Looking past old bones

 kw: book reviews, nonfiction, science, geology, paleontology, plants, evolution

Cyanobacteria, which were called "blue-green algae" when I was taking Freshman botany more than sixty years ago, arose about 2.7 billion years ago. The Earth started to become green. Before that it was primarily orange. The greening of Earth began in earnest once certain cyanobacteria became incorporated into the cells of an Archaean species to become chloroplasts in the first eukaryotic cells. Multicellularity, in the sense that among a bunch of cells that were sticking together, the cells began to have different functions, came about perhaps 1.5 billion years ago. By 1.2 billion years ago a proto-alga we call Bangiomorpha was the tallest plant in the shallows of the Precambrian ocean, being all of 2 mm tall, towering over micron-sized prokaryotes.

Bangiomorpha features in the first chapter of When the Earth was Green: Plants, Animals, and Evolution's Greatest Romance by geologist Riley Black. The chapter is titled "Sex in the Shallows" because it is pretty certain that Bangiomorpha was among the first organisms to reproduce via sexual differentiation of gametes and gamete fusion.

Side note, not related to the content of the book: The preference in nature to use DNA rather than RNA for long-term storage and retrieval of genetic information is based on its stability. RNA copying is much more prone to error, and the lack of pairing of RNA strands makes an "RNA world" very fragile. However, RNA is essential for helping DNA make copies of itself, and for translating sections of DNA into proteins. The fact that the biosphere was extremely slow to change during the first billion years after life began indicates that DNA is "too slow"! The mix-and-match processes of meiosis and gametogenesis sped things up appropriately, so that complex life could arise before the Sun burned out (not that "nature" had any idea it had such a deadline). Sex combines a level of stability much greater than an RNA basis allows, while also providing mechanisms for making changes more rapidly, particularly when small populations are isolated under adverse conditions. As you might imagine, biological theorists are still arguing strenuously about the pace of evolutionary change at various levels.

Back to the book: The fifteen chapters each tell a story of a particular organism or ecosystem, focusing on the plants. Most of paleontology is "shells and bones". Having done my time clambering over desert landscapes all over North America—as Riley Black is still doing, lucky kid!—I relate strongly to the tendency to focus on the hard bits. It is easy to climb a cliff that was a marine reef in the Pennsylvanian Era and snatch up brachiopods, bryozoans, clams, snails, and corals. The plants that accompanied them are simply not in evidence; they don't fossilize well in the gritty sands that surround the structures of the reef. And why collect fossils in deserts? I live in Delaware now, and most rocks containing fossils are buried under tens of feet of soil. In Nevada, there are lots of rocks right at the surface.

Some of the chapters tell stories that feature sundry animals, retaining the emphasis on the plants they lived among, and often upon. For example, Chapter 13, "Far from the Tree" has a proto-hyena watching two monkeys squabble on the branch of a tree in late Miocene Ethiopia, hoping one will fall. The tree is the "hero" of the story, along with the effects tree dwelling had on the morphology of the little primates. The focus of the chapter is the gradual spread of grasses as the forests retreat. 

By the way, it is stated that grasses have C3 photosynthesis, making them more efficient than trees at turning CO2 and water into carbohydrates. This is an error. Grasses are the primary C4 plants, while most shrubs and trees use the older C3 photosystem. I don't know if this is a typo; it should have been caught by the copy editor at very least (The author had a copy editor, who is named in the Acknowledgements). Anyway, to my point: Prior to the evolution of C4 photosynthesis, CO2 content of the atmosphere was nearly always between 500 ppm and 2,000 ppm. C3 plants thrive best with at least 500 ppm. C4 plants can draw down CO2 below 100 ppm, at which point most trees won't grow at all. So, you folks out there that want to grow stuff to draw down CO2, use grasses, not trees. Even at today's CO2 level of 440 ppm, the trees are struggling.

My favorite chapter is 3, "The Forest Primeval", in which the author lyrically describes aspects of life in the Carboniferous Era (as it is called in Europe; in North America this era is divided into the Mississippian and Pennsylvanian Eras).

