia articles of interest

i. Motte-and-bailey castle (‘good article’).

“A motte-and-bailey castle is a fortification with a wooden or stone keep situated on a raised earthwork called a motte, accompanied by an enclosed courtyard, or bailey, surrounded by a protective ditch and palisade. Relatively easy to build with unskilled, often forced labour, but still militarily formidable, these castles were built across northern Europe from the 10th century onwards, spreading from Normandy and Anjou in France, into the Holy Roman Empire in the 11th century. The Normans introduced the design into England and Wales following their invasion in 1066. Motte-and-bailey castles were adopted in Scotland, Ireland, the Low Countries and Denmark in the 12th and 13th centuries. By the end of the 13th century, the design was largely superseded by alternative forms of fortification, but the earthworks remain a prominent feature in many countries. […]

Various methods were used to build mottes. Where a natural hill could be used, scarping could produce a motte without the need to create an artificial mound, but more commonly much of the motte would have to be constructed by hand.[19] Four methods existed for building a mound and a tower: the mound could either be built first, and a tower placed on top of it; the tower could alternatively be built on the original ground surface and then buried within the mound; the tower could potentially be built on the original ground surface and then partially buried within the mound, the buried part forming a cellar beneath; or the tower could be built first, and the mound added later.[25]

Regardless of the sequencing, artificial mottes had to be built by piling up earth; this work was undertaken by hand, using wooden shovels and hand-barrows, possibly with picks as well in the later periods.[26] Larger mottes took disproportionately more effort to build than their smaller equivalents, because of the volumes of earth involved.[26] The largest mottes in England, such as Thetford, are estimated to have required up to 24,000 man-days of work; smaller ones required perhaps as little as 1,000.[27] […] Taking into account estimates of the likely available manpower during the period, historians estimate that the larger mottes might have taken between four and nine months to build.[29] This contrasted favourably with stone keeps of the period, which typically took up to ten years to build.[30] Very little skilled labour was required to build motte and bailey castles, which made them very attractive propositions if forced peasant labour was available, as was the case after the Norman invasion of England.[19] […]

The type of soil would make a difference to the design of the motte, as clay soils could support a steeper motte, whilst sandier soils meant that a motte would need a more gentle incline.[14] Where available, layers of different sorts of earth, such as clay, gravel and chalk, would be used alternatively to build in strength to the design.[32] Layers of turf could also be added to stabilise the motte as it was built up, or a core of stones placed as the heart of the structure to provide strength.[33] Similar issues applied to the defensive ditches, where designers found that the wider the ditch was dug, the deeper and steeper the sides of the scarp could be, making it more defensive. […]

Although motte-and-bailey castles are the best known castle design, they were not always the most numerous in any given area.[36] A popular alternative was the ringwork castle, involving a palisade being built on top of a raised earth rampart, protected by a ditch. The choice of motte and bailey or ringwork was partially driven by terrain, as mottes were typically built on low ground, and on deeper clay and alluvial soils.[37] Another factor may have been speed, as ringworks were faster to build than mottes.[38] Some ringwork castles were later converted into motte-and-bailey designs, by filling in the centre of the ringwork to produce a flat-topped motte. […]

In England, William invaded from Normandy in 1066, resulting in three phases of castle building in England, around 80% of which were in the motte-and-bailey pattern. […] around 741 motte-and-bailey castles [were built] in England and Wales alone. […] Many motte-and-bailey castles were occupied relatively briefly and in England many were being abandoned by the 12th century, and others neglected and allowed to lapse into disrepair.[96] In the Low Countries and Germany, a similar transition occurred in the 13th and 14th centuries. […] One factor was the introduction of stone into castle building. The earliest stone castles had emerged in the 10th century […] Although wood was a more powerful defensive material than was once thought, stone became increasingly popular for military and symbolic reasons.”

ii. Battle of Midway (featured). Lots of good stuff in there. One aspect I had not been aware of beforehand was that Allied codebreakers also here (I was quite familiar with the works of Turing and others in Bletchley Park) played a key role:

“Admiral Nimitz had one priceless advantage: cryptanalysts had partially broken the Japanese Navy’s JN-25b code.[45] Since the early spring of 1942, the US had been decoding messages stating that there would soon be an operation at objective “AF”. It was not known where “AF” was, but Commander Joseph J. Rochefort and his team at Station HYPO were able to confirm that it was Midway; Captain Wilfred Holmes devised a ruse of telling the base at Midway (by secure undersea cable) to broadcast an uncoded radio message stating that Midway’s water purification system had broken down.[46] Within 24 hours, the code breakers picked up a Japanese message that “AF was short on water.”[47] HYPO was also able to determine the date of the attack as either 4 or 5 June, and to provide Nimitz with a complete IJN order of battle.[48] Japan had a new codebook, but its introduction had been delayed, enabling HYPO to read messages for several crucial days; the new code, which had not yet been cracked, came into use shortly before the attack began, but the important breaks had already been made.[49][nb 8]

As a result, the Americans entered the battle with a very good picture of where, when, and in what strength the Japanese would appear. Nimitz knew that the Japanese had negated their numerical advantage by dividing their ships into four separate task groups, all too widely separated to be able to support each other.[50][nb 9] […] The Japanese, by contrast, remained almost totally unaware of their opponent’s true strength and dispositions even after the battle began.[27] […] Four Japanese aircraft carriers — Akagi, Kaga, Soryu and Hiryu, all part of the six-carrier force that had attacked Pearl Harbor six months earlier — and a heavy cruiser were sunk at a cost of the carrier Yorktown and a destroyer. After Midway and the exhausting attrition of the Solomon Islands campaign, Japan’s capacity to replace its losses in materiel (particularly aircraft carriers) and men (especially well-trained pilots) rapidly became insufficient to cope with mounting casualties, while the United States’ massive industrial capabilities made American losses far easier to bear. […] The Battle of Midway has often been called “the turning point of the Pacific”.[140] However, the Japanese continued to try to secure more strategic territory in the South Pacific, and the U.S. did not move from a state of naval parity to one of increasing supremacy until after several more months of hard combat.[141] Thus, although Midway was the Allies’ first major victory against the Japanese, it did not radically change the course of the war. Rather, it was the cumulative effects of the battles of Coral Sea and Midway that reduced Japan’s ability to undertake major offensives.[9]

One thing which really strikes you (well, struck me) when reading this stuff is how incredibly capital-intensive the war at sea really was; this was one of the most important sea battles of the Second World War, yet the total Japanese death toll at Midway was just 3,057. To put that number into perspective, it is significantly smaller than the average number of people killed each day in Stalingrad (according to one estimate, the Soviets alone suffered 478,741 killed or missing during those roughly 5 months (~150 days), which comes out at roughly 3000/day).

iii. History of time-keeping devices (featured). ‘Exactly what it says on the tin’, as they’d say on TV Tropes.

Clepsydra-Diagram-Fancy
It took a long time to get from where we were to where we are today; the horologists of the past faced a lot of problems you’ve most likely never even thought about. What do you do for example do if your ingenious water clock has trouble keeping time because variation in water temperature causes issues? Well, you use mercury instead of water, of course! (“Since Yi Xing’s clock was a water clock, it was affected by temperature variations. That problem was solved in 976 by Zhang Sixun by replacing the water with mercury, which remains liquid down to −39 °C (−38 °F).”).

iv. Microbial metabolism.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe’s ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles. […]

All microbial metabolisms can be arranged according to three principles:

1. How the organism obtains carbon for synthesising cell mass:

2. How the organism obtains reducing equivalents used either in energy conservation or in biosynthetic reactions:

3. How the organism obtains energy for living and growing:

In practice, these terms are almost freely combined. […] Most microbes are heterotrophic (more precisely chemoorganoheterotrophic), using organic compounds as both carbon and energy sources. […] Heterotrophic microbes are extremely abundant in nature and are responsible for the breakdown of large organic polymers such as cellulose, chitin or lignin which are generally indigestible to larger animals. Generally, the breakdown of large polymers to carbon dioxide (mineralization) requires several different organisms, with one breaking down the polymer into its constituent monomers, one able to use the monomers and excreting simpler waste compounds as by-products, and one able to use the excreted wastes. There are many variations on this theme, as different organisms are able to degrade different polymers and secrete different waste products. […]

Biochemically, prokaryotic heterotrophic metabolism is much more versatile than that of eukaryotic organisms, although many prokaryotes share the most basic metabolic models with eukaryotes, e. g. using glycolysis (also called EMP pathway) for sugar metabolism and the citric acid cycle to degrade acetate, producing energy in the form of ATP and reducing power in the form of NADH or quinols. These basic pathways are well conserved because they are also involved in biosynthesis of many conserved building blocks needed for cell growth (sometimes in reverse direction). However, many bacteria and archaea utilize alternative metabolic pathways other than glycolysis and the citric acid cycle. […] The metabolic diversity and ability of prokaryotes to use a large variety of organic compounds arises from the much deeper evolutionary history and diversity of prokaryotes, as compared to eukaryotes. […]

Many microbes (phototrophs) are capable of using light as a source of energy to produce ATP and organic compounds such as carbohydrates, lipids, and proteins. Of these, algae are particularly significant because they are oxygenic, using water as an electron donor for electron transfer during photosynthesis.[11] Phototrophic bacteria are found in the phyla Cyanobacteria, Chlorobi, Proteobacteria, Chloroflexi, and Firmicutes.[12] Along with plants these microbes are responsible for all biological generation of oxygen gas on Earth. […] As befits the large diversity of photosynthetic bacteria, there are many different mechanisms by which light is converted into energy for metabolism. All photosynthetic organisms locate their photosynthetic reaction centers within a membrane, which may be invaginations of the cytoplasmic membrane (Proteobacteria), thylakoid membranes (Cyanobacteria), specialized antenna structures called chlorosomes (Green sulfur and non-sulfur bacteria), or the cytoplasmic membrane itself (heliobacteria). Different photosynthetic bacteria also contain different photosynthetic pigments, such as chlorophylls and carotenoids, allowing them to take advantage of different portions of the electromagnetic spectrum and thereby inhabit different niches. Some groups of organisms contain more specialized light-harvesting structures (e.g. phycobilisomes in Cyanobacteria and chlorosomes in Green sulfur and non-sulfur bacteria), allowing for increased efficiency in light utilization. […]

Most photosynthetic microbes are autotrophic, fixing carbon dioxide via the Calvin cycle. Some photosynthetic bacteria (e.g. Chloroflexus) are photoheterotrophs, meaning that they use organic carbon compounds as a carbon source for growth. Some photosynthetic organisms also fix nitrogen […] Nitrogen is an element required for growth by all biological systems. While extremely common (80% by volume) in the atmosphere, dinitrogen gas (N2) is generally biologically inaccessible due to its high activation energy. Throughout all of nature, only specialized bacteria and Archaea are capable of nitrogen fixation, converting dinitrogen gas into ammonia (NH3), which is easily assimilated by all organisms.[14] These prokaryotes, therefore, are very important ecologically and are often essential for the survival of entire ecosystems. This is especially true in the ocean, where nitrogen-fixing cyanobacteria are often the only sources of fixed nitrogen, and in soils, where specialized symbioses exist between legumes and their nitrogen-fixing partners to provide the nitrogen needed by these plants for growth.

Nitrogen fixation can be found distributed throughout nearly all bacterial lineages and physiological classes but is not a universal property. Because the enzyme nitrogenase, responsible for nitrogen fixation, is very sensitive to oxygen which will inhibit it irreversibly, all nitrogen-fixing organisms must possess some mechanism to keep the concentration of oxygen low. […] The production and activity of nitrogenases is very highly regulated, both because nitrogen fixation is an extremely energetically expensive process (16–24 ATP are used per N2 fixed) and due to the extreme sensitivity of the nitrogenase to oxygen.” (A lot of the stuff above was of course for me either review or closely related to stuff I’ve already read in the coverage provided in Beer et al., a book I’ve talked about before here on the blog).

v. Uranium (featured). It’s hard to know what to include here as the article has a lot of stuff, but I found this part in particular, well, interesting:

“During the Cold War between the Soviet Union and the United States, huge stockpiles of uranium were amassed and tens of thousands of nuclear weapons were created using enriched uranium and plutonium made from uranium. Since the break-up of the Soviet Union in 1991, an estimated 600 short tons (540 metric tons) of highly enriched weapons grade uranium (enough to make 40,000 nuclear warheads) have been stored in often inadequately guarded facilities in the Russian Federation and several other former Soviet states.[12] Police in Asia, Europe, and South America on at least 16 occasions from 1993 to 2005 have intercepted shipments of smuggled bomb-grade uranium or plutonium, most of which was from ex-Soviet sources.[12] From 1993 to 2005 the Material Protection, Control, and Accounting Program, operated by the federal government of the United States, spent approximately US $550 million to help safeguard uranium and plutonium stockpiles in Russia.[12] This money was used for improvements and security enhancements at research and storage facilities. Scientific American reported in February 2006 that in some of the facilities security consisted of chain link fences which were in severe states of disrepair. According to an interview from the article, one facility had been storing samples of enriched (weapons grade) uranium in a broom closet before the improvement project; another had been keeping track of its stock of nuclear warheads using index cards kept in a shoe box.[45]

Some other observations from the article below:

“Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of abundance in the Earth’s crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements.[10] Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernovae.[46] The decay of uranium, thorium, and potassium-40 in the Earth’s mantle is thought to be the main source of heat[47][48] that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics. […]

Natural uranium consists of three major isotopes: uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). […] Uranium-238 is the most stable isotope of uranium, with a half-life of about 4.468×109 years, roughly the age of the Earth. Uranium-235 has a half-life of about 7.13×108 years, and uranium-234 has a half-life of about 2.48×105 years.[82] For natural uranium, about 49% of its alpha rays are emitted by each of 238U atom, and also 49% by 234U (since the latter is formed from the former) and about 2.0% of them by the 235U. When the Earth was young, probably about one-fifth of its uranium was uranium-235, but the percentage of 234U was probably much lower than this. […]

Worldwide production of U3O8 (yellowcake) in 2013 amounted to 70,015 tonnes, of which 22,451 t (32%) was mined in Kazakhstan. Other important uranium mining countries are Canada (9,331 t), Australia (6,350 t), Niger (4,518 t), Namibia (4,323 t) and Russia (3,135 t).[55] […] Australia has 31% of the world’s known uranium ore reserves[61] and the world’s largest single uranium deposit, located at the Olympic Dam Mine in South Australia.[62] There is a significant reserve of uranium in Bakouma a sub-prefecture in the prefecture of Mbomou in Central African Republic. […] Uranium deposits seem to be log-normal distributed. There is a 300-fold increase in the amount of uranium recoverable for each tenfold decrease in ore grade.[75] In other words, there is little high grade ore and proportionately much more low grade ore available.”

vi. Radiocarbon dating (featured).

Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method of determining the age of an object containing organic material by using the properties of radiocarbon (14C), a radioactive isotope of carbon. The method was invented by Willard Libby in the late 1940s and soon became a standard tool for archaeologists. Libby received the Nobel Prize for his work in 1960. The radiocarbon dating method is based on the fact that radiocarbon is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14C it contains begins to reduce as the 14C undergoes radioactive decay. Measuring the amount of 14C in a sample from a dead plant or animal such as piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14C there is to be detected, and because the half-life of 14C (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by radiocarbon dating are around 50,000 years ago, although special preparation methods occasionally permit dating of older samples.

The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained. […]

The development of radiocarbon dating has had a profound impact on archaeology. In addition to permitting more accurate dating within archaeological sites than did previous methods, it allows comparison of dates of events across great distances. Histories of archaeology often refer to its impact as the “radiocarbon revolution”.”

I’ve read about these topics before in a textbook setting (e.g. here), but/and I should note that the article provides quite detailed coverage and I think most people will encounter some new information by having a look at it even if they’re superficially familiar with this topic. The article has a lot of stuff about e.g. ‘what you need to correct for’, which some of you might find interesting.

vii. Raccoon (featured). One interesting observation from the article:

“One aspect of raccoon behavior is so well known that it gives the animal part of its scientific name, Procyon lotor; “lotor” is neo-Latin for “washer”. In the wild, raccoons often dabble for underwater food near the shore-line. They then often pick up the food item with their front paws to examine it and rub the item, sometimes to remove unwanted parts. This gives the appearance of the raccoon “washing” the food. The tactile sensitivity of raccoons’ paws is increased if this rubbing action is performed underwater, since the water softens the hard layer covering the paws.[126] However, the behavior observed in captive raccoons in which they carry their food to water to “wash” or douse it before eating has not been observed in the wild.[127] Naturalist Georges-Louis Leclerc, Comte de Buffon, believed that raccoons do not have adequate saliva production to moisten food thereby necessitating dousing, but this hypothesis is now considered to be incorrect.[128] Captive raccoons douse their food more frequently when a watering hole with a layout similar to a stream is not farther away than 3 m (10 ft).[129] The widely accepted theory is that dousing in captive raccoons is a fixed action pattern from the dabbling behavior performed when foraging at shores for aquatic foods.[130] This is supported by the observation that aquatic foods are doused more frequently. Cleaning dirty food does not seem to be a reason for “washing”.[129] Experts have cast doubt on the veracity of observations of wild raccoons dousing food.[131]

And here’s another interesting set of observations:

“In Germany—where the racoon is called the Waschbär (literally, “wash-bear” or “washing bear”) due to its habit of “dousing” food in water—two pairs of pet raccoons were released into the German countryside at the Edersee reservoir in the north of Hesse in April 1934 by a forester upon request of their owner, a poultry farmer.[186] He released them two weeks before receiving permission from the Prussian hunting office to “enrich the fauna.” [187] Several prior attempts to introduce raccoons in Germany were not successful.[188] A second population was established in eastern Germany in 1945 when 25 raccoons escaped from a fur farm at Wolfshagen, east of Berlin, after an air strike. The two populations are parasitologically distinguishable: 70% of the raccoons of the Hessian population are infected with the roundworm Baylisascaris procyonis, but none of the Brandenburgian population has the parasite.[189] The estimated number of raccoons was 285 animals in the Hessian region in 1956, over 20,000 animals in the Hessian region in 1970 and between 200,000 and 400,000 animals in the whole of Germany in 2008.[158][190] By 2012 it was estimated that Germany now had more than a million raccoons.[191]

June 14, 2015 Posted by | Archaeology, Biology, Botany, Geology, History, Microbiology, Physics, Wikipedia, Zoology | Leave a comment

Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe (3)

Here’s a previous post in the series. In this post I’ll pick up roughly where I left off in my last post, around the time of the ‘Grande Coupure‘ roughly 34 million years ago.

“The extinction of the arboreal primates and the reduction or extinction of several browsing groups […] are strong evidence for the retreat of the forests during the early Oligocene and their replacement by open woodlands or even drier biotopes. […] Among the most distinctive species to enter Europe after the “Grande Coupure” were the first true rhinoceroses [which] achieved a high diversity and were going to characterize the mammalian faunas of Europe for millions of years, until the extinction of the last woolly rhinos during the late Pleistocene. […] the evolution of this group produced the largest terrestrial mammals of any time. The giant Paraceratherium […] was 6 m tall at the shoulders and had a 1.5-m-long skull […]. The males of this animal weighed around 15 tons, while the females were somewhat smaller, about 10 tons.” [Wikipedia has a featured article about these things here].

“One of the most significant features of the early Oligocene small-mammal communities was the first entry of lagomorphs into Europe. The lagomorphs — that is, the order of mammals that includes today’s hares and rabbits — originated very early on the Asian continent and from there colonized North America. The presence of the Turgai Strait prevented this group from entering Europe during the Eocene. […] the most characteristic immigrants during the early Oligocene were the cricetids of the genus Atavocricetodon. The cricetids are today represented in Europe by hamsters, reduced to three or four species […] These cricetids are typical inhabitants of the cold steppes of eastern Europe and Central Asia, and their limited representation in today’s European ecosystems does not reflect their importance in the history of the Cenozoic mammalian faunas of Eurasia. After its first entry following the “Grande Coupure,” this group experienced extraordinary success, diversifying into several genera and species. Even more significantly, the cricetids gave rise to the rodent groups that were going to be dominant during the Pliocene and Pleistocene — that is, the murids (the family of mice and rats) and arvicolids (the family of voles). […] In addition, new carnivore families, like the nimravids, appeared […]. The nimravids were once regarded as true felids (the family that includes today’s big and small cats) because of their similar dental and cranial adaptations. […] one of the more distinctive attributes of the nimravids was their long, laterally flattened upper canines, which were similar to those of the Miocene and Pliocene saber-toothed cats […]. However, most of these features have proved to be the result of a similar adaptation to hypercarnivorism, and the nimravids are now placed in a separate family of early carnivores whose evolution paralleled that of the large saber-toothed felids.” [Actually some of the nimravids were in some sense ‘even more sabertoothed’ than the (‘true’) saber-toothed cats which came later: “Although [the nimravid] Eusmilus bidentatus was no larger than a modern lynx, the adaptations for gape seen on its skull and mandible are more advanced than in any of the felid sabertooths of the European Pliocene and Pleistocene.”]