This image I generated using Seedream V4.5 in OpenArt is not as densely packed with trees as I wanted, but it shows the alienness of the treelike species that existed at the time. Of course, I had to include an eagle-sized dragonfly. The rapid profusion of plants and their equally rapid burial, which formed our coal beds, led to a very high level of atmospheric oxygen. As the author points out, the larva of the dragonfly needed to be larger to reduce oxygen toxicity. Yet the extra oxygen also fueled the energy needed for the adult to thrive at its meter-sized length.

Had I been the publisher's editor, I might have amended the book's title to just The Earth was Green. This image of the Blue Ridge in Tennessee, from a panorama by the National Park Service, shows that Earth is very green even today:

Riley Black is a trans woman, who put the pronouns "she/they" in the author bio. Since she is at least halfway through a full physical transition, I'm willing to say "she". "They"? Not so much. I care about singular and plural. Her pronoun confusion extends to the grammar of the book, where it is applied to the creatures. Sentences with wording such as, "Now that the monkey can reach the fruit, they can…" are simply solecisms. The common usage is "it can…", which is at least genderless. Similar grammatical errors are found numerous times per chapter. It is sad. Apparently her copy editor shares her grammatical mis-education.

Ms Black's writing is lyrical and enjoyable. She has published several earlier books, and I understand all are popular. And I envy her access to so many prime fossil localities!

One last quibble: In the first chapter, describing how DNA data are mutated, the analogy of a copy of a copy of a copy in a photocopier is used. It's a very bad analogy. The successive copies gradually fuzz into meaninglessness. No new letters appear. In DNA, every "word" is exactly three letters. Every possible combination is meaningful. A DNA copy error doesn't make any fuzz, it exchanges one letter for another, or it may even add or delete a letter, causing a frame shift (frame shifts are fatal flaws).

Volcano viewing is going on my bucket list

 kw: book reviews, nonfiction, earth science, geology, volcanology, planetology

My uncle was a professor of geology. He had a "volcano fund". Whenever he got news of an interesting volcano beginning to erupt, he would try to go to see it. This often required getting someone to fill in for him to teach a few days of classes. He had to be selective, with 20-40 or more active volcanoes spouting off on any given day. For example, "interesting" included "rather safe" and also, erupting day after day to give him time to get there and have a good chance of seeing the eruption in progress.

On the other hand, although I have degrees in geology, I have never seen a volcano erupt. Time's-a-wastin'! I'm not getting any younger, so I'd better get on the volcano grapevine. A big component of that grapevine is the Current Eruptions page at the Smithsonian Institution, something not available when my uncle was alive. The map shows the current situation as of April 15, 2024, of volcanoes that are "in continuous eruption", but you need to read the definition of continuous…

Dr. Robin George Andrews is certainly on that grapevine. He's in the enviable position of being able to go see volcanoes pretty much at the drop of a hat. His book Super Volcanoes: What They Reveal about Earth and the Worlds Beyond brings us very informational stories about what volcanoes are, where they are to be found, and how they help us discover the dynamics of a planet. By the way, note that the title is not Supervolcanoes but Super Volcanoes, as in "Volcanoes are Super" but with a less juvenile connotation. Supervolcanoes, including Yellowstone caldera, occupy one chapter.

An example of seeing the dynamics of Earth is quite visible in the map above: the "ring of fire" around the Pacific Ocean. This has been known about for centuries, but it was only explained after the discovery of plate tectonics in about 1960 by Marie Tharp and others. The Pacific Ocean is slowly shrinking, being "subducted" under moving plates bearing the continents all around it; the Atlantic is growing at the same rate. The motions are mostly in the range of 2-5 cm/year, about the speed a fingernail grows. The very different style of (now extinct) volcanism on Mars and Venus indicates that plate tectonics did not happen on those planets, or if it occurred very early on, it didn't last long, and hasn't operated for at least three billion years.

By contrast, this image of the moon Io shows us a smallish body with a surface that consists entirely of volcanoes and lava flows. The blue plume is an erupting volcano. Although Io doesn't seem to have plate tectonics, it is kept hot (about the boiling point of sulfur: 445°C or 832°F). How? Its orbit around Jupiter is elliptical, and the orbit is kept from being "rounded out" by resonance with the orbits of its sister moons. The elliptical orbit results in tides that stretch and squeeze Io, heating it halfway to boiling in the process. For the curious, Io is pronounced "EE-oh".

You may have heard that some of the moons of Jupiter and Saturn have subsurface oceans, probably of salty water beneath a thick (20-50 km) crust of ice. Io has a subsurface ocean of molten rock! Actually, it is kind of a slushie with crystals of high-temperature minerals in a broth of lower-temperature mineral melt.

Earth has three ultra-famous volcanoes. One of these is Kilauea, in Hawaii. It is huge, and it tends to erupt more than half the time. For the past several days it has not been erupting, but mini-earthquakes are going on all the time, indicating that magma is moving around beneath the crater. It could start again any time, and it might then erupt for a few days, or months, or even several years.

The most beautiful volcano, in the eyes of many including me, is Fujisan in Japan. It is often called Fujiyama, but in Japan most mountains are given the suffix "san" rather than "yama". Both suffixes mean "mountain". This view is from the southwest end of Ashinoko ("foot-shaped lake"), in the Hakone area, a national park. I have seen this view from this spot, but in the springtime, when these maple trees were green. Fujisan is considered dormant, but it is not entirely inactive. Its most recent eruption was in 1707.

The most feared volcano by many, the one usually called a supervolcano, is the Yellowstone caldera in northwestern Wyoming. This is one of several, probably at least 20, on Earth. The Supervolcano page of Wikipedia states that at least 60 "VE8" eruptions are known to geologists. The Volcano Explosivity Index is logarithmic, and the biggest events, dubbed VE8, yielded at least 1,000 cubic km of ejecta, either lava or ash or both. The most recent such eruption was 26,500 years ago in New Zealand. Of the five known VE8-size eruptions by the Yellowstone hotspot, which has moved across the northern US for 40 million years, the most recent was 640,000 years ago, and barely makes the grade as a VE8. The largest known eruption from this hotspot occurred just east of southern Idaho, and was about three times that size, 2,800 cubic km. That makes Yellowstone a rather small supervolcano! At least four supereruptions elsewhere exceeded 5,000 cubic km, and two, one in Canada (half a billion years ago) and one in Indonesia (75,000 years ago), may have exceeded 12,000 cubic km of ejecta. For reference: the abyssal plain of the Ocean has an average depth of about 4.5 km, so 12,000 cubic km would fill 2,650 sq km of the ocean, or about 40% of the area of Delaware or 65% of the area of Dubai.

The author discusses the Yellowstone hotspot and other hotspot supervolcanoes for a full chapter, and tells us we have little to fear from Yellowstone. The hotspot's current location is at the eastern edge of the Yellowstone Caldera, and it is moving eastward a few cm/yr. To be accurate, hotspots don't actually move, the continents above them move. The North American Plate is moving almost due westward, while the Yellowstone hotspot periodically pushes magma into the crust and starts a new volcanic province, at intervals of about a million years. The current motion is bringing a thicker piece of very resistant crust over the hotspot, and it may not be able to cook its way through the crust again until the rest of the continent crosses over it, in 60 million years or so.

There is much, much more, but this is a taste. Super Volcanoes is super fun to read. A final volcano image, this one imaginary:

The "bugs" that ruled the Paleozoic

 kw: book reviews, nonfiction, science, geology, paleontology, trilobites, paleozoic era

If there were no dinosaurs, everybody's favorite fossil animals would be trilobites. Soooo, they are second-favorite. They are not big like dinos. Most are between an inch and 4 inches long (25-100 mm).

What they lack in size, they make up for in panache! They had eyes (most of them), lots of legs, and a distinctive, unique look.

Though they vaguely resemble familiar animals such as horseshoe crabs and pillbugs (roly polys or woodlice), the last trilobites became extinct 251 million years ago. They have no modern descendants.