“About 30 million years ago, a new glacial phase began, and for 4 million years Antarctica was subjected to multiple glaciation episodes. The global sea level experienced the largest lowering in the whole Cenozoic, dropping by about 150 m […]. A possible explanation for this new glacial event lies in the final opening of the Drake Passage between Antarctica and South America, which led to the completion of a fully circumpolar circulation and impeded any heat exchange between Antarctic waters and the warmer equatorial waters. A second, perhaps complementary cause for this glacial pulse is probably related to the final opening of the seaway between Greenland and Norway. The cold Arctic waters, largely isolated since the Mesozoic, spread at this time into the North Atlantic. The main effect of this cooling was a new extension of the dry landscapes on the European and western Asian lands. For instance, we know from pollen evidence that a desert vegetation was dominant in the Levant during the late Oligocene and earliest Miocene […] This glacial event led to the extinction of several forms that had persisted from the Eocene”.

“Among the carnivores, the late Oligocene saw the decline and local extinction of the large nimravids [Key word: local. They came back to Europe later during the early Miocene, and “the nimravids maintained a remarkable stability throughout the Miocene, probably in relation to a low speciation rate”]. In contrast, the group of archaic feloids that had arisen during the early Oligocene […] continued its evolution into the late Oligocene and diversified into a number of genera […] The other group of large carnivores that spread during the late Oligocene were the “bear-dog” amphicyonids, which from that time on became quite diverse, with many different ecological adaptations. […] The late Oligocene saw, in addition to the bearlike amphicyonids, the spread of the first true ursids […]. The members of this genus did not have the massive body dimensions of today’s bears but were medium-size omnivores […] Another group of carnivores that spread successfully during the late Oligocene were the mustelids, the family that includes today’s martens, badgers, skunks, and otters. […] In contrast to these successes, the creodonts of the genus Hyaenodon, which had survived all periods of crisis since the Eocene, declined during the late Oligocene. The last Hyaenodon in Europe was recorded at the end of the Oligocene […], and did not survive into the Miocene. This was the end in Europe of a long-lived group of successful carnivorans that had filled the large-predator guild for millions of years. However, as with other Oligocene groups, […] the hyaenodonts persisted in Africa and, from there, made a short incursion into Europe during the early Miocene”.

“After a gradual warming during the late Oligocene, global temperatures reached a climatic optimum during the early Miocene […] Shallow seas covered several nearshore areas in Europe […] as a consequence of a general sea-level rise. A broad connection was established between the Indian Ocean and both the Mediterranean and Paratethys Seas […] Widespread warm-water faunas including tropical fishes and nautiloids have been found, indicating conditions similar to those of the present-day Guinea Gulf, with mean surface-water temperatures around 25 to 27°C. Important reef formations bounded most of the shallow-water Mediterranean basins. […] Reef-building corals that today inhabit the Great Barrier Reef within a temperature range of 19 to 28°C became well established on North Island, New Zealand […] The early Miocene climate was warm and humid, indicating tropical conditions […]. Rich, extensive woodlands with varied kinds of plants developed in different parts of southern Europe […] The climatic optimum of the early Miocene also led to a maximum development of mangroves. These subtropical floras extended as far north as eastern Siberia and Kamchatka”.

“Despite the climatic stability of the early Miocene, an important tectonic event disrupted the evolution of the Eurasian faunas during this epoch. About 19 million years ago, the graben system along the Red Sea Fault, active in the south since the late Oligocene, opened further […] Consequently, the Arabian plate rotated counterclockwise and collided with the Anatolian plate. The marine gateway from the Mediterranean toward the Indo-Pacific closed, and a continental migration bridge (known as the Gomphothere Bridge) between Eurasia and Africa came into existence. This event had enormous consequences for the further evolution of the terrestrial faunas of Eurasia and Africa. Since the late Eocene, Africa had evolved in isolation, developing its own autochthonous fauna. Part of this fauna consisted of a number of endemic Oligocene survivors, such as anthracotheres, hyaenodonts, and primates, for which Africa had acted as a refuge […] The first evidence of an African–Eurasian exchange was the presence of the anthracothere Brachyodus in a number of early Miocene sites in Europe […] a second dispersal event from Africa, that of the gomphothere and deinothere proboscideans, had much more lasting effects. […] Today we can easily identify any proboscidean by its long proboscis and tusks. However, the primitive proboscideans from the African Eocene had a completely different appearance and are hardly recognizable as the ancestors of today’s elephants. Instead, they were hippolike semiamphibious ungulates with massive, elongated bodies supported by rather short legs. […] The first proboscideans entering Europe were the so-called gomphotheres […] which dispersed worldwide during the early Miocene from Africa to Europe, Asia, and North America […]. Gomphotherium was the size of an Indian elephant, about 2.5 m high at the withers. Its skull and dentition, however, were different from those of modern elephants. Gomphotherium’s skull was long […] and displayed not two but four tusks, one pair in the upper jaw and the other pair at the end of the lower jaw. […] Shortly after the entry of Gomphotherium and Zygolophodon [a second group of mastodons], a third proboscidean group, the deinotheres, successfully settled in Eurasia. Unlike the previous genera, the deinotheres were not elephantoids but represented a different, now totally extinct kind of proboscidean.”

“The dispersal of not only the African proboscideans but also many eastern immigrants contributed to a significant increase in the diversity of the impoverished early Miocene terrestrial biotas. The entry of this set of immigrants probably led to the extinction of a number of late Oligocene and early Miocene survivors, such as tapirids, anthracotherids, and primitive suids [pigs] and moschoids. In addition to the events that affected the Middle East area, sea-level fluctuations enabled short-lived mammal exchanges across the Bering Strait between Eurasia and North America, permitting the arrival of the browsing horse Anchitherium in Eurasia […] Widely used for biostragraphic purposes, the dispersal of Anchitherium was the first of a number of similar isolated events undergone by North American equids that entered Eurasia and rapidly spread on this continental area.”

“A new marine transgression, known as the Langhian Transgression, characterized the beginning of the middle Miocene, affecting the circum-Mediterranean area. Consequently, the seaway to the Indo-Pacific reopened for a short time, restoring the circum-equatorial warm-water circulation. […] tropical conditions became established as far north as Poland in marine coastal and open-sea waters. After the optimal conditions of the early Miocene, the middle Miocene was a period of global oceanic reorganization, representing a major change in the climatic evolution of the Cenozoic. Before this process began, high-latitude paleoclimatic conditions were generally warm although oscillating, but they rapidly cooled thereafter, leading to an abrupt high-latitude cooling event at about 14.5 million years ago […] Increased production of cold, deep Antarctic waters caused the extinction of several oceanic benthic foraminifers that had persisted from the late Oligocene–early Miocene and promoted a significant evolutionary turnover of the oceanic assemblages from about 16 to 14 million years ago […] This middle Miocene cooling was associated with a major growth of the Eastern Antarctic Ice Sheets (EAIS) […] Middle Miocene polar cooling and east Antarctic ice growth had severe effects on middle- to low-latitude terrestrial environments. There was a climatic trend to cooler winters and decreased summer rainfall. Seasonal, summer-drought-adapted schlerophyllous vegetation progressively evolved and spread geographically during the Miocene, replacing the laurophyllous evergreen forests that were adapted to moist, subtropical and tropical conditions with temperate winters and abundant summer rainfalls […] These effects were clearly seen in a wide area to the south of the Paratethys Sea, extending from eastern Europe to western Asia. According to the ideas of the American paleontologist Ray Bernor, this region, known as the Greek-Iranian (or sub-Paratethyan) Province, acted as a woodland environmental “hub” for a corridor of open habitats that extended from northwestern Africa eastward across Arabia into Afghanistan, north into the eastern Mediterranean area, and northeast into northern China. The Greek-Iranian Province records the first evidence of open woodlands in which a number of large, progressive open-country mammals—such as hyaenids, thick-enameled hominoids, bovids, and giraffids — diversified and dispersed into eastern Africa and southwestern Asia […] the peculiar biotope developed in the Greek-Iranian Province acted as the background from which the African savannas evolved during the Pliocene and Pleistocene.”

“The most outstanding effect of the Middle Miocene Event is seen among the herbivorous community, which showed a trend toward developing larger body sizes, more-hypsodont teeth, and more-elongated distal limb segments […]. Increasing body size in herbivores is related to a higher ingestion of fibrous and low-quality vegetation. Browsers and grazers have to be large because they need long stomachs and intestines to process a large quantity of low-energy food (this is why they have to eat almost continuously). Because of the mechanism of rumination, ruminants are the only herbivores that can escape this rule and subsist at small sizes. Increasing hypsodonty and high-crowned teeth are directly related to the ingestion of more-abrasive vegetation […] Finally, the elongation of the distal limb segments is related to increasing cursoriality. The origin of cursoriality can be linked to the expansion of the home range in open, low-productive habitats. […] At the taxonomic level, this habitat change in the low latitudes involved the rapid adaptive radiation of woodland ruminants (bovids and giraffids). […] Gazelles dispersed into Europe at this time from their possible Afro-Arabian origins […] Not only gazelles but also the giraffids experienced a wide adaptive radiation into Africa after their dispersal from Asia. […] Among the suids [pigs], the listriodontines evolved in a peculiar way in northern Africa, leading to giant forms such as Kubanochoerus, with a weight of about 500 kg, which in some species may have reached 800 kg.”

March 8, 2015 Posted by | Biology, Books, climate, Evolutionary biology, Geology, Paleontology, Zoology | Leave a comment

Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe (2)

Here’s my first post about the book.

I wasn’t quite sure how to rate the book, but I ended up at four stars on goodreads. The main thing holding me back from giving it a higher rating is that the book is actually quite hard to read and there’s a lot of talk about teeth; one general point I learned from this book is that the teeth animals who lived in the past have left behind for us to find are sometimes really useful, because they can help us to make/support various inferences about other things, from animal behaviours to climatic developments. As for the ‘hard to read’-part, I (mostly) don’t blame the author for this because a book like this would have to be a bit hard to read to provide the level of coverage that is provided; that’s part of why I give it four stars in spite of this. If you have a look at the links in the first post, you’ll notice the many Latin names. You’ll find a lot of those in the text as well. This is perfectly natural as there were a lot of e.g. horse-like and rhino-like species living in the past and you need to be clear about which one of them you’re talking about now because they were all different, lived in different time periods, etc. For obvious reasons the book has a lot of talk about species/genera with no corresponding ‘familiar/popular’ names (like ‘cat’ or ‘dog’), and you need to keep track of the Latin names to make sense of the stuff; as well as keeping track of the various other Latin terms used e.g. in osteometry. So you’ll encounter some passages where there’s some talk about the differences between two groups whose names look pretty similar, and you’re told about how one group had two teeth which were a bit longer than they were in the other group and the teeth also looked slightly different (and you’ll be told exactly which teeth we’re talking about, described in a language you’d probably have to be a dentist to understand without looking up a lot of stuff along the way). Problems keeping track of the animals/groups encountered also stem from the fact that whereas some species encountered in the book do have modern counterparts, others don’t. The coverage helps you to figure out which ecological niche which group may have inhabited, but if you’re completely unfamiliar with the field of ecology I’m not sure how easy it is to get into this mindset. The text does provide some help navigating this weird landscape of the past, and the many fascinating illustrations in the book make it easier to visualize what the animals encountered along the way might have looked like, but reading the book takes some work.

That said, it’s totally worth it because this stuff’s just plain fascinating! The book isn’t quite ‘up there’ with Herrera et al. (it reminded me a bit more of van der Geer et al., not only because of the slight coverage overlap), but some of the stuff in there’s pretty damn awesome – and it’s stuff you ought to know, because it’ll probably change how you think about the world. The really neat thing about reading a book like this is that it exposes a lot of unwarranted assumptions you’ve been making without knowing it, about what the past used to be like. I’m almost certain anyone reading a book like this will encounter ideas which are very surprising to them. We look at the world through the eyes of the present, and it can be difficult to imagine just how many things used to be different. Vague and tentative ideas you might have had about how the world used to look like and how it used to work can through reading books like this one be replaced with a much more clear, and much better supported, picture of the past. Even though there’s still a lot of stuff we don’t know, and will never know. I could mention almost countless examples of things I was very surprised to learn while reading this book, and I’m sure many people reading the book would encounter even more of these, as I actually was somewhat familiar with parts of the related literature already before reading the book.

I’ve added a few sample quotes and observations from the book below.

“Europe, although just an appendage of the Eurasian supercontinent, acted during most of its history as a crossroad where Asian, African, and American faunas passed one another, throughout successive dispersal and extinction events. But these events did not happen in an isolated context, since they were the response to climatic and environmental events of a higher order. Thus this book pays special attention to the abundant literature that for the past few decades has dedicated itself to the climatic evolution of our planet.”

“A common scenario tends to posit the early evolutionary radiation of placental mammals as occurring only after the extinction of the dinosaurs at the end of the Cretaceous period. The same scenario assumes a sudden explosion of forms immediately after the End Cretaceous Mass Extinction, filling the vacancies left by the vanished reptilian faunas. But a close inspection of the first epoch of the Cenozoic provides quite a different picture: the “explosion” began well before the end of the Cretaceous period and was not sudden, but lasted millions of years throughout the first division of the Cenozoic era, the Paleocene epoch. […] our knowledge of this remote time of mammalian evolution is much more obscure and incomplete than our understanding of the other periods of the Cenozoic. […] compared with our present world, and in contrast to the succeeding epochs, the Paleocene appears to us as a strange time, in which the present orders of mammals were absent or can hardly be distinguished: no rodents, no perissodactyls, no artiodactyls, bizarre noncarnivorous carnivorans. […] although the Paleocene was mammalian in character, we do not recognize it as a clear part of our own world; it looks more like an impoverished extension of the late Cretaceous world than the seed of the present Age of Mammals.”

“The diatrymas were human-size — up to 2 m tall — ground-running birds that inhabited the terrestrial ecosystems of Europe and North America in the Paleocene and the early to middle Eocene […] Besides the large diatrymas, a large variety of crocodiles — mainly terrestrial and amphibious eusuchian crocodiles — populated the marshes of the Paleocene rainforests. […] The high diversification of the crocodile fauna throughout the Paleocene and Eocene represents a significant ecological datum, since crocodiles do not tolerate temperatures below 10 to 15°C (exceptionally, they could survive in temperatures of about 5 or 6°C). Their existence in Europe indicates that during the first part of the Cenozoic the average temperature of the coldest month never fell below these values and that these mild conditions persisted at least until the middle Miocene.”

“At the end of the Paleocene, approximately 55.5 million years ago, there was a sudden, short-term warming known as the Latest Paleocene Thermal Maximum. Over a period of tens of thousands of years or less, the temperature of all the oceans increased by around 4°C. This was the highest warming during the entire Cenozoic, reaching global mean temperatures of around 20°C. There is some evidence that the Latest Paleocene Thermal Maximum resulted from a sudden increase in atmospheric CO2. Intense volcanic activity developed at the Paleocene–Eocene boundary, associated with the rifting process in the North Atlantic and the opening of the Norwegian-Greenland Sea. […] According to some analyses, atmospheric CO2 during the early Eocene may have been eight times its present concentration. […] The high temperatures and increasing humidity favored the extension of tropical rainforests over the middle and higher latitudes, as far north as Ellesmere Island, now in the Canadian arctic north. There, an abundant fauna — including crocodiles, monitor lizards, primates, rodents, multituberculates, early perissodactyls, and the pantodont Coryphodon — and a flora composed of tropical elements indicates the extension of the forests as far north as 78 degrees north latitude. […] The global oceanic level at the beginning of the Eocene was high, and extensive areas of Eurasia were still under the sea. In this context, Europe consisted of a number of emerged islands forming a kind of archipelago. A central European island consisted of parts of present-day England, France, and Germany, although it was placed in a much more southerly position, approximately at the present latitude of Naples. […] To the east, the growing Mediterranean opened into a wide sea, since the landmasses of Turkey, Iraq, and Iran were still below sea level. To the east of the Urals, the Turgai Strait still connected the warm waters of the Tethys Sea with the Polar Sea. […] Despite the opening of the Greenland-Norwegian Sea, Europe and North America were still connected during most of the early and middle Eocene across two main land bridges […] the De Geer Corridor [and] the Thule Bridge […] these corridors must have been effective, since the European fossil record shows a massive entry of American elements […] The ischyromyid and ailuravid rodents, as well as the miacid carnivores, were among the oldest representatives of the modern orders of mammals to appear in Europe during the early Eocene. However, they were not the only ones, since the “modernization” of the mammalian communities at this time went even further, and groups such as the first true primates, bats (Chiroptera), flying lemurs (Dermoptera), and oddtoed (Perissodactyla) and even-toed (Artiodactyla) ungulates entered onto the scene, in both Europe and North America.”

“Although it was the first member of the horse lineage, Pliolophus certainly did not look like a horse. As classically stated, it had the dimensions of a medium dog (“a fox-terrier”), bearing four hooves on the front legs and three on the hind legs. […] the first rhino-related forms included Hyrachius, a small rhino about the size of a wolf that during the Eocene inhabited a wide geographic range, from North America to Europe and Asia.” (Yep, in case you didn’t know Europe had rhinos for millions and millions of years…) “The artiodactyls are among the most successful orders of mammals, having diversified in the past 10 million years into a wide array of families, subfamilies, tribes, and genera all around the world, including pigs, peccaries, hippos, chevrotains, camels, giraffes, deer, antelopes, gazelles, goats, and cattle. They are easily distinguished from the perissodactyls because each extremity is supported on the two central toes, instead of on the middle strengthened toe. […] The oldest member of the order is Diacodexis, […] a rabbit-size ungulate”

“Although the number of middle Eocene localities in Europe is quite restricted, we have excellent knowledge of the terrestrial communities of this time thanks to the extraordinary fossiliferous site of Messel, Germany. […] several specimens from Messel retain in their gut their last meal, providing a rare opportunity for testing the teeth-inferred dietary requirements of a number of extinct mammalian groups. […] A dense canopy forest surrounded Messel lake, formed of several tropical and paratropical taxa that today live in Southeast Asia”.

“At the end of the middle Eocene, things began to change in the European archipelago. Several late Paleocene and early Eocene survivors had become extinct […] The last part of the middle Eocene saw a clear change in the structure of the herbivore community as specialized browsing herbivores […] replaced the small to medium-size omnivorous/ frugivorous archaic ungulates of the early Eocene and became the dominant species. […] These changes among the mammalian faunas were most probably a response to the major tectonic transformations occurring at that time and the associated environmental changes. During the middle Eocene, the Indian plate collided with Asia, closing the Tethys Sea north of India. The collision of India and the compression between Africa and Europe formed an active alpine mountain belt along the southern border of Eurasia. In the western Mediterranean, strong compression occurred during the late Eocene, […] leading to the final emergence of the Pyrenees. To the south of the Pyrenees, the sea branch between the Iberian plate and Europe retreated”

“The European terrestrial ecosystems at the end of the Eocene were quite different from those inherited from the Paleocene, which were dominated by archaic, unspecialized groups. In contrast, a diversified fauna of specialized small and large browsing herbivores […] characterized the late Eocene. From our perspective, they looked much more “modern” than those of the early and early-middle Eocene and perfectly adapted to the new late Eocene environmental conditions characterized by the spread of more open habitats.”