The three "lobes" of their designation are not arranged front-to-back, as many assume, but side to side. The central lobe is flanked by a right and left lobe consisting, in front, of cheek plates, and behind, of shell plates that covered the legs. A tail-end called a pygidium may be no more than a tiny blob, or may be as large as the head (called a cephalon).

Literally the most common trilobite is named Elrathia kingii. These attractive "bugs" are found in rocks  of middle Cambrian age, 515-499 million years old. Most specimens are found in Utah, with shells consisting of very dark gray calcite on a lighter gray matrix. They are rather small, usually an inch (25 mm) or less, but range up to 1.6 inches (39mm).

This is enough to whet the appetite a little. The range of species is immense: 25,000 named trilobite species so far, ranging from the early Cambrian, 521 million years ago, to the end of the Permian 251 million years ago, when they and many other marine animals were wiped out in the Great Dying that killed 99% of everything.

Several hundred species are pictured in Travels with Trilobites: Adventures in the Paleozoic by Andy Secher. Mr. Secher is one of the premier collectors of trilobites, having more than 4,000 specimens. Many of the photos in the book are of specimens in his collection. He is affiliated with the American Museum of Natural History as a Field Associate.

The book is arranged first by time. Trilobites are such a characteristic marker of Paleozoic rocks that it made sense to set chapter by chapter in the periods of the Paleozoic era. Four Chapters cover the Cambrian, Ordovician, Silurian and Devonian periods. A single chapter covers the rest, the Carboniferous and Permian periods, as they are known worldwide except North America, where the Carboniferous is divided into Pennsylvanian and Mississippian periods. The reason for this grouping is that trilobites were becoming less common, and many orders and families had gone extinct by the beginning of the Carboniferous period.

Within each chapter we find extended treatments of classic and prolific collecting localities. Naturally, the unequalled Burgess Shale, of middle Cambrian age, around 508 million years ago, is discussed in loving detail in the Cambrian chapter. Interspersed among the locality descriptions we find topical subjects such as "Trilobite Soft Tissue Preservation" (The Burgess Shale was the first major locality of this kind, preserving much more than trilobites) and "Trilobite Enrollment" (they could roll up like pillbugs or armadillos). Each chapter ends with several "Rapid Reports" of localities not discussed in detail, and a photo gallery of specimens from the chapter's geological period. The page below is from the Ordovician chapter.

These photos illustrate some of the variety of preservation styles. While these are among the best specimens in existence of their respective species, they show how some trilobites are more flattened, and some have been preserved in the round.

If you go to any locality where trilobites are common, will you find specimens this beautiful? It's rare. Mostly what we find are portions of the shell. For every trilobite that died intact and was preserved whole, there are thousands or millions of shell parts from molting. Their shells had sutures, as do the shells of crabs; periodically the animal would pop off the shell in parts, and, as rapidly as possible, grow a larger one. They were very vulnerable in the "soft shell" condition…as are soft shell crabs!

When a complete trilobite is found, it is seldom all visible. The first illustration above, for example, shows how a preparator had to remove surrounding material to expose the animals. The one in the upper middle, for example, was at a different depth (I don't know how the preparator knew that), so a lot of matrix had to be removed to reveal it.

Preparators are the behind-the-scenes heroes of the trilobite trade. They may start with a nodule that shows nothing more than a couple of tiny spots of shell, and spend hours removing material until the whole is exposed…or not. Many times the result is not what was expected. But they soldier on. A specimen such as this one requires a lot more work than the flatter ones most of us are accustomed to. This is a Walliserops, found in Morocco, where in recent years many incredible 3-D specimens of many species have been unearthed.

The last chapter of the book touches on many topics, including preparation. One side matter is "Fake Trilobites". Some preparators are more sculptors than extractors. If you want to buy some of the more common trilobites, you have little to worry about. But with others that are more rare, well, watch out. Get help from an expert!

Rather than go on and on, let it suffice that this almost-coffee-table-size book is well worth reading, well worth looking over again and again, and a terrific introduction to these fascinating Paleozoic "bugs".