“during the Eocene […] Australia and South America were still attached to Antarctica, as the last remnants of the ancient Gondwanan supercontinent. Today’s circumpolar current did not yet exist, and the equatorial South Atlantic and South Pacific waters went closer to the Antarctic coasts, thus transporting heat from the low latitudes to the high southern latitudes. However, this changed during the late Eocene, when a rifting process began to separate Australia from Antarctica. At the beginning of the Oligocene, between 34 and 33 million years ago, the spread between the two continents was large enough to allow a first phase of circumpolar circulation, which restricted the thermal exchange between the low-latitude equatorial waters and the Antarctic waters. A sudden and massive cooling took place, and mean global temperatures fell by about 5°C. […] During a few hundred thousand years (the estimated duration of this early Oligocene glacial episode), the ice sheets expanded and covered extensive areas of Antarctica, particularly in its western regions. […] The onset of Antarctic glaciation and the growing of the ice sheets in western Antarctica provoked an important global sea-level lowering of about 30 m. Several shallow epicontinental seas became continental areas, including those that surrounded the European Archipelago. The Turgai Strait, which during millions of years had isolated the European lands from Asia, vanished and opened a migration pathway for Asian and American mammals to the west. […] The tectonic movements led to the final split of the Tethys Sea into two main seas, the Mediterranean Sea to the south and the Paratethys Sea, the latter covering the formerly open ocean areas of central and eastern Europe. […] After the retreat of the Turgai Strait and the emergence of the Paratethys province, the European Archipelago ceased to exist, and Europe approached its present configuration. The ancient barriers that had prevented Asian faunas from settling in this continental area no longer existed, and a wave of new immigrants entered from the east. This coincided with the trend toward more temperate conditions and the spread of open environments initiated during the late Eocene. Consequently, most of the species that had characterized the middle and late Eocene declined or became completely extinct, replaced by herds of Asian newcomers.”

February 23, 2015 Posted by | Biology, Books, Ecology, Evolutionary biology, Geology, Paleontology, Zoology | Leave a comment

Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe

I’m currently reading this book. It’s quite nice so far, though the title is slightly misleading (I’ve read 82 pages so far and I’ve yet to come across any mammoths, sabertooths or hominids…). I mentioned yesterday that I wanted to cover the systems analysis text in more detail today, but that turned out to be really difficult to do without actually rewriting the book (or at the very least quoting very extensively), something I really don’t want to do. I decided to cover this book instead, though it’s admittedly slightly ‘lazy coverage’. Below I have added some links to stuff he talks about in the book. It’s the sort of book which is reasonably easy to blog, so I’m quite sure I’ll add more detail and context later, especially considering how most people presumably know far more (…okay, well, more) about the lives of the dinosaurs than they do about the lives of their much more recent ancestors, which lived during the Cenozoic.

The book frequently has more information about a given species/genus than does wikipedia’s corresponding article (and there’s stuff in here which wikipedia does not have articles about at all…), and/but I’ve tried to avoid linking to stubs below. Some articles below have decent coverage, but these are in general topics not well covered on wikipedia – I don’t think there’s a single featured article among the articles included. Even so, it’s probably worth having a look at some of the articles below if you’re curious to know which kind of stuff’s covered in this book. Aside from the links, I decided to also include a few pictures from the articles.

Paleocene.
Eocene.
Late Paleocene Thermal Maximum.
Turgai Strait.
Multituberculata.
Leptictidium.
Messel site.
Hyaenodon.

Hyaenodon_Heinrich_Harder
Pantolestidae.
Mixodectidae.
Condylarth.
Arctocyonidae.
Purgatorius.
Dyrosauridae.
Hypsodont.
Gastornis.

Gastornis,_a_large_flightless_bird_from_the_Eocene_of_Wyoming
Plesiadapis.
Pristichampsus.
Pantodonta.
Barylambda_BWMiacids.
Carnassial.
Coryphodon.
Alpine orogeny.
Phenacondus.
Perissodactyla.
Icaronycteris.
Palaeochiropteryx.

800px-Palaeochiropteryx_Paleoart
Adapidae.
Omomyidae.
Artiodactyla.
Palaeotherium.
Chalicotheres.
Eurotamandua.
Strigogyps.

February 13, 2015 Posted by | Biology, Books, Evolutionary biology, Geology, Paleontology, Zoology | Leave a comment

Some links (Open Thread?)

It’s been quite a while since the last time I posted a ‘here’s some interesting stuff I’ve found online’-post, so I’ll do that now even though I actually don’t spend much time randomly looking around for interesting stuff online these days. I added some wikipedia links I’d saved for a ‘wikipedia articles of interest’-post because it usually takes quite a bit of time to write a standard wikipedia post (as it takes time to figure out what to include and what not to include in the coverage) and I figured that if I didn’t add those links here I’d never get around to blogging them.

i. Battle of Dyrrhachium. Found via this link, which has a lot of stuff.

ii. An AMA by someone who claims to have succeeded in faking his own death.

iii. I found this article about the so-called “Einstellung” effect in chess interesting. I’m however not sure how important this stuff really is. I don’t think it’s sub-optimal for a player to spend a significant amount of time in positions like the ones they analyzed on ideas that don’t work, because usually you’ll only have to spot one idea that does to win the game. It’s obvious that one can argue people spend ‘too much’ time looking for a winning combination in positions where by design no winning combinations exist, but the fact of the matter is that in positions where ‘familiar patterns’ pop up winning resources often do exist, and you don’t win games by overlooking those or by failing to spend time looking for them; occasional suboptimal moves in some contexts may be a reasonable price to pay for increasing your likelihood of finding/playing the best/winning moves when those do exist. Here’s a slightly related link dealing with the question of the potential number of games/moves in chess. Here’s a good wiki article about pawn structures, and here’s one about swindles in chess. I incidentally very recently became a member of the ICC, and I’m frankly impressed with the player pool – which is huge and includes some really strong players (players like Morozevich and Tomashevsky seem to play there regularly). Since I started out on the site I’ve already beaten 3 IMs in bullet and lost a game against Islandic GM Henrik Danielsen. The IMs I’ve beaten were far from the strongest players in the player pool, but in my experience you don’t get to play titled players nearly as often as that on other sites if you’re at my level.

iv. A picture of the Andromeda galaxy. A really big picture. Related link here.

v. You may already have seen this one, but in case you have not: A Philosopher Walks Into A Coffee Shop. More than one of these made me laugh out loud. If you like the post you should take a look at the comments as well, there are some brilliant ones there as well.

vi. Amdahl’s law.

vii. Eigendecomposition of a matrix. On a related note I’m currently reading Imboden and Pfenninger’s Introduction to Systems Analysis (which goodreads for some reason has listed under a wrong title, as the goodreads book title is really the subtitle of the book), and today I had a look at the wiki article on Jacobian matrices and determinants for that reason (the book is about as technical as you’d expect from a book with a title like that).

viii. If you’ve been wondering how I’ve found the quotes I’ve posted here on this blog (I’ve posted roughly 150 posts with quotes so far), links like these are very useful.

ix. Geology of the Yosemite area.

February 7, 2015 Posted by | Astronomy, Chess, Geology, History, Mathematics, Open Thread, Random stuff, Wikipedia | Leave a comment

The Voyage of the Beagle (III)

This will be my last post about the book.

I have for some time, probably roughly since the internet problems I had earlier this year were resolved, structured my reading in a way so that I’ll more or less never read fiction/’pure enjoyment’ books while at home. I now only read fiction when I’m out taking walks, and then I limit my book reading to non-fiction while I’m at home. I take long(ish) walks most days so I guess I still finish a fiction book every week or so at the current rate. This change in my reading habits is relevant to my reading of this book because back when I implemented this change, I’d mentally classified the Darwin book as a fiction book/’pure enjoyment’ book – the kind of book I should only be reading while taking walks. It isn’t really fiction, but it is a very enjoyable book to read and in many ways it’s conceptually really much closer to normal fiction stories than it is to a Springer publication about heart disease or mathematics. As it’s often raining in Denmark, it’s often not convenient to take walks while reading ‘paper books’, and my edition of Darwin is a ‘paper book’; I sometimes bring paper books on my walks, but if there’s a risk of rain I’ll usually much prefer to bring my e-reader, which can deal quite well with a few drops of water. A different problem is that I always highlight and write notes in my books, which means that the more interesting and well-written a paper book is, the more inconvenient it is to bring it on walks; I can’t highlight or take notes while walking (I’ve tried, but it doesn’t work), so I have to stop walking every time I come across an interesting sequence which I’d like to highlight or comment upon, of which there are many more in good books than in bad books, and taking a lot of breaks like that can be bothersome in the long run. Some paper books are also too big/heavy to conveniently bring on my walks; however this particular book is not one of those.

What all of above stuff means is of course that for quite a while I didn’t really read very much in this book because I’d settled on not reading it while I was at home, but I also usually had a different book on my e-reader which it was easier and more convenient to bring on my walks. At the end I decided that I should really read the rest of this book because it’s quite good (before I started rereading the book it was on my list of favourites on goodreads, and it still is), and so I decided to read it at home.

The book is really nice. If you liked the quotes I included either in my previous posts about the book and/or in this post, it’s worth considering taking the time to read the book. I may be wrong, but I could easily imagine this being the sort of book that many people might think to themselves that they’ll read when they get old, but then when they reach the pension age they’ll never get around to actually doing it; if this impression is correct, that’s just a damn shame. Reading books like this one or perhaps something like Mark Twain’s The Innocents Abroad (available for free here) will, aside from giving you some enjoyable experiences in the company of good writers, probably make it easier for you to think about the world in a slightly different manner than the one you’re used to.

The book is full of good stuff and so I had to leave out a lot of good stuff in my posts. Below I have added a few more illustrative quotes from the book.

“I heard also of an old lady who, at a dinner at Coquimbo, remarked how wonderfully strange it was that she should have lived to dine in the same room with an Englishman; for she remembered as a girl, that twice, at the mere cry of “Los Ingleses,” every soul, carrying what valuables they could, had taken to the mountains.”

“The connection between earthquakes and the weather has been often disputed: it appears to me to be a point of great interest, which is little understood.”

“My geological examination of the country generally created a good deal of surprise amongst the Chilenos: it was long before they could be convinced that I was not hunting for mines. This was sometimes troublesome: I found the most ready way of explaining my employment, was to ask them how it was that they themselves were not curious concerning earthquakes and volcanos? – why some springs were hot and others cold? – why there were mountains in Chile, and not a hill in La Plata? These bare questions at once satisfied and silenced the greater number; some, however (like a few in England who are a century behind hand), thought that all such inquiries were useless and impious; and that it was quite sufficient that God had thus made the mountains.”

“Our arrival in the offing caused some little apprehension. Peru was in a state of anarchy; and each party having demanded a contribution, the poor town of Iquique was in tribulation, thinking the evil hour was come. The people had also their domestic troubles; a short time before, three French carpenters had broken open, during the same night, the two churches, and stolen all the plate: one of the robbers, however, subsequently confessed, and the plate was recovered. The convicts were sent to Arequipa, which though the capital of this province, is two hundred leagues distant, the government there thought it a pity to punish such useful workmen, who could make all sorts of furniture; and accordingly liberated them. Things being in this state, the churches were again broken open, but this time the plate was not recovered. The inhabitants became dreadfully enraged, and declaring that none but heretics would thus “eat God Almighty,” proceeded to torture some Englishmen, with the intention of afterwards shooting them. At last the authorities interfered, and peace was established.”

“We did not reach the saltpetre-works till after sunset, having ridden all day across an undulating country, a complete and utter desert. The road was strewed with the bones and dried skins of many beasts of burden which had perished on it from fatigue. Excepting the Vultur aura, which preys on the carcasses, I saw neither bird, quadruped, reptile, nor insect. […] I cannot say I liked the very little I saw of Peru: in summer, however, it is said that the climate is much pleasanter. In all seasons, both inhabitants and foreigners suffer from severe attacks of ague. This disease is common on the whole coast of Peru, but is unknown in the interior. The attacks of illness which arise from miasma never fail to appear most mysterious. […] Callao is a filthy, ill-built, small seaport. The inhabitants, both here and at Lima, present every imaginable shade of mixture, between European, Negro, and Indian blood. They appear a depraved, drunken set of people.”

“Of land-birds I obtained twenty-six kinds, all peculiar to the group and found nowhere else, with the exception of one lark-like finch from North America […] The remaining land-birds form a most singular group of finches, related to each other in the structure of their beaks, short tails, form of body and plumage […] The most curious fact is the perfect gradation in the size of the beaks in the different species […] Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends. […] With the exception of a wren with a fine yellow breast, and of a tyrant-flycatcher with a scarlet tuft and breast, none of the birds are brilliantly coloured, as might have been expected in an equatorial district. Hence it would appear probable, that the same causes which here make the immigrants of some peculiar species smaller, make most of the peculiar Galapageian species also smaller, as well as very generally more dusky coloured.” [For more on related topics, see incidentally this previous post of mine].

“As I at first observed, these islands are not so remarkable for the number of the species of reptiles, as for that of the [number of] individuals […] we must admit that there is no other quarter of the world where this Order replaces the herbivorous mammalia in so extraordinary a manner. […] by far the most remarkable feature in the natural history of this archipelago [is] that the different islands to a considerable extent are inhabited by a different set of beings. […] The inhabitants […] state that they can distinguish the tortoises from the different islands; and that they differ not only in size, but in other characters. […] I have strong reasons to suspect that some of the [finch] species of the sub-group Geospiza are confined to separate islands. If the different islands have their representatives of Geospiza, it may help to explain the singularly large number of the species of this sub-group in this one small archipelago, and as a probable consequence of their numbers, the perfectly graduated series in the size of their beaks. […] The distribution of the tenants of this archipelago would not be nearly so wonderful, if, for instance, one island had a mocking-thrush, and a second island some other quite distinct genus,- if one island had its genus of lizard, and a second island another distinct genus, or none whatever; -or if the different islands were inhabited, not by representative species of the same genera of plants, but by totally different genera […]. But it is the circumstance, that several of the islands possess their own species of the tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder. It may be suspected that some of these representative species, at least in the case of the tortoise and of some of the birds, may hereafter prove to be only well-marked races; but this would be of equally great interest to the philosophical naturalist.”

“I was much disappointed in the personal appearance of the [Tahiti] women; they are far inferior in every respect to the men.” [Good luck writing anything like that today and getting it published…] […] After the main discussion was ended, several of the chiefs took the opportunity of asking Captain Fitz Roy many intelligent questions on international customs and laws, relating to the treatment of ships and foreigners. […] This Tahitian parliament lasted for several hours; and when it was over Captain Fitz Roy invited Queen Pomarre to pay the Beagle a visit. […] In the evening four boats were sent for her majesty; the ship was dressed with flags, and the yards manned on her coming on board. She was accompanied by most of the chiefs. The behaviour of all was very proper: they begged for nothing, and seemed much pleased with Captain Fitz Roy’s presents.”

“When I showed the chief a very small bundle, which I wanted carried, it became absolutely necessary for him to take a slave. These feelings of pride are beginning to wear away; but formerly a leading man would sooner have died, than undergone the indignity of carrying the smallest burden.”

“Some time ago, Mr. Bushby suffered a […] serious attack. A chief and a party of men tried to break into his house in the middle of the night, and not finding this so easy, commenced a brisk firing with their muskets. Mr. Bushby was slightly wounded, but the party was at length driven away. Shortly afterwards it was discovered who was the aggressor; and a general meeting of the chiefs was convened to consider the case. It was considered by the New Zealanders as very atrocious, inasmuch as it was a night attack, and that Mrs. Bushby was lying ill in the house: this latter circumstance, much to their honour, being considered in all cases as a protection. The chiefs agreed to confiscate the land of the aggressor to the King of England. The whole proceeding, however, in thus trying and punishing a chief was entirely without precedent. The aggressor, moreover, lost caste in the estimation of his equals and this was considered by the British as of more consequence than the confiscation of his land. […] a chief and a party of men volunteered to walk with us to Waiomio, a distance of four miles. The chief was at this time rather notorious from having lately hung one of his wives and a slave for adultery. When one of the missionaries remonstrated with him he seemed surprised, and said he thought he was exactly following the English method.”

“It is impossible to behold these waves without feeling a conviction that an island, though built of the hardest rock, let it be porphyry, granite, or quartz, would ultimately yield and be demolished by such an irresistible power. Yet these low, insignificant coral-islets stand and are victorious: for here another power, as an antagonist, takes part in the contest. The organic forces separate the atoms of carbonate of lime, one by one, from the foaming breakers, and unite them into a symmetrical structure. Let the hurricane tear up its thousand huge fragments; yet what will that tell against the accumulated labour of myriads of architects at work night and day, month after month? […] We feel surprise when travellers tell us of the vast dimensions of the Pyramids and other great ruins, but how utterly insignificant are the greatest of these, when compared to these mountains of stone accumulated by the agency of various minute and tender animals! This is a wonder which does not at first strike the eye of the body, but, after reflection, the eye of reason.”

“Those who look tenderly at the slave owner, and with a cold heart at the slave, never seem to put themselves into the position of the latter”

December 14, 2014 Posted by | Biology, Books, Evolutionary biology, Geography, Geology, History, Personal, Zoology | Leave a comment

Origin and Evolution of Planetary Atmospheres – Implications for Habitability

I recently finished this book. I gave the book two stars on goodreads, however I also added this comment to the information about the book on my 2014 book list: “Close to three stars, but the poor language of the publication made it difficult for me to justify giving it that rating.” I liked reading the book, but I do not condone sloppy and/or unclear language and this is something I’ll usually punish.

When I started reading the book I’d assumed there might be some overlap with Gale’s book, which I haven’t covered here, but that actually turned out not really to be the case; the two books focus on different things even if a few of the questions they ask are quite similar, and so the coverage of the two books actually don’t much overlap. Most of this was new stuff, which was nice. The book is in my opinion more technical and harder to read than was Gale’s book, but again, they deal with different stuff so I’m not sure how much sense it makes to compare them. Lammer doesn’t shy away from covering relevant math formulas where they might be helpful to improve understanding, and/but some of these are not easy to understand if you do not have a background in physics; you need to know some stuff about things like electromagnetism, thermodynamics, and plasma physics to understand all of the stuff in this book. I didn’t – I certainly didn’t know ‘enough’ – but his coverage is fortunately such that even if you mentally skip a few formulas without really understanding the details of the dynamics they model, you’ll usually still be able to figure out roughly how they work wrt. the specific issue at hand because he also talks about how they work and which conclusions to draw; though you’ll likely still need to look up some unfamiliar terms along the way in order not to be completely confused.

I should make clear that although it may sound from the above as if this is really a rather dull book about mathematical formulas and complicated physics, one thing I find it really hard to term this book is ‘boring’. The book talks about what the Earth was like back when Earth was covered by magma oceans. Freaking magma oceans! It talks about how the Earth was quite likely early on in its ‘lifetime’ (before life on the planet, it should perhaps be noted) covered by a huge hydrogen atmosphere, and how that early atmosphere was blown away by a Sun which was spinning much faster than it does today, bombarding the early proto-atmospheres of the newly formed planets with huge numbers of highly charged particles despite the sun shining ‘less brightly’ back then than it does now. It talks about how a slightly different atmospheric composition back then, with more hydrogen, might have lead to the Earth being unable to get rid of all that hydrogen, most likely leading to the Earth having ended up as a ‘waterworld’ without continents, completely covered by water. It talks about how the Sun slowed down after what was most likely just a few million years, and how it has since then been doing things quite differently from the way it did things in the beginning. Phenomena such as outgassing and impact events are discussed. The book talks about how conditions were different on Mars and Venus from the way they were on Earth, and what role various factors might have played in terms of explaining how the atmospheres got to be the way they are now, and why those planets turned out quite different. The role of gravity, the role of a magnetosphere, which concrete processes lead to loss of (/which) atmospheric components. There’s a lot of stuff in this book, and much of it I found really quite interesting. But it is also hard to read, sometimes hard to understand, and certainly far from always particularly well-written. The topics covered I found quite interesting though.

I was wondering how to cover this book, but I decided early on that given how many things I was looking up along the way it would make a lot of sense to bookmark some relevant links and add them to this post; so below I have added a list of terms and concepts covered in the book. Some of the concepts are much better covered in the book than in the links (the wiki article on atmospheric escape for example has very little stuff on this topic compared to the stuff included in the book about this topic), but in other cases there’s a lot of stuff in the wiki article which was not included in the book (naturally, or it would not have made sense for me to look up stuff there). So the stuff in the links don’t add up to the material covered in the book, but the articles should give you a clue what kind of book this is. Below the list I have added a few quotes from the book. As should be obvious from the number of links, the book has a lot of content despite the relatively low page-count.

Atmosphere of Earth.
Troposphere.
Atmospheric escape.
Hydrodynamic escape.
Maxwell–Boltzmann distribution.
Noachian.
Exosphere.
Outflow channels.
Scale height.
Larmor radius.
Adiabatic process.
Energetic neutral atom.
Magnetopause.
Bow shock.
Lyman series.
Heliosphere.
Roche lobe.
Plasma (physics).
Astrophysical plasma.
Photoionization.
Nebular hypothesis.
Stellar evolution.
Protostar.
Protoplanetary disk
.
Solar wind.
Hydrostatic equilibrium.
Kelvin–Helmholtz instability.
Polar wind.

“As contrasted to meteorology which studies the properties and behavior of the lower atmosphere between the surface and the tropopause where the weather phenomena are generated, aeronomy is a division of atmospheric science that studies physics and chemistry of the upper atmosphere that extends from above the troposphere up to the altitudes where it is modified by the solar wind plasma. […] The central part of [this] monograph presents a detailed discussion of the atmospheric loss mechanisms due to the action of various thermal and non-thermal escape processes for the neutral and ionized particles from a hot, extended atmospheric corona. Scenarios for the formation and evolution of the atmospheres of Earth, Venus, and Mars, that is, the planets orbiting within the habitable zone around the Sun, are considered. A crucial role of the magnetosphere of a planet in protecting its hot, extended, and partially ionized corona from the solar wind erosion is discussed. […] The book presents a brief review of the present state of knowledge of the aeronomy of planetary atmospheres and of their evolution during the lifetime of their host stars by taking into account conventionally accepted concepts, as well as recent observational and theoretical results.”

“the classical concept of the habitable zone and its related questions of what makes a planet habitable is much more complex than having a big rocky body located at the right distance from its host star. […] A careful study of various astrophysical and geophysical aspects indicate that Earth-analogue class I habitats have to be located at the right distance of the habitable zone from their host stars, must lose their protoatmospheres during the right time period, should maintain plate tectonics over the planet’s lifetime, should have nitrogen as the main atmospheric species after the stellar activity decreased to moderate values and finally, the planet’s interior should have developed conditions that an intrinsic strong global magnetic field could evolve.” [I should probably add here that this specific stuff is covered extensively in Gale’s book, but doesn’t make up too much of the coverage of this book].

“The mantle solidification of a magma ocean is a fast process and ends at ∼105 years for Earth-size planets with low volatile contents and at ≤3Myr [million years, US] for planets with higher volatile contents and magma ocean depths of ≤2,000km […] During the magma ocean solidification process, H2O and CO2 molecules can enter the solidifying minerals in relative low quantities [8, 9]. As a result the H2O/CO2 volatiles will degas into dense steam atmospheres […] If the early Earth would have obtained slightly more material from water-rich planetesimals, its CO2 content would have been much higher and Earth’s oceans could have been tens to hundreds of kilometers deep […]. Such environmental conditions would have resulted in a globally covered water world [43, 44] which is surrounded by a Venus-type dense CO2 atmosphere and a hydrogen envelope.” [I tried while reading this to imagine a magma ocean which was something like 2000 kilometers deep, but I failed to do so. Just think about this…]

“There is observational evidence from solar proxies with younger age compared to the present Sun, that during the early history of the Solar System the EUV flux was up to∼100 times larger as it is today […] The evolution of planetary atmospheres can only be understood if one considers that the radiation and particle environment of the Sun or a planet’s host star changed during their life time. The magnetic activity of solar-type stars declines steadily during their evolution on the Zero-Age-Main-Sequence (ZAMS). According to the solar standard model, the Sun’s photospheric luminosity was ∼30 % lower ∼4.5 Gyr ago […] when the Sun arrived on the ZAMS compared to present levels. The observed faster rotation of young stars is responsible for an enhanced magnetic activity and related heating processes in the chromosphere, X-ray emissions are ≥1,000, and EUV, and UV ∼100 and ∼10 times higher compared to today’s solar values. Moreover, the production rate of high-energy particles is orders of magnitude higher at young stars, and from observable stellar mass loss-activity relations one can also expect a much stronger solar/stellar wind during the active stellar phase.”

“The nuclear evolution of the Sun is well known from stellar evolutionary theory and backed by helioseismological observations of the internal solar structure [10]. The results of these evolutionary solar models, indicate that the young Sun was ∼10% cooler and ∼15% smaller compared to the modern Sun ∼4.6Gyr ago. According to the solar standard model, due to accelerating nuclear reactions in the Sun’s core, the Sun is a slowly evolving variable G-type star that has undergone an ∼30% increase in luminosity over the past ∼4.5Gyr. […] the outward flowing plasma carries away angular momentum from the star [which explains] the observed spin-down to slower rotation of young stars after their arrival at the ZAMS [the book mentions elsewhere that it’s been estimated based on observations of other star systems that the young sun was rotating more than 10 times as fast as it does now]. […] the early Earth may have lost during [the first 100 million years] an amount of hydrogen equivalent of ∼20EOs [Earth Oceans] thermally […] after the loss of [a large amount of the original steam atmosphere,] the Earth’s atmosphere environment near the surface reached the critical temperature of ∼650 K. After reaching this temperature the remaining H2O-vapor of ∼1EO could condense and collapsed into the liquid water ocean [84]. Additional amount[s] of water could have been delivered also continuously via impacts, but the bulk of the early Earth’s initial water inventory is most likely a by-product of a condensed fraction of the catastrophically outgassed steam atmosphere. […] One should […] note that in the case of the early Earth due to the Moon forming impact a fraction of ≤30% of atmosphere could have also been lost to space [113].”

“The present average atmospheric mass loss of hydrogen, oxygen, and nitrogen ions from the Earth is ∼ 1.3 × 103 g s-1

“The first protoatmosphere will be captured and accumulated hydrogen- and helium-rich gas envelopes from the nebula. Depending on the planetary formation time, the nebula dissipation time, the numbers of additional planets including gas giants in the system, the protoplanet’s gravity, its orbit location, and the host star’s radiation and plasma environment terrestrial planets may capture tens or even several hundreds of the Earth ocean equivalent amounts of hydrogen around its rocky core.
The second protoatmosphere depends on the initial volatile content of the protoplanet when accretion finished. During the magma ocean solidification […] steam atmospheres with surface pressures ranging from∼100 to several 104 bar can be catastrophically outgassed.
Finally, secondary atmospheres will be produced by tectonic activity such as volcanos and by the delivery of volatiles via large impacts. The origin and initial state of a planet’s protoatmosphere, therefore, determines a planet’s atmospheric evolution and finally if the planet will evolve to an Earth-analog class I habitat or not. […] The efficiency of the solar/stellar forcing is essentially inversely proportional to the square of the distance to the planet’s host star. From that, it follows that the closer a planet orbits around its host star, the more efficient are the atmospheric escape processes. The main effects caused by the stellar radiation and plasma environment on the atmospheres of an effected planet are to ionize, chemically modify, heated, expand, and slowly erode the upper atmosphere throughout the lifetime of a planet. The highest thermal and non-thermal atmospheric escape rates are obtained during the early active phase of the planet’s host star […] Besides the orbital location, a planet’s gravity constitutes an additional major protection mechanism especially for thermal escape of its atmosphere, while the nonthermal escape processes are affected on a weaker scale.”

December 11, 2014 Posted by | Astronomy, Books, Geology, Physics | Leave a comment

The Voyage of the Beagle (II)

As earlier mentioned I’ve recently been rereading this book.

I have added some observations and quotes from the book below.

“The river, though it has so little power in transporting even inconsiderable fragments, yet in the lapse of ages might produce by its gradual erosion an effect of which it is difficult to judge the amount. But in this case, independently of the insignificance of such an agency, good reasons can be assigned for believing that this valley was formerly occupied by an arm of the sea. […] If I had space I could prove that South America was formerly here cut off by a strait, joining the Atlantic and Pacific oceans, like that of Magellan. But it may yet be asked, how has the solid basalt been moved? Geologists formerly would have brought into play, the violent action of some overwhelming debacle; but in this case such a supposition would have been quite inadmissible; because, the same step-like plains with existing seashells lying on their surface, which front the long line of the Patagonian coast, sweep up on each side of the valley of Santa Cruz. No possible action of any flood could thus have modelled the land, either within the valley or along the open coast; and by the formation of such step-like plains or terraces the valley itself had been hollowed out. Although we know that there are tides, which run within the Narrows of the Strait of Magellan at the rate of eight knots an hour, yet we must confess that it makes the head almost giddy to reflect on the number of years, century after century, which the tides, unaided by a heavy surf, must have required to have corroded so vast an area and thickness of solid basaltic lava. Nevertheless, we must believe that the strata undermined by the waters of this ancient strait, were broken up into huge fragments, and these lying scattered on the beach, were reduced first to smaller blocks, then to pebbles and lastly to the most impalpable mud, which the tides drifted far into the Eastern or Western Ocean.”

“On March 1st, 1833, and again on March 16th, 1834, the Beagle anchored in Berkeley Sound, in East Falkland Island. […] After the possession of these miserable islands had been contested by France, Spain, and England, they were left uninhabited. The government of Buenos Ayres then sold them to a private individual, but likewise used them, as old Spain had done before, for a penal settlement. England claimed her right and seized them. The Englishman who was left in charge of the flag was consequently murdered [I’m not sure why, but this sentence incidentally reminded me of this comic]. A British officer was next sent, unsupported by any power. And when we arrived, we found him in charge of a population, of which rather more than half were runaway rebels and murderers.”

“The geological structure of these islands is in most respects simple. The lower country consists of clay-slate and sandstone, containing fossils, very closely related to, but not identical with, those found in the Silurian formations of Europe; the hills are formed of white granular quartz rock. The strata of the latter are frequently arched with perfect symmetry, and the appearance of some of the masses is in consequence most singular. Pernety[8] has devoted several pages to the description of a Hill of Ruins, the successive strata of which he has justly compared to the seats of an amphitheatre. The quartz rock must have been quite pasty when it underwent such remarkable flexures without being shattered into fragments. As the quartz insensibly passes into the sandstone, it seems probable that the former owes its origin to the sandstone having been heated to such a degree that it became viscid, and upon cooling crystallized. While in the soft state it must have been pushed up through the overlying beds.” (This is one neat illustration of the fact that it’s not like people didn’t know anything about geology at this point in time or didn’t have any ideas, even if plate tectonics is still very far away – there’s actually a lot more stuff on this topic later on in the book, for example when Darwin talks about an earthquake (“It is generally thought that this has been the worst earthquake ever recorded in Chile”) which happened in Chile while he was in the area. I may or may not come back to this in my third and presumably last post about the book).

“In the morning the Captain sent a party to communicate with the Fuegians. When we came within hail, one of the four natives who were present advanced to receive us, and began to shout most vehemently, wishing to direct us where to land. When we were on shore the party looked rather alarmed, but continued talking and making gestures with great rapidity. It was without exception the most curious and interesting spectacle I ever beheld: I could not have believed how wide was the difference between savage and civilized man: It is greater than between a wild and domesticated animal, inasmuch as in man there is greater power of improvement. […] Their attitudes were abject, and the expression of their countenance distrustful, surprised, and startled. After we had presented them with some scarlet cloth, which they immediately tied round their necks, they became good friends. […] I have not as yet noticed [meaning in this context: mentioned, US] the Fuegians whom we had on board. During the former voyage of the Adventure and Beagle in 1826 to 1830, Captain Fitz Roy seized on a party of natives, as hostages for the loss of a boat, which had been stolen, to the great jeopardy of a party employed on the survey; and some of these natives, as well as a child whom he bought for a pearl-button, he took with him to England, determining to educate them and instruct them in religion at his own expense. To settle these natives in their own country, was one chief inducement to Captain Fitz Roy to undertake our present voyage; and before the Admiralty had resolved to send out this expedition, Captain Fitz Roy had generously chartered a vessel, and would himself have taken them back.”

“While going one day on shore near Wollaston Island, we pulled alongside a canoe with six Fuegians. These were the most abject and miserable creatures I anywhere beheld. On the east coast the natives, as we have seen, have guanaco cloaks, and on the west they possess seal-skins. Amongst these central tribes the men generally have an otter-skin, or some small scrap about as large as a pocket-handkerchief, which is barely sufficient to cover their backs as low down as their loins. It is laced across the breast by strings, and according as the wind blows, it is shifted from side to side. But these Fuegians in the canoe were quite naked, and even one full-grown woman was absolutely so. It was raining heavily […] Viewing such men, one can hardly make one’s self believe that they are fellow-creatures, and inhabitants of the same world. It is a common subject of conjecture what pleasure in life some of the lower animals can enjoy; how much more reasonably the same question may be asked with respect to these barbarians! At night, five or six human beings, naked and scarcely protected from the win and rain of this tempestuous climate, sleep on the wet ground coiled up like animals. […] They often suffer from famine […] The different tribes when at war are cannibals. From the concurrent, but quite independent evidence of the boy taken by Mr. Low, and of Jemmy Button, it is certainly true, that when pressed in winter by hunger, they kill and devour their old women before they kill their dogs: the boy, being asked by Mr. Low why they did this, answered, “Doggies catch otters, old women no.” This boy described the manner in which they are killed by being held over smoke and thus choked; he imitated their screams as a joke, and described the parts of their bodies which are best to eat. Horrid as such a death by the hands of their friends and relatives must be, the fears of the old women, when hunger begins to press, are more painful to think of; we are told that they often run away into the mountains, but that they are pursued by the men and brought back […] the husband is to the wife a brutal master to a laborious slave.”

“Few if any of these natives [these are incidentally not the same natives as the ones described above, US] could ever have seen a white man […] They were very inoffensive as long as they were few in numbers, but in the morning (21st) being joined by others they showed symptoms of hostility, and we thought that we should have come to a skirmish. An European labours under great disadvantages when treating with savages like these, who have not the least idea of the power of firearms. In the very act of levelling his musket he appears to the savage far inferior to a man armed with a bow and arrow, a spear, or even a sling. Nor is it easy to teach them our superiority except by striking a fatal blow. Like wild beast, they do not appear to compare numbers; for each individual, if attacked, instead of retiring, will endeavour to dash your brains out with a stone, as certainly as a tiger under similar circumstances would tear you.”

“We slept at the gold-mines of Yaquil, which are worked by Mr. Nixon, an American gentleman […] When we arrived at the mine, I was struck by the pale appearance of many of the men, and inquired from Mr. Nixon respecting their condition. The mine is 450 feet deep, and each man brings up about 200 pounds weight of stone. With this load they have to climb up the alternate notches cut in the trunks of trees, placed in a zig-zag line up the shaft. Even beardless young men, eighteen and twenty years old, with little muscular development of their bodies (they are quite naked excepting drawers) ascend with this great load from nearly the same depth. A strong man, who is not accustomed to this labour, perspires most profusely, with merely carrying up his own body. With this very severe labour, they live entirely on boiled beans and bread. They would prefer having bread alone; but their masters, finding that they cannot work so hard upon this, treat them like horses, and make them eat the beans. […] They leave the mine only once in three weeks; when they stay with their families for two days. One of the rules of this mine sounds very harsh, but answers pretty well for the master. The only method of stealing gold is to secrete pieces of the ore, and take them out as occasion may offer. Whenever the major-domo finds a lump thus hidden, its full value is stopped out of the wages of all the men; who thus, without they all combine, are obliged to keep watch over each other. […] Bad as the above treatment of the miners appears, it is gladly accepted of by them; for the condition of the labouring agriculturalists is much worse. Their wages are lower, and they live almost exclusively on beans. […] extreme poverty is very common among the labouring classes in this country.”

“The poverty of the place [Chiloe Island – in Chile, US] may be conceived from the fact, that although containing some hundreds of inhabitants, one of our party was unable anywhere to purchase either a pound of sugar or an ordinary knife. No individual possessed either a watch or a clock; and an old man, who was supposed to have a good idea of time, was employed to strike the church bells by guess. […] There is also a great deficiency of a circulating medium. I have seen a man bringing on his back a bag of charcoal, with which to buy some trifle, and another carrying a plank to exchange for a bottle of wine. Hence every tradesman must also be a merchant, and again sell the goods which he takes in exchange. […] In all parts of Chiloe and Chonos, two very strange birds occur […] One is called by the inhabitants “Cheucau” (Pteroptochos rubecula): it frequents the most gloomy and retired spots within the damp forests. Sometimes, although its cry may be heard close at hand, let a person watch ever so attentively he will not see the cheucau; at other times, let him stand motionless and the red-breasted little bird will approach within a few feet in the most familiar manner. […] The cheucau is held in superstitious fear by the Chilotans, on account of its strange and varied cries. There are three very distinct cries: one is called “chiduco,” and is an omen of good; another, “huitreu,” which is extremely unfavourable; and a third, which I have forgotten. These words are given in imitation of the noises; and the natives are in some things absolutely governed by them. The Chilotans assuredly have chosen a most comical little creature for their prophet.”

 

December 3, 2014 Posted by | Books, Geology, History | Leave a comment

Wikipedia articles of interest

(A minor note: These days when I’m randomly browsing wikipedia and not just looking up concepts or terms found in the books I read, I’m mostly browsing the featured content on wikipedia. There’s a lot of featured stuff, and on average such articles more interesting than random articles. As a result of this approach, all articles covered in the post below are featured articles. A related consequence of this shift may be that I may cover fewer articles in future wikipedia posts than I have in the past; this post only contains five articles, which I believe is slightly less than usual for these posts – a big reason for this being that it sometimes takes a lot of time to read a featured article.)

i. Woolly mammoth.

Ice_age_fauna_of_northern_Spain_-_Mauricio_Antón

“The woolly mammoth (Mammuthus primigenius) was a species of mammoth, the common name for the extinct elephant genus Mammuthus. The woolly mammoth was one of the last in a line of mammoth species, beginning with Mammuthus subplanifrons in the early Pliocene. M. primigenius diverged from the steppe mammoth, M. trogontherii, about 200,000 years ago in eastern Asia. Its closest extant relative is the Asian elephant. […] The earliest known proboscideans, the clade which contains elephants, existed about 55 million years ago around the Tethys Sea. […] The family Elephantidae existed six million years ago in Africa and includes the modern elephants and the mammoths. Among many now extinct clades, the mastodon is only a distant relative of the mammoths, and part of the separate Mammutidae family, which diverged 25 million years before the mammoths evolved.[12] […] The woolly mammoth coexisted with early humans, who used its bones and tusks for making art, tools, and dwellings, and the species was also hunted for food.[1] It disappeared from its mainland range at the end of the Pleistocene 10,000 years ago, most likely through a combination of climate change, consequent disappearance of its habitat, and hunting by humans, though the significance of these factors is disputed. Isolated populations survived on Wrangel Island until 4,000 years ago, and on St. Paul Island until 6,400 years ago.”

“The appearance and behaviour of this species are among the best studied of any prehistoric animal due to the discovery of frozen carcasses in Siberia and Alaska, as well as skeletons, teeth, stomach contents, dung, and depiction from life in prehistoric cave paintings. […] Fully grown males reached shoulder heights between 2.7 and 3.4 m (9 and 11 ft) and weighed up to 6 tonnes (6.6 short tons). This is almost as large as extant male African elephants, which commonly reach 3–3.4 m (9.8–11.2 ft), and is less than the size of the earlier mammoth species M. meridionalis and M. trogontherii, and the contemporary M. columbi. […] Woolly mammoths had several adaptations to the cold, most noticeably the layer of fur covering all parts of the body. Other adaptations to cold weather include ears that are far smaller than those of modern elephants […] The small ears reduced heat loss and frostbite, and the tail was short for the same reason […] They had a layer of fat up to 10 cm (3.9 in) thick under the skin, which helped to keep them warm. […] The coat consisted of an outer layer of long, coarse “guard hair”, which was 30 cm (12 in) on the upper part of the body, up to 90 cm (35 in) in length on the flanks and underside, and 0.5 mm (0.020 in) in diameter, and a denser inner layer of shorter, slightly curly under-wool, up to 8 cm (3.1 in) long and 0.05 mm (0.0020 in) in diameter. The hairs on the upper leg were up to 38 cm (15 in) long, and those of the feet were 15 cm (5.9 in) long, reaching the toes. The hairs on the head were relatively short, but longer on the underside and the sides of the trunk. The tail was extended by coarse hairs up to 60 cm (24 in) long, which were thicker than the guard hairs. It is likely that the woolly mammoth moulted seasonally, and that the heaviest fur was shed during spring.”