The billion-decade pie recipe

 kw: book reviews, nonfiction, geology, cosmology, astronomy, nucleosynthesis, cooking

This chart was mentioned in How to Make an Apple Pie From Scratch: In Search of the Recipe for Our Universe, From the Origins of Atoms to the Big Bang, by Harry Cliff. The book's title, indeed its raison d'être, is a humorous aside by Carl Sagan on an episode of Cosmos: "If you wish to make an apple pie from scratch, you must first invent the universe."

Harry Cliff is a particle physicist and researcher on the Large Hadron Collider, specifically the experiment/detector called LHCb. The "b" means "beauty", for the Beauty Quark, which most physicists now call the Bottom Quark (the "t" and "b" quarks were initially called "truth" and "beauty"). The short answer to "What is 'scratch'?" would be, "Something smaller than a quark." Quarks are what we call the (possibly) indivisible bits that make up protons and neutrons, which with electrons, form atoms.

I think of the book as a microscope that uses higher and higher powers to probe the makeup of the universe. Dr. Cliff actually began his investigation by obtaining an apple pie and pyrolizing a few grams. That gave him a rough estimate of the phases present, gas/vapor, liquid, and solid. The final product of pyrolysis is charcoal, although he found later that he didn't cook it hot enough; his charcoal still had some volatile stuff in it. It matters little: the end product was mainly carbon, the "gateway element" to producing the entire suite of elements from hydrogen and helium. The chart above shows the various "ovens" in which the elements were made.

Much of the book is history, the history of the discovery of the chemical elements during the Enlightenment, then the discovery of subatomic particles a bit more than a century ago. Although I've read the stories again and again (because writers seem compelled to cover it all every time), I find it enjoyable to rehearse the way alchemy became chemistry, and experiments with "cathode rays" and pitchblende came together to discover that atoms (from "a-tomos", "un-cuttable") are actually cuttable, and the "easy" sub-parts are further cuttable.

The book skips over the range of magnification available to a light microscope. There is nothing about the plant cells in the apples, or the microstructure of a perfectly baked crust. We go from some burnt pie right to atoms, which can only be distinguished when the magnification exceeds 10,000,000X, the magnification of this STM image. The best electron microscopes are hard pressed to deliver magnifications greater than 1,000,000X. Thus STM, or Scanning Tunneling Microscopy, has to be used. The white spheres here are atoms of lead, on a silicon surface.

The reason for this omission is soon apparent. The author's quarry is smaller compared to an atom of lead than that atom is to a sports arena.

An ordinary light microscope "maxes out" when viewing items smaller than half a micrometer (or micron, or µ). An E. coli bacterium is about 2µx6µ. The photons of green light, with a wavelength of 0.55µ, have an energy of 2.25 eV. One eV, or one electron volt, is the energy of an electron that has "fallen" across the gap between an anode and a cathode when the voltage is 1V. Photon energies in the range 1.75 eV to 3.1 eV are used by the retinas of our eyes to detect "light". Things smaller than about 0.5µ, or 500 nm (nanometers), can only be studied using "light" of a shorter wavelength. And here is the important principle: shorter wavelength means higher energy per photon (or other particle).

Why is it hard to "see" an atom? It is because they are so much smaller than the wavelength of visible light. The lead atoms in the image above are about 0.35 nm across. That's 0.00035µ. The silicon atoms in the surface below them are much smaller, with an interatomic spacing of 0.078nm. An electron microscope with beam voltage of a million volts uses electrons with energy of 1 MeV (million eV), and a wavelength of 0.0012 nm. However, such an electron beam simply blows off most of the electrons from the atoms you want to look at, while a more "modest" beam of about 16,000 volts, and a useful magnification of a million, can produce images without causing total disruption. The STM technique sidesteps this by using atomic forces to get higher-resolution information, with a limit in the range of 10 to 20 million X magnification.