“Woolly mammoths had very long tusks, which were more curved than those of modern elephants. The largest known male tusk is 4.2 m (14 ft) long and weighs 91 kg (201 lb), but 2.4–2.7 m (7.9–8.9 ft) and 45 kg (99 lb) was a more typical size. Female tusks averaged at 1.5–1.8 m (4.9–5.9 ft) and weighed 9 kg (20 lb). About a quarter of the length was inside the sockets. The tusks grew spirally in opposite directions from the base and continued in a curve until the tips pointed towards each other. In this way, most of the weight would have been close to the skull, and there would be less torque than with straight tusks. The tusks were usually asymmetrical and showed considerable variation, with some tusks curving down instead of outwards and some being shorter due to breakage.”

“Woolly mammoths needed a varied diet to support their growth, like modern elephants. An adult of six tonnes would need to eat 180 kg (397 lb) daily, and may have foraged as long as twenty hours every day. […] Woolly mammoths continued growing past adulthood, like other elephants. Unfused limb bones show that males grew until they reached the age of 40, and females grew until they were 25. The frozen calf “Dima” was 90 cm (35 in) tall when it died at the age of 6–12 months. At this age, the second set of molars would be in the process of erupting, and the first set would be worn out at 18 months of age. The third set of molars lasted for ten years, and this process was repeated until the final, sixth set emerged when the animal was 30 years old. A woolly mammoth could probably reach the age of 60, like modern elephants of the same size. By then the last set of molars would be worn out, the animal would be unable to chew and feed, and it would die of starvation.[53]

“The habitat of the woolly mammoth is known as “mammoth steppe” or “tundra steppe”. This environment stretched across northern Asia, many parts of Europe, and the northern part of North America during the last ice age. It was similar to the grassy steppes of modern Russia, but the flora was more diverse, abundant, and grew faster. Grasses, sedges, shrubs, and herbaceous plants were present, and scattered trees were mainly found in southern regions. This habitat was not dominated by ice and snow, as is popularly believed, since these regions are thought to have been high-pressure areas at the time. The habitat of the woolly mammoth also supported other grazing herbivores such as the woolly rhinoceros, wild horses and bison. […] A 2008 study estimated that changes in climate shrank suitable mammoth habitat from 7,700,000 km2 (3,000,000 sq mi) 42,000 years ago to 800,000 km2 (310,000 sq mi) 6,000 years ago.[81][82] Woolly mammoths survived an even greater loss of habitat at the end of the Saale glaciation 125,000 years ago, and it is likely that humans hunted the remaining populations to extinction at the end of the last glacial period.[83][84] […] Several woolly mammoth specimens show evidence of being butchered by humans, which is indicated by breaks, cut-marks, and associated stone tools. It is not known how much prehistoric humans relied on woolly mammoth meat, since there were many other large herbivores available. Many mammoth carcasses may have been scavenged by humans rather than hunted. Some cave paintings show woolly mammoths in structures interpreted as pitfall traps. Few specimens show direct, unambiguous evidence of having been hunted by humans.”

“While frozen woolly mammoth carcasses had been excavated by Europeans as early as 1728, the first fully documented specimen was discovered near the delta of the Lena River in 1799 by Ossip Schumachov, a Siberian hunter.[90] Schumachov let it thaw until he could retrieve the tusks for sale to the ivory trade. [Aargh!] […] The 1901 excavation of the “Berezovka mammoth” is the best documented of the early finds. It was discovered by the Berezovka River, and the Russian authorities financed its excavation. Its head was exposed, and the flesh had been scavenged. The animal still had grass between its teeth and on the tongue, showing that it had died suddenly. […] By 1929, the remains of 34 mammoths with frozen soft tissues (skin, flesh, or organs) had been documented. Only four of them were relatively complete. Since then, about that many more have been found.”

ii. Daniel Lambert.

Daniel Lambert (13 March 1770 – 21 June 1809) was a gaol keeper[n 1] and animal breeder from Leicester, England, famous for his unusually large size. After serving four years as an apprentice at an engraving and die casting works in Birmingham, he returned to Leicester around 1788 and succeeded his father as keeper of Leicester’s gaol. […] At the time of Lambert’s return to Leicester, his weight began to increase steadily, even though he was athletically active and, by his own account, abstained from drinking alcohol and did not eat unusual amounts of food. In 1805, Lambert’s gaol closed. By this time, he weighed 50 stone (700 lb; 318 kg), and had become the heaviest authenticated person up to that point in recorded history. Unemployable and sensitive about his bulk, Lambert became a recluse.

In 1806, poverty forced Lambert to put himself on exhibition to raise money. In April 1806, he took up residence in London, charging spectators to enter his apartments to meet him. Visitors were impressed by his intelligence and personality, and visiting him became highly fashionable. After some months on public display, Lambert grew tired of exhibiting himself, and in September 1806, he returned, wealthy, to Leicester, where he bred sporting dogs and regularly attended sporting events. Between 1806 and 1809, he made a further series of short fundraising tours.

In June 1809, he died suddenly in Stamford. At the time of his death, he weighed 52 stone 11 lb (739 lb; 335 kg), and his coffin required 112 square feet (10.4 m2) of wood. Despite the coffin being built with wheels to allow easy transport, and a sloping approach being dug to the grave, it took 20 men almost half an hour to drag his casket into the trench, in a newly opened burial ground to the rear of St Martin’s Church.”

“Sensitive about his weight, Daniel Lambert refused to allow himself to be weighed, but sometime around 1805, some friends persuaded him to come with them to a cock fight in Loughborough. Once he had squeezed his way into their carriage, the rest of the party drove the carriage onto a large scale and jumped out. After deducting the weight of the (previously weighed) empty carriage, they calculated that Lambert’s weight was now 50 stone (700 lb; 318 kg), and that he had thus overtaken Edward Bright, the 616-pound (279 kg) “Fat Man of Maldon”,[23] as the heaviest authenticated person in recorded history.[20][24]

Despite his shyness, Lambert badly needed to earn money, and saw no alternative to putting himself on display, and charging his spectators.[20] On 4 April 1806, he boarded a specially built carriage and travelled from Leicester[26] to his new home at 53 Piccadilly, then near the western edge of London.[20] For five hours each day, he welcomed visitors into his home, charging each a shilling (about £3.5 as of 2014).[18][25] […] Lambert shared his interests and knowledge of sports, dogs and animal husbandry with London’s middle and upper classes,[27] and it soon became highly fashionable to visit him, or become his friend.[27] Many called repeatedly; one banker made 20 visits, paying the admission fee on each occasion.[17] […] His business venture was immediately successful, drawing around 400 paying visitors per day. […] People would travel long distances to see him (on one occasion, a party of 14 travelled to London from Guernsey),[n 5] and many would spend hours speaking with him on animal breeding.”

“After some months in London, Lambert was visited by Józef Boruwłaski, a 3-foot 3-inch (99 cm) dwarf then in his seventies.[44] Born in 1739 to a poor family in rural Pokuttya,[45] Boruwłaski was generally considered to be the last of Europe’s court dwarfs.[46] He was introduced to the Empress Maria Theresa in 1754,[47] and after a short time residing with deposed Polish king Stanisław Leszczyński,[44] he exhibited himself around Europe, thus becoming a wealthy man.[48] At age 60, he retired to Durham,[49] where he became such a popular figure that the City of Durham paid him to live there[50] and he became one of its most prominent citizens […] The meeting of Lambert and Boruwłaski, the largest and smallest men in the country,[51] was the subject of enormous public interest”

“There was no autopsy, and the cause of Lambert’s death is unknown.[65] While many sources say that he died of a fatty degeneration of the heart or of stress on his heart caused by his bulk, his behaviour in the period leading to his death does not match that of someone suffering from cardiac insufficiency; witnesses agree that on the morning of his death he appeared well, before he became short of breath and collapsed.[65] Bondeson (2006) speculates that the most consistent explanation of his death, given his symptoms and medical history, is that he had a sudden pulmonary embolism.[65]

iii. Geology of the Capitol Reef area.

Waterpocket_Fold_-_Looking_south_from_the_Strike_Valley_Overlook

“The exposed geology of the Capitol Reef area presents a record of mostly Mesozoic-aged sedimentation in an area of North America in and around Capitol Reef National Park, on the Colorado Plateau in southeastern Utah.

Nearly 10,000 feet (3,000 m) of sedimentary strata are found in the Capitol Reef area, representing nearly 200 million years of geologic history of the south-central part of the U.S. state of Utah. These rocks range in age from Permian (as old as 270 million years old) to Cretaceous (as young as 80 million years old.)[1] Rock layers in the area reveal ancient climates as varied as rivers and swamps (Chinle Formation), Sahara-like deserts (Navajo Sandstone), and shallow ocean (Mancos Shale).

The area’s first known sediments were laid down as a shallow sea invaded the land in the Permian. At first sandstone was deposited but limestone followed as the sea deepened. After the sea retreated in the Triassic, streams deposited silt before the area was uplifted and underwent erosion. Conglomerate followed by logs, sand, mud and wind-transported volcanic ash were later added. Mid to Late Triassic time saw increasing aridity, during which vast amounts of sandstone were laid down along with some deposits from slow-moving streams. As another sea started to return it periodically flooded the area and left evaporite deposits. Barrier islands, sand bars and later, tidal flats, contributed sand for sandstone, followed by cobbles for conglomerate and mud for shale. The sea retreated, leaving streams, lakes and swampy plains to become the resting place for sediments. Another sea, the Western Interior Seaway, returned in the Cretaceous and left more sandstone and shale only to disappear in the early Cenozoic.”

“The Laramide orogeny compacted the region from about 70 million to 50 million years ago and in the process created the Rocky Mountains. Many monoclines (a type of gentle upward fold in rock strata) were also formed by the deep compressive forces of the Laramide. One of those monoclines, called the Waterpocket Fold, is the major geographic feature of the park. The 100 mile (160 km) long fold has a north-south alignment with a steeply east-dipping side. The rock layers on the west side of the Waterpocket Fold have been lifted more than 7,000 feet (2,100 m) higher than the layers on the east.[23] Thus older rocks are exposed on the western part of the fold and younger rocks on the eastern part. This particular fold may have been created due to movement along a fault in the Precambrian basement rocks hidden well below any exposed formations. Small earthquakes centered below the fold in 1979 may be from such a fault.[24] […] Ten to fifteen million years ago the entire region was uplifted several thousand feet (well over a kilometer) by the creation of the Colorado Plateaus. This time the uplift was more even, leaving the overall orientation of the formations mostly intact. Most of the erosion that carved today’s landscape occurred after the uplift of the Colorado Plateau with much of the major canyon cutting probably occurring between 1 and 6 million years ago.”

iv. Problem of Apollonius.

“In Euclidean plane geometry, Apollonius’s problem is to construct circles that are tangent to three given circles in a plane (Figure 1).

396px-Apollonius_problem_typical_solution.svg

Apollonius of Perga (ca. 262 BC – ca. 190 BC) posed and solved this famous problem in his work Ἐπαφαί (Epaphaí, “Tangencies”); this work has been lost, but a 4th-century report of his results by Pappus of Alexandria has survived. Three given circles generically have eight different circles that are tangent to them […] and each solution circle encloses or excludes the three given circles in a different way […] The general statement of Apollonius’ problem is to construct one or more circles that are tangent to three given objects in a plane, where an object may be a line, a point or a circle of any size.[1][2][3][4] These objects may be arranged in any way and may cross one another; however, they are usually taken to be distinct, meaning that they do not coincide. Solutions to Apollonius’ problem are sometimes called Apollonius circles, although the term is also used for other types of circles associated with Apollonius. […] A rich repertoire of geometrical and algebraic methods have been developed to solve Apollonius’ problem,[9][10] which has been called “the most famous of all” geometry problems.[3]

v. Globular cluster.

“A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is derived from the Latin globulus—a small sphere. A globular cluster is sometimes known more simply as a globular.

Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk. Globular clusters are fairly common; there are about 150[2] to 158[3] currently known globular clusters in the Milky Way, with perhaps 10 to 20 more still undiscovered.[4] Large galaxies can have more: Andromeda, for instance, may have as many as 500. […]

Every galaxy of sufficient mass in the Local Group has an associated group of globular clusters, and almost every large galaxy surveyed has been found to possess a system of globular clusters.[8] The Sagittarius Dwarf galaxy and the disputed Canis Major Dwarf galaxy appear to be in the process of donating their associated globular clusters (such as Palomar 12) to the Milky Way.[9] This demonstrates how many of this galaxy’s globular clusters might have been acquired in the past.

Although it appears that globular clusters contain some of the first stars to be produced in the galaxy, their origins and their role in galactic evolution are still unclear.”

October 23, 2014 Posted by | Astronomy, Biology, Ecology, Geography, Geology, History, Mathematics, Paleontology, Wikipedia, Zoology | Leave a comment

An Introduction to Tropical Rain Forests (II)

First an update on the issues I mentioned earlier this week: I had a guy come by and ‘fix the internet problem’ yesterday. Approximately an hour after he left I lost my connection, and it was gone for the rest of the day. I have internet now. If the problem is not solved by a second visit on Monday (they’ll send another guy over), the ISP just lost a customer – I’ll give them no more chances, I can’t live like this. The uncertainty is both incredibly stressful and frankly infuriating. I actually lost internet while writing this post. Down periods seem completely random and may last from 5 minutes to 12 hours. I’m much more dependent on the internet than are most people in part because most of my social interaction with others takes place online.

I’ve read four Christie novels within the last week and I finished The Gambler by Dostoyevsky earlier today – in case you were wondering why I’ve suddenly started reading a lot of fiction, the answer is simple: I’m awake for 16+ hours each day, and if I can’t go online to relax during my off hours I have to find some other way to distract-/enjoy-/whatever myself. Novels are one of the tools I’ve employed.

The internet issue is more important than the computer issue also in terms of the blogging context; the computer I’m using at the moment is unreliable, but seems to cause a limited amount of trouble when I’m doing simple stuff like blogging.

Okay, on to the book. I was rather harsh in my first post, but I did also mention that it had a lot of good stuff. I’ve included some of that stuff in this post below.

“Forests, because of their stature, have internal microclimates that differ from the general climate outside the canopy. […] In general terms, it is cool, humid, and dark near the floor of a mature patch of forest, progressively altering upwards to the canopy top. Different plants and animal species have specialized to the various forest interior microclimates […] Night is the winter of the tropics, because the diurnal range of mean daily temperature exceeds the annual range and is greater in drier months. […] Rain forests develop where every month is wet (with 100 mm rainfal or more), or there are only short dry periods which occur mainly as unpredictable spells lasting only a few days or weeks. Where there are several dry months (60 mm rainfal or less) of regular occurence, monsoon forests exist. Outside Asia these are usually called tropical seasonal forests. […] To the biologist […] there are major differences, and this book is about tropical rain forests, those which occur in the everwet (perhumid) climates, with only passing mention of monsoon forests.”

“Tropical rain forests occur in all three tropical land areas […]. Most extensive are the American or neotropical rain forests, about half the global total, 4 x 106 km2 in area, and one-sixth of the total broad-leaf forest of the world. […] The second largest block of tropical rain forest occurs in the Eastern tropics, and is estimated to cover 2.5 x 106 km2. It is centred on the Malay archipelago, the region known to botanists as Malesia. Indonesia[25] occupies most of the archipelago and is second to Brazil in the amount of rain forest it possesses. […] Africa has the smallest block of tropical rain forest, 1.8 x 106 km2. This is centred on the Congo basin, reaching from the high mountains at its eastern limit westwards to the Atlantic Ocean, with outliers in East Africa. […] Outside the Congo core the African rain forests have been extensively destroyed.”

“It is now believed that about half the world’s species occur in tropical rain forests although they only occupy about seven per cent of the land area. […] Just how many species the world’s rain forests contain is still […] only a matter of rough conjecture. For mammals, birds, and other larger animals there are roughly twice as many species in tropical regions as temperate ones […]. These groups are fairly well studied, insects and other invertebrates much less so […] The humid tropics are extremely rich in plant species. Of the total of approximately 250 000 species of flowering plants in the world, about two-thirds (170 000) occur in the tropics. Half of these are in the New World south of the Mexico/US frontier, 21 000 in tropical Africa (plus 10 000 in Madagascar) and 50 000 in tropical and subtropical Asia, with 36 000 in Malesia. […] There are similarities, especially at family level, between all three blocks of tropical rain forest, but there are fewer genera in common and not many species. […] In flora Africa has been called ‘the odd man out’;[52] there are fewer families, fewer genera, and fewer species in her rain forests than in either America or Asia. For example, there are 18 genera and 51 species of native palms on Singapore island,[53] as many as on the whole of mainland Africa (15 genera, 50 species) […] There are also differences within each rain forest region. […] meaningful discussions of species richness must specify scale.[60] For example, we may usefully compare richness within rain forests by counting tree species on plots of c. 1 ha. This within-community diversity has been called alpha diversity. At the other extreme we can record species richness of a whole landscape made up of several communities, and this has been called gamma diversity. The fynbos is very rich with 8500 species on 89 000 km2. It is made up of a mosaic of different floristic communities, each of which has rather few species. That is to say fynbos has low alpha and high gamma diversity. Within a single floristic community species replace each other from place to place. This gives a third component to richness, known as beta diversity. For example, within lowland rain forest there are differences in species within a single community between ridges, hillsides, and valleys.”

“Most rain forest trees […] exhibit intermittent shoot growth […] The intermittent growth of the shoot tips is seldom reflected by growth rings in the wood, and where it is these are not annual and often not annular either. Rain forest trees, unlike those of seasonal climates, cannot be aged by counting wood rings […] tree age cannot be measured directly. It has [also] been found that the fastest growing juvenile trees in a forest are the ones most likely to succeed, so growth rates averaged from a number of stems are misleading. […] we have very little reliable information on how long trees can live. […] Most of the root biomass is in the top 0.3 m or so of the soil and there is sometimes a concentration or root mat at the surface. […] Roots up to 2 mm in diameter form 20-50 per cent of the total root biomass[79] and their believed rapid turnover is probably a significant part of ecosystem nutrient cycles”

“Besides differences between the three tropical regions there are other differences within them. One major pattern is that within the African and American rain forests there are areas of especially high species richness, set like islands in a sea of relative poverty. […] No such patchiness has been detected in Asia, where the major pattern is set by Wallace’s Line, one of the sharpest zoogeographical boundaries in the world and which delimits the continental Asian faunas from the Australasian […]. These patterns are now realized to have explanations based on Earth[‘s] history […] Gondwanaland and Laurasia were [originally] separated by the great Tethys Ocean. Tethys was closed by the northwards movement of parts of Gondwanaland […]. First Africa and then India drifted north and collided with the southern margin of Laurasia. Further east the continental plate which comprised Antarctica/Australia/southern New Guinea moved northwards, broke in two leaving Antarctica behind, and, as a simplification, collided with the southeast extremity of Laurasia, at about 15 million years ago, the mid-Miocene; this created the Malay archipelago (Malesia) as it exists today. Both super-continents had their own sets of plants and animals. […] Western and eastern Malesia have very different animals, demarcated by a very sharp boundary, Wallace’s line. […] the evolution of the Malay archipelago was in fact more complex than a single collision.[145] Various shards progressively broke off Gondwana from the Jurassic onwards, drifted northwards, and became embedded in what is now continental Asia […]  The climate of the tropics has been continually changing. The old idea of fixity is quite wrong; climatic changes have had profound influences on species ranges.”

“Most knowledge about past climates is for the last 2 million years, the Quaternary period, during which there has been repeated alternation at high latitudes near the poles between Ice Ages or Glacial periods and Interglacials. During Glacial periods tropical climates were slightly cooler and drier, with lower and more seasonal rainfall. During these times rain forests became less extensive and seasonal forests expanded. Most of the Quaternary was like that; present-day climates are extreme and not typical of the period as a whole. Today we live at the height of an Interglacial. […] At the Glacial maxima sea levels were lower by as much as 180 m […] Sea surface temperature was cooler than today, by 5 ° C or more[147] at 18 000 BP in the tropics. […] Rain forests were more extensive than at any time in the Quaternary during the early Pliocene, parts of the Miocene, and especially the early Eocene; so these were all warm periods. Then, in the late Tertiary, fluctuations similar to those of the Quaternary occurred. […] Africa [as mentioned] has a much poorer flora than the other two rain forest regions.[152] This is believed to be because it was much more strongly dessicated during the Tertiary. […] Australia too suffered strong Tertiary dessication. At that time its mesic vegetation became mainly confined to the eastern seaboard. The strip of tropical rain forests found today in north Queensland is only 2-30 km wide and is of particular interest because it contains the relicts of the old mesic flora. This includes the ancestors from which many modern Australian species adapted to hot dry climates are believed to have evolved […] New Caledonia is a shard of Gondwanaland which drifted away eastwards from northeast Australia starting in the Upper Cretaceous 82 million BP. Because it is an island its vegetation has suffered less from the drier Glacial climates so more of the old flora has survived. The lands bordering the western Pacific have the greatest concentration of primitive flowering plants found anywhere […] It is most likely that they survived here as relicts.”

“rain forests have waxed and waned in extent during the Quaternary, and probably in the Tertiary too, and are not the ancient and immutable bastions where life originated which populist writings still sometimes suggest. In the present Interglacial they are as extensive as they have ever been, or nearly so. At glacial maxima lowland rain forests are believed to have contracted and only to have persisted in places where conditions remained favourable for them, as patches surrounded by tropical seasonal forests, like islands set in a sea. In subsequent Interglacials, as perhumid conditions returned, the rain forests expanded out of these patches, which have come to be called Pleistocene refugia. In the late 1960s it was shown that within Amazonia birds have areas of high species endemism and richness which are surrounded by relatively poorer areas. The same was soon demonstrated for lizards.[153] Subsequently many groups of animals have been shown to exhibit such patchiness […] The centres of concentration more or less coincide with each other […] These loci overlap with areas that geoscientific evidence suggests retained rain forest during Pleistocene glaciations […] In the African rain forests four groups of loci of species richness and endemism are now recognized […] Most parts of Malesia today are about as equally rich in species, including endemics, as the Pleistocene refugia of Africa and America. At the Glacial maxima the Sunda and Sahul continental shelves were exposed by falling sealevel. Rain forests were likely to have become confined to the more mountaineous places where there was more, orographic, rain. The main development of seasonal forests in this region is likely to have been on the newly exposed lowlands, and when sea-level rose again at the next Interglacial these and the physical signs of seasonal climates […] were drowned. The parts of Malesia that are above sea-level today probably remained, largely perhumid and covered by rain forest, which explains their extreme species richness and their lack of geoscientific evidence of seasonal past climates. […] Present-day lowland rain forest communities consist of plant and animal species that have survived past climatic vicissitudes or have immigrated since the climate ameliorated. Thus many species co-exist today as a result of historical chance, not because they co-evolved together. Their communities are neither immutable nor finely tuned. This point is of great importance to the ideas scientists have expressed concerning plant-animal interactions […] Those parts of the world’s tropical rain forests that are most rich in species are those that the evidence shows have been the most stable, where species have evolved and continued to accumulate with the passage of time without episodes of extinction caused by unfavourable climatic periods. This is similar to the pattern observed in other forest biomes”

September 20, 2014 Posted by | Biology, Books, Botany, climate, Ecology, Evolutionary biology, Geography, Geology | Leave a comment

Wikipedia articles of interest

i. Dodo (featured article).

“The dodo (Raphus cucullatus) is an extinct flightless bird that was endemic to the island of Mauritius, east of Madagascar in the Indian Ocean. Its closest genetic relative was the also extinct Rodrigues solitaire, the two forming the subfamily Raphinae of the family of pigeons and doves. […] Subfossil remains show the dodo was about 1 metre (3.3 feet) tall and may have weighed 10–18 kg (22–40 lb) in the wild. The dodo’s appearance in life is evidenced only by drawings, paintings and written accounts from the 17th century. Because these vary considerably, and because only some illustrations are known to have been drawn from live specimens, its exact appearance in life remains unresolved. Similarly, little is known with certainty about its habitat and behaviour.”

“The first recorded mention of the dodo was by Dutch sailors in 1598. In the following years, the bird was hunted by sailors, their domesticated animals, and invasive species introduced during that time. The last widely accepted sighting of a dodo was in 1662. Its extinction was not immediately noticed, and some considered it to be a mythical creature. In the 19th century, research was conducted on a small quantity of remains of four specimens that had been brought to Europe in the early 17th century. Among these is a dried head, the only soft tissue of the dodo that remains today. Since then, a large amount of subfossil material has been collected from Mauritius […] The dodo was anatomically similar to pigeons in many features. […] The dodo differed from other pigeons mainly in the small size of the wings and the large size of the beak in proportion to the rest of the cranium. […] Many of the skeletal features that distinguish the dodo and the Rodrigues solitaire, its closest relative, from pigeons have been attributed to their flightlessness. […] The lack of mammalian herbivores competing for resources on these islands allowed the solitaire and the dodo to attain very large sizes.[19]” [If the last sentence sparked your interest and/or might be something about which you’d like to know more, I have previously covered a great book on related topics here on the blog]

“The etymology of the word dodo is unclear. Some ascribe it to the Dutch word dodoor for “sluggard”, but it is more probably related to Dodaars, which means either “fat-arse” or “knot-arse”, referring to the knot of feathers on the hind end. […] The traditional image of the dodo is of a very fat and clumsy bird, but this view may be exaggerated. The general opinion of scientists today is that many old European depictions were based on overfed captive birds or crudely stuffed specimens.[44]

“Like many animals that evolved in isolation from significant predators, the dodo was entirely fearless of humans. This fearlessness and its inability to fly made the dodo easy prey for sailors.[79] Although some scattered reports describe mass killings of dodos for ships’ provisions, archaeological investigations have found scant evidence of human predation. […] The human population on Mauritius (an area of 1,860 km2 or 720 sq mi) never exceeded 50 people in the 17th century, but they introduced other animals, including dogs, pigs, cats, rats, and crab-eating macaques, which plundered dodo nests and competed for the limited food resources.[37] At the same time, humans destroyed the dodo’s forest habitat. The impact of these introduced animals, especially the pigs and macaques, on the dodo population is currently considered more severe than that of hunting. […] Even though the rareness of the dodo was reported already in the 17th century, its extinction was not recognised until the 19th century. This was partly because, for religious reasons, extinction was not believed possible until later proved so by Georges Cuvier, and partly because many scientists doubted that the dodo had ever existed. It seemed altogether too strange a creature, and many believed it a myth.”

Some of the contemporary accounts and illustrations included in the article, from which behavioural patterns etc. have been inferred, I found quite depressing. Two illustrative quotes and a contemporary engraving are included below:

“Blue parrots are very numerous there, as well as other birds; among which are a kind, conspicuous for their size, larger than our swans, with huge heads only half covered with skin as if clothed with a hood. […] These we used to call ‘Walghvogel’, for the reason that the longer and oftener they were cooked, the less soft and more insipid eating they became. Nevertheless their belly and breast were of a pleasant flavour and easily masticated.[40]

“I have seen in Mauritius birds bigger than a Swan, without feathers on the body, which is covered with a black down; the hinder part is round, the rump adorned with curled feathers as many in number as the bird is years old. […] We call them Oiseaux de Nazaret. The fat is excellent to give ease to the muscles and nerves.[7]

640px-Jacht_op_dodo's_door_Willem_van_West-Zanen_uit_1602

ii. Armero tragedy (featured).

“The Armero tragedy […] was one of the major consequences of the eruption of the Nevado del Ruiz stratovolcano in Tolima, Colombia, on November 13, 1985. After 69 years of dormancy, the volcano’s eruption caught nearby towns unaware, even though the government had received warnings from multiple volcanological organizations to evacuate the area when volcanic activity had been detected in September 1985.[1]

As pyroclastic flows erupted from the volcano’s crater, they melted the mountain’s glaciers, sending four enormous lahars (volcanically induced mudslides, landslides, and debris flows) down its slopes at 50 kilometers per hour (30 miles per hour). The lahars picked up speed in gullies and coursed into the six major rivers at the base of the volcano; they engulfed the town of Armero, killing more than 20,000 of its almost 29,000 inhabitants.[2] Casualties in other towns, particularly Chinchiná, brought the overall death toll to 23,000. […] The relief efforts were hindered by the composition of the mud, which made it nearly impossible to move through without becoming stuck. By the time relief workers reached Armero twelve hours after the eruption, many of the victims with serious injuries were dead. The relief workers were horrified by the landscape of fallen trees, disfigured human bodies, and piles of debris from entire houses. […] The event was a foreseeable catastrophe exacerbated by the populace’s unawareness of the volcano’s destructive history; geologists and other experts had warned authorities and media outlets about the danger over the weeks and days leading up to the eruption.”

“The day of the eruption, black ash columns erupted from the volcano at approximately 3:00 pm local time. The local Civil Defense director was promptly alerted to the situation. He contacted INGEOMINAS, which ruled that the area should be evacuated; he was then told to contact the Civil Defense directors in Bogotá and Tolima. Between 5:00 and 7:00 pm, the ash stopped falling, and local officials instructed people to “stay calm” and go inside. Around 5:00 pm an emergency committee meeting was called, and when it ended at 7:00 pm, several members contacted the regional Red Cross over the intended evacuation efforts at Armero, Mariquita, and Honda. The Ibagué Red Cross contacted Armero’s officials and ordered an evacuation, which was not carried out because of electrical problems caused by a storm. The storm’s heavy rain and constant thunder may have overpowered the noise of the volcano, and with no systematic warning efforts, the residents of Armero were completely unaware of the continuing activity at Ruiz. At 9:45 pm, after the volcano had erupted, Civil Defense officials from Ibagué and Murillo tried to warn Armero’s officials, but could not make contact. Later they overheard conversations between individual officials of Armero and others; famously, a few heard the Mayor of Armero speaking on a ham radio, saying “that he did not think there was much danger”, when he was overtaken by the lahar.[20]

“The lahars, formed of water, ice, pumice, and other rocks,[25] incorporated clay from eroding soil as they traveled down the volcano’s flanks.[26] They ran down the volcano’s sides at an average speed of 60 kilometers (40 mi) per hour, dislodging rock and destroying vegetation. After descending thousands of meters down the side of the volcano, the lahars followed the six river valleys leading from the volcano, where they grew to almost four times their original volume. In the Gualí River, a lahar reached a maximum width of 50 meters (160 ft).[25]

Survivors in Armero described the night as “quiet”. Volcanic ash had been falling throughout the day, but residents were informed it was nothing to worry about. Later in the afternoon, ash began falling again after a long period of quiet. Local radio stations reported that residents should remain calm and ignore the material. One survivor reported going to the fire department to be informed that the ash was “nothing”.[27] […] At 11:30 pm, the first lahar hit, followed shortly by the others.[28] One of the lahars virtually erased Armero; three-quarters of its 28,700 inhabitants were killed.[25] Proceeding in three major waves, this lahar was 30 meters (100 ft) deep, moved at 12 meters per second (39 ft/s), and lasted ten to twenty minutes. Traveling at about 6 meters (20 ft) per second, the second lahar lasted thirty minutes and was followed by smaller pulses. A third major pulse brought the lahar’s duration to roughly two hours; by that point, 85 percent of Armero was enveloped in mud. Survivors described people holding on to debris from their homes in attempts to stay above the mud. Buildings collapsed, crushing people and raining down debris. The front of the lahar contained boulders and cobbles which would have crushed anyone in their path, while the slower parts were dotted by fine, sharp stones which caused lacerations. Mud moved into open wounds and other open body parts – the eyes, ears, and mouth – and placed pressure capable of inducing traumatic asphyxia in one or two minutes upon people buried in it.”

“The volcano continues to pose a serious threat to nearby towns and villages. Of the threats, the one with the most potential for danger is that of small-volume eruptions, which can destabilize glaciers and trigger lahars.[51] Although much of the volcano’s glacier mass has retreated, a significant volume of ice still sits atop Nevado del Ruiz and other volcanoes in the Ruiz–Tolima massif. Melting just 10 percent of the ice would produce lahars with a volume of up to 200 million cubic meters – similar to the lahar that destroyed Armero in 1985. In just hours, these lahars can travel up to 100 km along river valleys.[33] Estimates show that up to 500,000 people living in the Combeima, Chinchina, Coello-Toche, and Guali valleys are at risk, with 100,000 individuals being considered to be at high risk.”

iii. Asteroid belt (featured).

“The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt is also termed the main asteroid belt or main belt to distinguish its members from other asteroids in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, and Hygiea. Vesta, Pallas, and Hygiea have mean diameters of more than 400 km, whereas Ceres, the asteroid belt’s only dwarf planet, is about 950 km in diameter.[1][2][3][4] The remaining bodies range down to the size of a dust particle.”

“The asteroid belt formed from the primordial solar nebula as a group of planetesimals, the smaller precursors of the planets, which in turn formed protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals and most of the protoplanets shattered. As a result, 99.9% of the asteroid belt’s original mass was lost in the first 100 million years of the Solar System’s history.[5]

“In an anonymous footnote to his 1766 translation of Charles Bonnet‘s Contemplation de la Nature,[8] the astronomer Johann Daniel Titius of Wittenberg[9][10] noted an apparent pattern in the layout of the planets. If one began a numerical sequence at 0, then included 3, 6, 12, 24, 48, etc., doubling each time, and added four to each number and divided by 10, this produced a remarkably close approximation to the radii of the orbits of the known planets as measured in astronomical units. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the time (Mercury, Venus, Earth, Mars, Jupiter and Saturn) provided one allowed for a “gap” between the orbits of Mars and Jupiter. […] On January 1, 1801, Giuseppe Piazzi, Chair of Astronomy at the University of Palermo, Sicily, found a tiny moving object in an orbit with exactly the radius predicted by the Titius–Bode law. He dubbed it Ceres, after the Roman goddess of the harvest and patron of Sicily. Piazzi initially believed it a comet, but its lack of a coma suggested it was a planet.[12] Fifteen months later, Heinrich Wilhelm Olbers discovered a second object in the same region, Pallas. Unlike the other known planets, the objects remained points of light even under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from stars. Accordingly, in 1802 William Herschel suggested they be placed into a separate category, named asteroids, after the Greek asteroeides, meaning “star-like”. […] The discovery of Neptune in 1846 led to the discrediting of the Titius–Bode law in the eyes of scientists, because its orbit was nowhere near the predicted position. […] One hundred asteroids had been located by mid-1868, and in 1891 the introduction of astrophotography by Max Wolf accelerated the rate of discovery still further.[22] A total of 1,000 asteroids had been found by 1921,[23] 10,000 by 1981,[24] and 100,000 by 2000.[25] Modern asteroid survey systems now use automated means to locate new minor planets in ever-increasing quantities.”

“In 1802, shortly after discovering Pallas, Heinrich Olbers suggested to William Herschel that Ceres and Pallas were fragments of a much larger planet that once occupied the Mars–Jupiter region, this planet having suffered an internal explosion or a cometary impact many million years before.[26] Over time, however, this hypothesis has fallen from favor. […] Today, most scientists accept that, rather than fragmenting from a progenitor planet, the asteroids never formed a planet at all. […] The asteroids are not samples of the primordial Solar System. They have undergone considerable evolution since their formation, including internal heating (in the first few tens of millions of years), surface melting from impacts, space weathering from radiation, and bombardment by micrometeorites.[34] […] collisions between asteroids occur frequently (on astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years.[63] A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family). Conversely, collisions that occur at low relative speeds may also join two asteroids. After more than 4 billion years of such processes, the members of the asteroid belt now bear little resemblance to the original population. […] The current asteroid belt is believed to contain only a small fraction of the mass of the primordial belt. Computer simulations suggest that the original asteroid belt may have contained mass equivalent to the Earth.[37] Primarily because of gravitational perturbations, most of the material was ejected from the belt within about a million years of formation, leaving behind less than 0.1% of the original mass.[29] Since their formation, the size distribution of the asteroid belt has remained relatively stable: there has been no significant increase or decrease in the typical dimensions of the main-belt asteroids.[38]

“Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that it would be improbable to reach an asteroid without aiming carefully. Nonetheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more, depending on the lower size cutoff. Over 200 asteroids are known to be larger than 100 km,[44] and a survey in the infrared wavelengths has shown that the asteroid belt has 0.7–1.7 million asteroids with a diameter of 1 km or more. […] The total mass of the asteroid belt is estimated to be 2.8×1021 to 3.2×1021 kilograms, which is just 4% of the mass of the Moon.[2] […] Several otherwise unremarkable bodies in the outer belt show cometary activity. Because their orbits cannot be explained through capture of classical comets, it is thought that many of the outer asteroids may be icy, with the ice occasionally exposed to sublimation through small impacts. Main-belt comets may have been a major source of the Earth’s oceans, because the deuterium–hydrogen ratio is too low for classical comets to have been the principal source.[56] […] Of the 50,000 meteorites found on Earth to date, 99.8 percent are believed to have originated in the asteroid belt.[67]

iv. Series (mathematics). This article has a lot of stuff, including lots of links to other stuff.

v. Occupation of Japan. Interesting article, I haven’t really read very much about this before. Some quotes:

“At the head of the Occupation administration was General MacArthur who was technically supposed to defer to an advisory council set up by the Allied powers, but in practice did everything himself. As a result, this period was one of significant American influence […] MacArthur’s first priority was to set up a food distribution network; following the collapse of the ruling government and the wholesale destruction of most major cities, virtually everyone was starving. Even with these measures, millions of people were still on the brink of starvation for several years after the surrender.”

“By the end of 1945, more than 350,000 U.S. personnel were stationed throughout Japan. By the beginning of 1946, replacement troops began to arrive in the country in large numbers and were assigned to MacArthur’s Eighth Army, headquartered in Tokyo’s Dai-Ichi building. Of the main Japanese islands, Kyūshū was occupied by the 24th Infantry Division, with some responsibility for Shikoku. Honshū was occupied by the First Cavalry Division. Hokkaido was occupied by the 11th Airborne Division.

By June 1950, all these army units had suffered extensive troop reductions and their combat effectiveness was seriously weakened. When North Korea invaded South Korea (see Korean War), elements of the 24th Division were flown into South Korea to try to stem the massive invasion force there, but the green occupation troops, while acquitting themselves well when suddenly thrown into combat almost overnight, suffered heavy casualties and were forced into retreat until other Japan occupation troops could be sent to assist.”

“During the Occupation, GHQ/SCAP mostly abolished many of the financial coalitions known as the Zaibatsu, which had previously monopolized industry.[20] […] A major land reform was also conducted […] Between 1947 and 1949, approximately 5,800,000 acres (23,000 km2) of land (approximately 38% of Japan’s cultivated land) were purchased from the landlords under the government’s reform program and resold at extremely low prices (after inflation) to the farmers who worked them. By 1950, three million peasants had acquired land, dismantling a power structure that the landlords had long dominated.[22]

“There are allegations that during the three months in 1945 when Okinawa was gradually occupied there were rapes committed by U.S. troops. According to some accounts, US troops committed thousands of rapes during the campaign.[36][37]

Many Japanese civilians in the Japanese mainland feared that the Allied occupation troops were likely to rape Japanese women. The Japanese authorities set up a large system of prostitution facilities (RAA) in order to protect the population. […] However, there was a resulting large rise in venereal disease among the soldiers, which led MacArthur to close down the prostitution in early 1946.[39] The incidence of rape increased after the closure of the brothels, possibly eight-fold; […] “According to one calculation the number of rapes and assaults on Japanese women amounted to around 40 daily while the RAA was in operation, and then rose to an average of 330 a day after it was terminated in early 1946.”[40] Michael S. Molasky states that while rape and other violent crime was widespread in naval ports like Yokosuka and Yokohama during the first few weeks of occupation, according to Japanese police reports and journalistic studies, the number of incidents declined shortly after and were not common on mainland Japan throughout the rest of occupation.[41] Two weeks into the occupation, the Occupation administration began censoring all media. This included any mention of rape or other sensitive social issues.”

“Post-war Japan was chaotic. The air raids on Japan’s urban centers left millions displaced and food shortages, created by bad harvests and the demands of the war, worsened when the seizure of food from Korea, Taiwan, and China ceased.[58] Repatriation of Japanese living in other parts of Asia only aggravated the problems in Japan as these displaced people put more strain on already scarce resources. Over 5.1 million Japanese returned to Japan in the fifteen months following October 1, 1945.[59] Alcohol and drug abuse became major problems. Deep exhaustion, declining morale and despair were so widespread that it was termed the “kyodatsu condition” (虚脱状態 kyodatsujoutai?, lit. “state of lethargy”).[60] Inflation was rampant and many people turned to the black market for even the most basic goods. These black markets in turn were often places of turf wars between rival gangs, like the Shibuya incident in 1946.”

August 16, 2014 Posted by | Astronomy, Biology, Ecology, Evolutionary biology, Geology, History, Mathematics, Wikipedia, Zoology | Leave a comment

The Emergence of Animals: The Cambrian Breakthrough (II)

I decided to write one more post (this one) about the book and leave it at that. Go here for my first post about the book, which has some general remarks about the book, as well as a lot of relevant links to articles from wikipedia which cover topics also covered in the book. Below I have added some observations from the second half of the book.

“Use of bedrock geology to reconstruct ancient continental positions relies on the idea that if two separated continents were once joined to form a single, larger continent, then there ought to be distinctive geological terranes (such as mineral belts, mountain chains, bodies of igneous rock of similar age, and other roughly linear to irregularly-shaped large-scale geologic features) that were once contiguous but are now separated. Matching of these features can provide clues to the positions of continents that were once together. […] The main problem with using bedrock geology features to match continental puzzle pieces together is that many of the potentially most useful linear geologic features on the continents (such as volcanic arcs or chains of volcanoes, and continental margin fold belts or parallel mountain chains formed by compression of strata) are parallel to the edge of the continent. Therefore, these features generally run parallel to rift fractures, and are less likely to continue and be recognizable on any continent that was once connected to the continent in question.

Paleomagnetic evidence is an important tool for the determination of ancient continent positions and for the reconstruction of supercontinents. Nearly all rock types, be they sedimentary or igneous, contain minerals that contain the elements iron or titanium. Many of these iron- and titanium-bearing minerals are magnetic. […] The magnetization of a crystal of a magnetic mineral (such as magnetite) is established immediately after the mineral crystallizes from a volcanic melt (lava) but before it cools below the Curie point temperature. Each magnetic mineral has its own specific Curie point. […] As the mineral grain passes through the Curie point, the ambient magnetic field is “frozen” into the crystal and will remain unchanged until the crystal is destroyed by weathering or once again heated above the Curie point. This “locking in” of the magnetic signal in igneous rock crystals is the crucial event for paleomagnetism, for it indicates the direction of magnetic north at the time the crystal cooled (sometime in the distant geologic past for most igneous rocks). The ancient latitudinal position of the rock (and the continent of which it is a part) can be determined by measuring the direction of the crystal’s magnetization. For ancient rocks, this direction can be quite different from the direction of present day magnetic north. […] Paleomagnetic reconstruction is a form of geological analysis that is, unfortunately, fraught with uncertainties. The original magnetization is easily altered by weathering and metamorphism, and can confuse or obliterate the original magnetic signal. An inherent limitation of paleomagnetic reconstruction of ancient continental positions is that the magnetic remanence only gives information concerning the rocks’ latitudinal position, and gives no clue as to the original longitudinal position of the rocks in question. For example, southern Mexico and central India, although nearly half a world apart, are both at about 20 degrees North latitude, and, therefore, lavas cooling in either country would have essentially the same primary magnetic remanence. One of the few ways to get information about the ancient longitudinal positions of continents is to use comparison of life forms on different continents. The study of ancient distributions of organisms is called paleobiogeography.”

“Photosynthesis is generally considered to be a characteristic of plants in the traditional usage of the term “plant.” Nonbiologists are sometimes surprised to learn that [some] animals are photosynthetic […] One might argue that marine animals with zooxanthellae (symbiotic protists) are not truly photosynthetic because it is the protists that do the photosynthesis, not the animal. The protists just happen to be inside the animal. We would argue that this is not an important consideration, since photosynthesis in all eukaryotic (nucleated) cells is accomplished by chloroplasts, tiny organelles that are the cell’s photosynthesis factories. Chloroplasts are now thought by many biologists to have arisen by a symbiosis event in which a small, photosynthetic moneran took up symbiotic residence within a larger microbe […]. The symbiotic relationship eventually became so well established that it became an obligatory relationship for both the host microbe and the smaller symbiont moneran. Reproductive provisions were made to pass the genetic material of the symbiont, as well as the host, on to succeeding generations. It would sound strange to describe an oak as a “multicellular alga invaded by photosynthetic moneran symbionts,” but that is — in essence — what a tree is. Animals with photosynthetic protists in their bodies are able to create food internally, in the same way that an oak tree can, so we feel that these animals can be correctly called photosynthetic. […] Many of the most primitive types of living metazoa contain photosymbiotic
microbes or chloroplasts derived from microbes.”

“The most obvious reason for any organism, regardless of what kingdom it belongs to, to evolve a leaf-shaped body is to maximize its surface area. Leaf shape evolves in response to factors in addition to surface area requirement, but the surface area requirement, in all cases we are aware of, is the most important factor. […] Leaves of modern plants and Ediacaran animals probably evolved similar shapes for the same reason, namely, maximization of surface area. […] Photosymbiosis is not the only possible departure from heterotrophic feeding, the usual method of food acquisition for modern animals. Seilacher (1984) notes that flat bodies are good for absorption of simple compounds such as hydrogen sulfide, needed for one type of chemosymbiosis. In chemosymbiosis as in photosymbiosis, microbes (in this case bacteria) are held within an animal’s tissues as paying guests. The bacteria are able to use the energy stored in hydrogen sulphide molecules that diffuse into the host animal’s tissues. The bacteria use the hydrogen sulfide to create food, using biochemical reactions that would be impossible for animals to do by themselves. The bacteria use some of the food for themselves, but great excesses are produced and passed on to the host animal’s tissues. […] There may be important similarities between the ecologies of
[…] flattened Ediacaran creatures and the modern deep sea vent faunas. […] A form of chemotrophy (feeding on chemicals) that does not involve symbiosis is simple absorption of nutrients dissolved in sea water. Although this might not seem a particularly efficient way of obtaining food, there are tremendous amounts of “unclaimed” organic material dissolved in sea water. Monerans allow these nutrients to diffuse into their cells, a fact well known to microbiologists. Less well known is the fact that larger organisms can feed in this way also. Benthic foraminifera up to 38 millimeters long from McMurdo Sound, Antarctica, take up dissolved organic matter largely as a function of the surface area of their branched bodies”

“Although there is as of yet no unequivocal proof, it seems reasonable to infer from their shapes that members of the Ediacaran fauna used photosymbiosis, chemosymbiosis, and direct nutrient absorption to satisfy their food needs. Since these methods do not involve killing, eating, and digesting other living things, we will refer to them as “soft path” feeding strategies. Heterotrophic organisms use “hard path” feeding strategies because they need to use up the bodies of other organisms for energy. The higher in the food pyramid, the “harder” the feeding strategy, on up to the keystone predator (top carnivore) at the top of any particular ecosystem’s trophic pyramid. It is important to note that the term “hard,” as used here, does not necessarily imply that autotrophic organisms have any easier a time obtaining their food than do heterotrophic organisms. Green plants are not very efficient at converting sunlight to food; sunlight can be thought of as an elusive prey because it is not a concentrated energy source […]. Low food concentrations are a major difficulty encountered by organisms employing soft path feeding strategies. Deposit feeding is intermediate between hard and soft paths. […] Filter feeding, or capturing food suspended in the water, also has components of both hard and soft paths because suspension feeders can take both living and nonliving food from the water.”

“Probing deposit feeders […] began to excavate sediments to depths of several centimeters at the beginning of the Cambrian. Dwelling burrows several centimeters in length, such as Skolithos, first appeared in the Cambrian, and provided protection for filter-feeding animals. If a skeleton is broadly defined as a rigid body support, a burrow is in essence a skeleton formed of sediment […] Movement of metazoans into the substrate had profound implications for sea floor marine ecology. One aspect of the environment that controls the number and types of organisms living in the environment is called its dimensionality […]. Two-dimensional (or Dimension 2) environments tend to be flat, whereas three-dimensional environments (Dimension 3) have, to a greater or lesser degree, a third dimension. This third dimension can be either in an upward or a downward direction, or a combination of both directions. The Vendian sea floor was essentially a two-dimensional environment. […] With the probable exception of some of the stalked frond fossils, most Vendian soft-bodied forms hugged the sea floor. Deep burrowers added a third dimension to the benthos (sea floor communities), creating a three-dimensional environment where a two-dimensional situation had prevailed. The greater the dimensionality in any given environment, the longer the food chain and the taller the trophic pyramid can be […]. If the appearance of abundant predators is any indication, lengthening of the food chain seems to be an important aspect of the Cambrian explosion. Changes in animal anatomy and intelligence can be linked to this lengthening of the food chain. Most Cambrian animals are three-dimensional creatures, not flattened like many of their Vendian predecessors. Animals like mollusks and worms, even if they lack mineralized skeletons, are able to rigidify their bodies with the use of a water-filled internal skeleton called a coelom […] This fluid-filled cavity gives an animal’s body stiffness, and acts much like a turgid, internal, water balloon. A coelom allows animals to burrow in sediment in ways that a flattened animal (such as, for instance, a flatworm) cannot. It is most likely that a coelom first evolved in those Vendian shallow scribble-trail makers that were contemporaries of the large soft-bodied fossils. Some of these Ediacaran burrows show evidence of peristaltic burrowing. Inefficient peristaltic burrowing can be done without a coelom, but with a coelom it becomes dramatically more effective.”

Bilateral symmetry is important when considering the behavior of […] early coelomate animals. The most likely animal to evolve a brain is one with bilateral symmetry. Concomitant with the emergence of animals during the Vendian was the origin of brains. The Cambrian explosion was the first cerebralization or encephalization event. As part of the increase in the length of the food chain discussed above, higher-level consumers such as top or keystone predators established a mode of life that requires the seeking out and attacking of prey. These activities are greatly aided by having a brain able to organize and control complex behavior. […] Specialized light receptors seem to be a characteristic of all animals and many other types of organisms; […] photoreceptors have originated independently in at least forty and perhaps as many as sixty groups. Most animal phyla have at a minimum several pigmented eye spots. But advanced vision (i. e., compound or image-forming eyes) tied directly into a centralized brain is not common or well developed until the Cambrian. The tendency to have eyes is more pronounced for bilateral than for radial animals. […] some of the earliest trilobites had large compound eyes. Trilobites were probably not particularly smart by modern standards, but chances are that their behavioral capabilities far outstripped any that had existed during the early Vendian. […] Actively moving or vagile predators are, as a rule, smarter than their prey, because of the more rigorous requirements of information processing in a predatory life mode. Anomalocaris as a seek-and-destroy top predator may have been the brainiest Early Cambrian animal.”

“why didn’t brains and advanced predation develop much earlier that they did? A simple, thought experiment may help address this problem. Consider a jellyfish 1 mm in length and a cylindrical worm 1 mm in length. Increase the size (linear dimension) of each (by growth of the individual or by evolutionary change over thousands of generations) one hundred times. […] The worm will need internal plumbing because of its cylindrical body. The jellyfish won’t be as dependent on plumbing because its body has a higher surface area. […] Our enlarged, 10 cm long worm will possess a brain which has a volume one million times greater than the brain of its 1 mm predecessor (assuming that the shape of the brain remains constant). The jellyfish will also get more nerve tissue as it enlarges. But its nervous system is spread out in a netlike fashion; at most, its nerve tissue will be concentrated at a few radially symmetric points. The potential for complex and easily reprogrammed behavior, as well as sophisticated processing of sensory input data, is much greater in the animal with the million times larger brain (containing at least a million times as many brain cells as its tiny predecessor). Complex neural pathways are more likely to form in the larger brain. This implies no mysterious tendency for animals to grow larger brains; perfectly successful, advanced animals (echinoderms) and even slow-moving predators (sea spiders) get along fine without much brain. But centralized nerve tissue can process information better than a nerve net and control more complex responses to stimuli. Once brains were used to locate food, the world would never again be the same. This can be thought of as a “brain revolution” that permanently changed the world a half billion years ago.”

“There is little doubt that organisms produced oxygen before 2 billion years ago, but this oxygen was unable to accumulate as a gas because iron dissolved in seawater combined with the oxygen to form rust (iron oxide), a precipitate that sank, chemically inactive, to accumulate on the sea floor. Just as salt has accumulated in the oceans over billions of years, unoxidized (or reduced) iron was abundant in the seas before 2 billion years ago, and was available to “neutralize” the waste oxygen. Thus, dissolved iron performed an important oxygen disposal service; oxygen is a deadly toxin to organisms that do not have special enzymes to limit its reactivity. Once the reduced iron was removed from sea water (and precipitated on the sea floor as Precambrian iron formations; much of the iron mined for our automobiles is derived from these formations), oxygen began to accumulate in water and air. Life in the seas was either restricted to environments where oxygen remained rare, or was forced to develop enzymes […] capable of detoxifying oxygen. Oxygen could also be used by heterotrophic organisms to “burn” the biologic fuel captured in the form of the bodies of their prey. […] Much research has focused on lowered levels of atmospheric oxygen during the Precambrian. The other alternative, that oxygen levels were higher at times during the Precambrian than at present has not been much discussed. Once the “sinks” for free oxygen, such as dissolved iron, were saturated, there is little that would have prevented oxygen levels in the Precambrian from getting much higher than they are today. This is particularly so since there is no evidence for the presence of Precambrian land plants which could have acted as a negative feedback for continued increases in oxygen levels” [Here’s a recent-ish paper on the topicdo note that there’s an important distinction to be made between atmospheric oxygen levels and the oxygen levels of the oceans].

August 4, 2014 Posted by | Biology, Books, Botany, Ecology, Evolutionary biology, Geology, Microbiology, Paleontology, Zoology | Leave a comment

The Emergence of Animals: The Cambrian Breakthrough (I)

Here’s what I wrote about the book on goodreads:

This book is almost 25 years old, and this is one of the main reasons why I did not give it five stars. Parts of this book is just amazing, but the fact that I felt that it was necessary to continually look up terms and ideas covered in the book made it slightly less fun to read than it could have been. Some parts of the scientific vocabulary applied throughout the book are frankly outdated, and this aspect reflects not only a change in which words are used but also, more importantly, a change in how people think about these things. That progress has been made since the book was written is a good thing, but it did subtract a little from the overall reading experience that I very often felt that I had to be quite careful about which specific conclusions to accept and which to question. It does not help that some of the main conclusions towards the end of the book seem to have been proven, for lack of a better word, wrong.

But all in all it’s really a very nice book – there’s a lot of fascinating stuff in there.”

A few sample quotes from the book:

“a distinction needs to be made between the two major types of animal fossils — body fossils and trace fossils. Body fossils are either actual parts of the organism’s body (such as a shell or a bone), or impressions of body parts (even if the parts themselves have been dissolved away or otherwise destroyed). The imprint of a feather or leaf or the external surface of a shell are examples of body fossils. […] Trace fossils are markings in the sediment (usually made while the sediment was still soft) left by the feeding, traveling, or burrowing activities of animals. Familiar examples of trace fossils include tracks and trails made by worms as they plow through sediment looking for food and ingesting sediment. […] Completely unrelated organisms can make trace fossils which are indistinguishable to paleontologists. Trace fossils are part of the fabric of the sediment, and therefore can be very resistant to destruction by metamorphism of the surrounding rock. Body fossils, on the other hand, are often destroyed by chemical reactions with the surrounding sediment. But body fossils are the only fossil type that can consistently give reliable information about the identity of the organism which left the remains. […] The worst problem in the search for the oldest animal fossils is mistaken identity. Sedimentary rocks are replete with irregular structures and small scale disturbances or interruptions of the horizontal bedding or layering. Some of these disturbances are caused by organisms, but many are not. […] Usually a well-preserved and well-formed trace fossil is unquestionably biologic in origin, and all paleontologists would agree that the trace was formed by an animal. Yet it can be difficult to define precisely what it is about a trace fossil that makes it convincingly biogenic (formed by life). […] A sedimentary structure that resembles, but is in fact not, a trace fossil (or a body fossil, for that matter) is called a pseudofossil. Pseudofossils have plagued the study of Precambrian paleontology because many inorganic sediment disturbances look deceptively like fossils.”

“Convincing trace fossils are known from the late Precambrian, sometimes in association with the soft bodied Ediacaran fossils (Glaessner 1969). These trace fossils are generally simpler, less common, and less diverse than Cambrian trace fossils. There is a significant difference in the complexity and depth of burrowing between Cambrian and Precambrian trace fossils, and it has been argued that the changeover from simple trace fossils to more complex types of traces occurred at more or less the same time as the Cambrian explosion, the first appearance of abundant Cambrian shelly fossils. […] Even shallow, sediment surface burrows in the Cambrian show a marked change in character over their Precambrian predecessors. […] something outstanding happened to the abilities of trace-fossil makers across the Precambrian-Cambrian boundary. Animals discovered a large number of ways to effectively use the sediment as a food resource, and also began to move deeper into the substrate for deposit feeding and homebuilding.”

“Seilacher (1984, 1985) recognizes that flattened body shapes maximize surface area for the takeup of oxygen and food dissolved in seawater, and perhaps also for the absorption of light. “Normal” metazoan animals generally have plump, more or less cylindrical, bodies. For very small, thin skinned animals, cells near the body surface can get oxygen and expel waste by simple diffusion across the cell surface membranes. Waste products such as carbon dioxide will be supersaturated inside of the animal’s body, and will tend to migrate out of its cells and into the open environment. The reverse is true for oxygen; it will tend to migrate into the cells because its concentration is greater on the outside than on the inside of an oxygen-respiring animal. Animals such as frogs and salamanders are able to respire (at least in part) in this way. But for most large, cylindrical animals, diffusion respiration will not work because diffusion is ineffective for cells buried deep within the animal’s body. This is a consequence of the fact that as an animal increases its size, its total volume outstrips its surface area by a large margin. […] metazoans have developed intricate systems of pipework and tubing to deliver nutrient and waste removal services to interior cells. Circulatory systems, digestive tracts, gills, and lungs are all solutions to the problems associated with volume increase.”

Monoplacophorans […] are cap-shaped shells distinguished by two rows of muscle scars on the interior of the shell. They were thought extinct until living specimens were dredged from the deep sea and described in the late 1950s. Monoplacophorans have had an unusual history of discovery. They are the only group of animals that has been: (a) described hypothetically before being discovered; (b) found as fossils before being found alive,- and (c) dredged from the depths of the oceans before being collected from shallower marine waters (Pojeta et al. 1987). […] Rostroconchs are a major, extinct, order of mollusks that first appeared in the earliest Cambrian. Rostroconchs have a shell that is shaped like a clam shell, except that instead of having an organic ligament connecting the two valves, the two halves of a rostroconch shell are fused together to form a single valve. Despite this fusion, larger rostroconchs look very much like clam fossils with valves still articulated, which partly explains why rostroconchs were not recognized as a major, distinct, group until the 1970s. […] Slightly after the first appearance of rostroconchs, the first true clams or bivalves appear. Clams probably had the same ancestor as the rostroconchs […]. Instead of keeping the two valves fused as in rostroconchs, clams hinged the valves with articulating teeth and a tough, organic ligament. This evidently proved to be the more successful approach, since bivalve shells now litter the beaches all over the earth, whereas rostroconchs dwindled to extinction in the Permian.”

“Of the earliest Cambrian shelly fossils, many groups are truly problematic in the sense that not only do we have no idea what kind of animal made them, but also we have no clear conception of the function or functions of the skeletal remains. […] there is an anomalously high proportion of small shelly fossils that do not belong to later phyla. “Living fossils” are creatures alive today that have undergone very little morphologic change for long stretches (sometimes 100 million years or more) of geologic time. Few living fossils remain from the earliest Paleozoic fauna. […] Many of the groups that were most important in the Cambrian are unimportant or extinct today, for example, the trilobites, the inarticulate brachiopods, hyoliths, monoplacophorans, eocrinoids, the sclerite-bearers, and phosphatic tube-formers. True metazoans were undoubtedly present before the Cambrian, but they were all, with [few] exception[s] […], soft-bodied. New types of soft-bodied animals appear in the Cambrian as well, but our understanding of these forms is restricted to rare finds of Cambrian soft-bodied fossils, which are even rarer than finds of the Ediacaran fauna.”

I’ll just quote that last part again: “our understanding of these forms is restricted to rare finds of Cambrian soft-bodied fossils”.

They’re talking about the findings of soft-bodied organisms who did not make shells or anything like that which lived more than 500 million years ago. To get a sense of perspective in terms of how long ago this is, have a look at this picture – that’s one guess at what we think the Earth might have looked like back then. In my mind, the fact that we know anything at all about soft-bodied animals living back then is pretty amazing to think about.

I could easily write perhaps four posts about this book, but I’m not going to do that. Instead I have decided for now to limit my coverage here to the stuff above and some links to relevant stuff I looked up while reading the book, which I have posted below – I was surprised how much relevant stuff wikipedia has on related matters, and if you’re curious you should really go have a look at some of those links. I should note that I will probably add another post about the book later on with some more observations from the book – it seems wrong to me to limit coverage of this great book to one post, but there’s no way I can cover all the good stuff in there anyway.

Here are as mentioned some relevant wiki links to the kinds of stuff they talk about in this book – most of the links are in my opinion links to articles of what I’d consider to be a ‘reasonable’ length/quality, and although I have not read all of them I’d note that some of them are quite good:

Cambrian explosion.
Ediacara biota (featured).
Kleptoplasty.
Trace fossil.
Cloudinid (‘good article’).
Sclerite.
Archaeocyatha.
Trilobite.
Echinoderm.
Brachiopod (‘good article’).
Bivalvia (featured).
Chiton.
Bryozoa (‘good article’).
Adam Sedgwick.
Roderick Murchison.
Global Boundary Stratotype Section and Point (noteworthy in this context is that the Precambrian/Cambrian boundary GSSP at Fortune Head had not been decided upon when this book was written – they have a whole chapter about these and related things).
Manorian glaciation (this is not what it’s called in the book, but that is what they’re talking about anyway).
Snowball Earth.
Timeline of glaciation.
Cryogenian.
Rodinia.
Mirovia.
Curie temperature.
Autotroph.
Heterotroph.
Microbial mat.
Anomalocaris.
Stromatolite.
Acritarch.
Great Oxygenation Event.
Methane clathrate.

July 29, 2014 Posted by | Biology, Books, Ecology, Evolutionary biology, Geology, Paleontology, Zoology | Leave a comment

Geomorphological Landscapes of the World (2)

I decided to write another post about this book (first post here). I’m almost finished with Metabolic Risk for Cardiovascular disease which I’ve been reading over the last few days, but I figure coverage of that one can wait a little (it’s not that great).

I have tried to pick out passages in the coverage below which should not be too hard for the ‘uninitiated’ to understand, and I hope that I have been successful. I’ve added links here and there to help making the post easier to read. I don’t really have a lot of new stuff to say about book, so I’ll get right to it.

Badlands occur worldwide and are especially common in the Northern Great Plains of North America. […] Badlands worldwide are formed by the forces of gravity and running water, especially by the process of slopewash erosion, which reaches its maximum potential under the combination of: (1) steep local topography; (2) weakly cemented, poorly indurated, readily eroded bedrock; and (3) a semiarid continental climate that supports a sparse vegetation cover, yet delivers precipitation in relatively high-magnitude, short-lived convective storms. This combination ensures that hillslopes are highly vulnerable to erosion, and erosive forces of running water reach their maximum expression on Earth. […]

Erosion has been the primary landscape-forming process [in the Great Plains badlands] over the past 5 million years during PlioPleistocene time (Bluemle 2000). Naturally, this erosion was not uniform. Well-indurated, freshwater limestone (lake) deposits and coarse-caliber, gravel (stream) deposits served as resistant caprocks on lowlying parts of the Miocene landscape. As the overall landscape was eroded, these former low spots (lakes and rivers) were more resistant to erosion and became isolated as topographic high spots – modern-day buttes and mesas […] This process of creating high topographic points from formerly low points is known as topographic inversion.”

“Conceptually, the formation of Grand Canyon should be very simple to explain. The Colorado River floods annually in the spring from snowmelt in the Rocky Mountains. These floods exert large tractive (erosional) forces against the bed of the river. Over many millions of years the river cut the magnificent canyon into the adjacent plateaus. In actuality, the processes are far more complicated and have not been completely explained.”

“The evolution of the quartzite landscape of the Gran Sabana has been a very long-term process. The rocks are very ancient, the region geologically stable, and the highest planation surfaces, forming the tepui summits and the plains of the surrounding Gran Sabana have been exposed for more than 70 million years, probably since the mid-Mezozoic (Jurassic?) […] It is this aspect of very, very, long periods of time for weathering, longer than most places on Earth, which is probably critical for the development of the striking landscapes of the Gran Sabana.” (Below a picture of what it looks like, from the wiki:)

800px-Kukenan_Tepuy_at_Sunset
(I should note that that wiki article was, as far as I know, the first article I’ve come across that had multiple featured images.)

“The Iguazu Falls are one of the most beautiful in the world because of the combination of a high and wide structural step across a fluvial system with large water discharge and the tropical environmental location that sustains an exuberant forest and high biodiversity. The geology of the area consists of three layers of basalts that give a staircase-type shape to the falls. The Iguazu River is about 1,500 m wide above the falls and forms many rapids between rock outcrops and small islands. The falls have a sinuous arch-like head 2.7 km long, and part of water volume enters a canyon 80–90 m wide and 70–80 m deep, forming the spectacular “Garganta do Diabo” (Devil’s Gorge). Part of river water enters the canyon by its left side and generates a front with 160–200 individual falls that form a unique wall of water during floods. Although no absolute ages exist on the evolution of the fluvial system, it has been suggested that the falls have been continuously wandering upstream to its present position by progressive headwater erosion at a rate of 1.4–2.1 cm/year in the last 1.5–2.0 million years.”

391px-Iguacu-004(Picture from wikipedia)

“South America is drained by huge and complex drainage systems, especially in tropical areas, and […] the largest South American rivers contribute to 28% of the total fresh water to the oceans […] The Paraná River basin started to develop concurrently with the rifting processes, related to the opening of the South Atlantic, when Gondwanaland was dismembered. River valley formation surely started after the prevailing desert conditions during part of the Cretaceous age, when a big sand sea spread along a large part of southeastern Brazil (Caiua Group). During this time the development of endorreic drainage under arid to semi-arid conditions could be the first evidence of a fluvial system being present in the former Paraná Basin after the immense basaltic extrusion event linked to the Gondwana partition. Despite its long history, the Paraná fluvial system is not well-understood […] there are strong controversies about the age of the present Paraná River system.”

“The Dry Valleys comprise an ice-free part of the Transantarctic Mountains in Antarctica, bounded by the East Antarctic Ice Sheet on the landward side and a coastal ice dome at the coast. Weathering rates are among the lowest on Earth and reflect the persistent hyper-arid, cold polar desert climate. Some buried ice has survived for over 8 million years. The main escarpments and valleys were created on a passive continental margin as Antarctica split from Australia some 55 million years ago. […] Geomorphological evidence of weathering rates suggests that the climate of the last 13.6 million years has been stable and remained dry and cold throughout. The important implication is that the ice sheet that controls the climate has also been present throughout. […] Intriguingly, the climate and processes of the higher parts of the Dry Valleys overlap with conditions on Mars.”

“If there is a single landform that might typify the landscape of Africa, then this would be an isolated bare rock hill or mountain rising from the vast plains. Hills of this sort struck an early German explorer of East Africa, Walter Bornhardt, so much that he invented a special term and called them inselbergs, literally meaning “island hills” […] Inselbergs vary in terms of lithology, dimensions, height, and shape, but have a few characteristics in common. First, as the name implies, they stand in isolation and are surrounded by a flat or gently rolling topography. Second, the topographic boundary between the hillslope and the plain around is fairly abrupt. Third, inselbergs are residual landforms due to wearing down of the surrounding terrain. Hence, volcanic cones and up-faulted blocks are traditionally not regarded as members of the inselberg family. The vast majority of inselbergs is built by strong and resistant rock, and very often this rock is granite […]

Spiztkoppe is one of the tallest, if not the tallest inselberg on Earth. Its summit rises to 1,728 m a.s.l. and overlooks the adjacent plains by 600 m. […] The evolution of the granite landscape of the Spitzkoppe inselbergs has been a complex and long-lasting process. The granite belongs to the family of Early Cretaceous (137–124 Ma ago) intrusions [according to the wiki, ‘The granite is more than 700 million years old’ – having read the chapter about it in this book, I’d say that claim merits a ‘citation needed’] […] The intrusions were emplaced at depths of several km below the ground surface that existed at the time. When the granites of Spitzkoppe were exposed to daylight is not known with precision […] The mean denudation rate was high in the late Cretaceous/early Tertiary, and perhaps several kilometers of rock were lost, but then surface lowering proceeded at a lower rate, decreasing further since the Miocene. Cosmogenic isotope dating suggests that the mean denudation rate in the last 10 million years has been of the order of 5 m/1 million years. Hence, by simple extrapolation and assuming (unrealistically!) no denudation at the site of the future inselberg, 120 million years would be required to produce a 600 m high residual hill. Allowing for an increasing denudation rate prior to 10 million years ago, these rates indicate that the tops of the inselbergs may have been exposed as early as in the late Cretaceous, ~80–70 million years ago. Over time, their height increased as the surrounding terrain built of less resistant rock was worn down. Evidently […] inselbergs have a very long history”

“The Afar Triangle is a barren lowland bounded by the Red Sea and the two blocks of Ethiopian Highlands […] its terrain is a casebook of tectonic geomorphology. Plate divergence is at its most obvious where the Red Sea has opened, and is still opening, between the Arabian and African plates. The African plate is breaking apart along the well-known East African Rifts, separating the Somalian plate from the main continental block (often known as the Nubian plate in the north). These three divergent boundaries have a triple junction at the Afar. The Triangle is the one place where the coastlines and plateau margins cannot be fitted neatly back into their pre-divergent entity – because the locally excessive constructive process of basalt generation has created anew the youthful lowland that is the Afar. […] ‘Hostile environment’ is a term tailor-made for the awful, hot, barren desert of the Afar […] Just one river enters it, and none leaves it. A few salt lakes contain almost the only water not yet lost to solar evaporation. Daily temperatures are 30–40°C in the cool of winter; summer regularly sees shade temperatures of 50°C on the floor of the Danakil Depression – and there is no shade.”

“The largest single feature of the Afar is the Danakil Depression, which descends to 126 m below sea level over the line of current plate divergence, and would be larger except that half its floor is occupied by shield volcanoes. […] Of the 34 volcanoes listed within the Afar Triangle, five have recorded activity within historical time. The largest and most frequently eruptive is Erta Ale, rising from the floor of the Ethiopian sector of the Danakil Depression. It is a classic shield volcano […] Its perimeter is more than 100 m below sea level within the depression, and its summit rises to 613 m above sea level […] Erta Ale is unique in that it has contained lava lakes that, between them, have been persistently active for at least 100 years […] The currently active lake lies within the central vent, which is a spectacular pit crater, developed by collapse when magma pressure declined beneath it. Only 60 m across when first recorded in 1968, it is now 150 m across, and about 80 m deep. A lava lake normally covers all or part of its floor, and has periodically overflowed. The lava has a temperature of about 1,200°C, while the rafts of chilled crust that cover most of its lake surface are at about 500°C. […] The continuing survival of Erta Ale’s lava lake relies on a substantial heat supply to match its thermal loss into the atmosphere […] This heat supply is from rising magma that is feeding a zone of active emplacement of dykes and sills. Within the immediate vicinity of the volcano, these intrusions currently fill new fissures to keep pace with the plate divergence, so that they largely prevent further fault-related subsidence in the Erta Ale sector of the main graben.”

February 15, 2014 Posted by | Books, Geology | Leave a comment

Geomorphological Landscapes of the World

I finished the book today – I liked it and gave it 3 stars on goodreads.

The Earth has a lot of interesting and beautiful places. Having a closer look at some of these wonderful places and trying to understand in some detail how those places came to be, how they formed and evolved, what they’re made of, etc. is what this book is all about. From the Mackenzie Delta in Canada over various awesome parts of the US, on to the Cockpit Country of Jamaica and the Southern Patagonian Andes to the McMurdo Dry Valleys of Antarctica, crossing Africa while talking about among other things the Namib Sand Sea, Spitzkoppe and the Afar triangle (considering the fact that you have lava lakes(!) here and that this area in general is just crazy – it includes a rift valley half-filled with volcanos… there’s incredibly little material about this place on e.g. wikipedia), having a look at Europe (the Dolomites, Dorset (this article is better than most of the above, I’d say from a brief skim), the Norwegian Fjords, amongst others things), moving on to Asia (Western Ghats, Pokhara Valley, some talk about Fenglin karst, Mt. Fuji, Mulu – among other things) and to Australia (Uluru, Bungle Bungle) and New Zealand. The book was written in order to help you to understand which physical processes have caused beautiful places all over the world to look the way they do today. I think such knowledge makes the beauty of all these places easier to appreciate – it always adds, I don’t understand how it subtracts. As for some of the places it seems obvious to me that you can only truly appreciate the beauty of those places if you also understand some of the underlying processes. It’s a bit like comparing the looks of a potential partner about whom you know nothing with the looks of the same potential partner after he or she has just told you his/her deeply fascinating life story (at least I think this is a good analogy; I’m not sure as I don’t have a lot of experience with these sorts of things).

There’s a snag, though. The book will certainly help you understand some of these things better if you’ve read a geology textbook or two before you start out – a book like this one. I should point out that one textbook may not be enough – despite having read Press and Siever I was often struggling to make sense of the material, having to look up stuff frequently, but that may be related to the fact that I read that book a while ago and so have forgotten a lot of stuff in the meantime. However if you have no background at all in physical geography and haven’t read anything about this kind of stuff, you’ll get very little out of this book. You’ll probably have a ‘…yes, I understand a few of those words…’-experience instead (and oftentimes the words you’ll understand will not help you understand what the authors are trying to tell you…). Of course you can read the words and look up all the ones you don’t understand, but most normal people are not going to read 350 pages that way if there are a lot of words in the second category. And although there are some (sometimes amazing, breathtaking..!) pictures in there, that’s probably not going to be enough…

“In basic terms, the geology at the western part of the entrance of the Guanabara Bay, including the Sugar Loaf and its vicinity, is represented by Meso- Neoproterozoic high grade metasedimentary rocks intruded by Neoproterozoic syn- to post-tectonic granitoid rocks and thin Cretaceous diabase dikes (Silva and Ramos 2002; Valeriano et al. 2003).”

In basic terms indeed – it would be interesting to see their contributions to a simple-wikipedia article. To be fair, you can say quite a bit more than that and they spend some pages talking about these things. Here’s the abstract to a chapter (all chapters have abstracts in the beginning, like all Springer publications) from the middle of the book, chapter 18 (I picked this abstract because it was in the middle of the book – there are 37 chapters altogether; I don’t think it’s a ‘special’ abstract as such):

“The landform history of the sandstone scarpland, inselberg and plains landscape of the greater Djado region, part of the presently hyper-arid central Sahara, in north-eastern Niger, begins with all-encompassing Paleogene etchplanation under humid-tropical conditions, followed by the almost compete stripping of the original soil cover and silcrete induration of the uniform etchplain during the Oligocene. Still under very humid conditions, deep-reaching karstification then penetrates silcrete, contemporaneous ferricrete and, above all, the saprolitic sandstones, also creating numerous poljes. Gradually decreasing humidity up to the end of the Neogene, resulting in increasingly restricted etchplanation, leads to the formation of scarplands, inselbergs, intra-plateau basins, pediments, and still sandstone-karstrelated scarpfoot depressions. During a final relapse to quite humid conditions, landslide fringes form along all heterolithic escarpments at the onset of the Pleistocene, later on merely subject to fluvial dissection in the context of at least three phases of Quaternary pluvial river aggradation and terrace formation. A thorough reshaping of most of the region under Quaterary arid conditions is effected by more than one phase of aeolian corrasion, as part of the largest wind-corrasion landscape on Earth.”

It makes more sense in context (well, maybe it makes perfect sense to you already – if so you’ll probably have no problems with the book), but I have actually punished the authors for the technical nature of the publication this time; if you’re a geologist this book is probably a four or five star publication, but some of these guys have made the book really hard to read for people outside the field, and this is part of the reason why I only gave it three stars. It’s a bit too much trouble to read and understand the book, and that’s a damn shame because it’s interesting stuff they cover. Having said this I should add though that I’ll probably try to remember in the future that I have this book, in case I suddenly become very rich and feel a great desire to travel the world. You’ll want to know stuff like the stuff in this book if you’re ever going to visit those places – if you don’t know this kind of stuff your experience will be partly spoiled (compared to the alternative) on account of your ignorance. And there’s a lot of stuff in this book you’ll not be able to find covered online unless you really know where to look, and are willing to spend some time looking.

The book will tell you about how some waterfalls have ‘travelled’/retreated many kilometres over time because steep slopes and huge amounts of water lead to powerful erosive forces impacting the edges of the waterfalls in particular. It’ll also tell you about how some prominent features in various landscapes are really only prominent because they‘re all that’s left standing – everything else has been eroded away over millions of years. Mountains don’t always rise from the ground in the way that we usually conceptualize it – see also these images (no good wiki article about these, unfortunately). Most people probably think of cinder cone volcanos as majestic structures which have been around for a very long time. Some of them are a bit like this, but even if they are they probably have a complicated history; lava used to come out other places than you’d think, maybe the volcano has migrated over time. They sometimes do this. But then there are other kinds of volcanos. A couple of years before my father was born Parícutin was an unexceptional bit of dirt and ground on a Mexican cornfield. Then something interesting happened. A fissure formed in the ground on the 20th of February 1943 – within the first day the cone that popped up shortly after had grown to a height of 6 metres. On the 23rd of February it was 60 metres high. Half a year later, in October, the cone had reached a height of 300 metres (I should note that the numbers in the wikipedia article are somewhat different, but different numbers are provided by different sources and although the numbers differ a bit they tell a rather similar story – this volcano became very big very fast, and it basically grew out of nothing). Lava flows started running on the 23rd of February, and these ended up covering approximately 25 km2 of the surrounding areas, impacting five nearby villages (as the book notes, other effects had much wider consequences: “Ash-fall impact was much higher: the 1 m isopach covered an area of 61 km2, while the 25 cm isopach had an envelope of 233 km2, and the 1 mm isopach up to 60,000 km2.”). The volcano is no longer active – it was ‘only’ active for roughly 10 years. Nobody died. People living on Iceland were not so lucky when their island was hit by a major eruption roughly 200 years ago; that eruption killed roughly one in five people living on the island.

But talking about these things is perhaps problematic in that a big point is easy to miss; the history of the Earth is long. It’s incredibly long. This book deals with a smallish volcano showing up almost out of thin air within the lifetime of some of the readers, because that’s actually pretty amazing. But there are lots of different types of ‘amazing’ out there. A lot of interesting places have taken a long time to get to where they are now. Geological processes have been going on for a long time. A really long time. Things used to look very different, in ways which are hard to even imagine now. Continents used to be located in very different places from the places they’re located today, and the reasons why they no longer are located where they used to be located may sometimes explain why they look the way they do. Some places which are parts of various continents now used to be at the bottom of the ocean, and this includes some pretty prominent mountain ranges. It’s not perfectly clear in detail when ice became a really big deal in Antarctica, but it’s safe to say that until roughly 35 million years ago it certainly wasn’t anything much to write home about, and that near-complete ice cover didn’t happen until much later. One should also not forget that both Europeans and Americans actually had plenty of the stuff just a few tens of thousands of years ago – remember those Norvegian Fjord’s we were talking about?

The world is an interesting place, and learning more about it usually makes it more interesting. Although many of the things covered in the book are not well covered on wikipedia, I thought I should at least add some links to relevant articles covering related stuff (I bookmarked some of the articles I looked up while reading the book in order to make it easier to cover on the blog; I was questioning quite early on whether it would make sense to quote extensively from the book here), so I’ve done this below:

Karst.
Gran Sabana.
Barchan.
Saltation.
Variscan orogeny.
Coral reef.
Sill.
Diabase.
Doline.
Vadose zone.
Speleology.
Solifluction.
Peneplain.
Mass wasting.
Rock glacier.

I probably haven’t covered this book in the amount of detail it deserves. It’s a good book – and some chapters were really fascinating – it’s just a bit hard to read. If I don’t get a lot of reading done within the next days I may decide to add some more detailed coverage of this book here on the blog.

February 12, 2014 Posted by | Books, Geology | Leave a comment