When the biggest constituents of atoms were discovered, electrons, protons, and neutrons, they were soon found to be a whole lot smaller than the atoms. One analogy states that an atom of hydrogen magnified to the size of a stadium (a magnification of two trillion) would be "seen" to be an electron cloud with a speck at its center the size of a small pea, perhaps 6mm diameter: the proton.

How do you "see" a proton? Since it is about 50,000 times smaller than the atom, you would need 50,000 times the energy. At a minimum, 16,000 eV x 50,000 or 800,000,000 eV, just under a billion eV (GeV). Now, let's think a minute. A million-volt power supply needs a lot of insulation. In radio, the rule of thumb is that in dry air a spark will jump about a centimeter per 10,000V. So a million-volt potential can jump at least a meter. I remember seeing a picture of an early million-volt electron microscope. It was eight feet high. What do you do with a billion volts? Such a voltage can jump a few miles. Indeed, lightning has voltages in the billion-to-ten-billion-volt range.

Here it gets fun. Particle accelerators finesse the situation by using magnets and rhythmic pulses to take a bunch (that's the scientific term) of electrons or other charged particles from an "easy" energy of 10,000 eV to higher and higher energies. It's sort of like swatting a tetherball again and again to make it go around faster and faster, except these "tetherballs" are soon going 99% of the speed of light, or more.

When I worked at Cal Tech (as a machinist), I worked part of the time in a room with a dismantled synchrotron about 30 feet in diameter. Energetic electrons or protons lose energy when you turn them to go around in a circle, so the more energy you want, the bigger the circle has to be. The LHC, where Dr. Cliff works, is about 8.5 miles in diameter. It produces beams of protons with energies that exceed 10 trillion eV. It also runs them in both directions, and steers them into head-on collisions, so you get enormous penetration. All that to "see" the insides of particles a few thousand times smaller than protons, which is what it took to prove the existence of the Higgs Boson (but not see into its insides…if it has any).

Chapters and chapters earlier, the author discussed where the atoms came from. The chart that begins this article shows where. Things we can eat, and we ourselves, are primarily CHON, that is, Carbon, Hydrogen, Oxygen, and Nitrogen. Hydrogen makes up 75% of the weight of the matter in the universe. Or, at least, of the matter that is either visible or potentially visible because it can respond to electromagnetic energy ("light"). We need to ignore dark matter and dark energy here, because we still have no idea how to interact with them. Most carbon and nitrogen are made in "dwarf" stars, main sequence stars smaller than 1.25 times the mass of the Sun. The jury is still out on whether the white dwarf stars that result from the demise of a main sequence dwarf star have to be blasted apart to release carbon and nitrogen, or if the red giant phase releases enough to amount for what we see in the sky. Most oxygen, at least most of it that gets into the interstellar medium, is forged during supernova explosions. So at an atomic level, that's where the basic ingredients of the apple pie arise.

The reason for using big atom smashers like LHC to dig into the protons for their smaller bits (quarks and gluons, mainly), and into the quantum fields that modulate (or create) their properties such as mass, is that we aren't really back to "scratch" yet. By the end of the book, if we have understood it all (I am not quite there yet), we have the beginnings of matter traced back to the end of the first one-trillionth of a second after the Big Bang. 

Does that sound pretty good? Not to a cosmologist! The Big Bang is thought to have begun with everything we might call space and time located within a radius of about the Planck Length, which is about 1.6x10^-35 meters. The initial "Bang" got rolling in Planck Time, or about 5.4x10^-44 seconds. Let's just call it 10^-45 sec., and compare it to a trillionth, or 10^-12 sec. There are about 10³³ Planck Times in a trillionth of a second; a little matter of a billion trillion trillion of them. A lot happened that we will be hard pressed to probe. The author describes the ultimate particle accelerator, wrapped around the center of the galaxy (where it has a chance of being gravitationally stable), with a diameter of several thousand light years. The biggest we have a chance of building might wrap the Earth at the equator. The particle bunches would circle the planet seven times per second, so we have long enough lives to do experiments with it, with energies as high as perhaps 50,000 TeV. That's still a long way from the Planck Energy, but it might be close enough to be "interesting".

Future beings with very long lifetimes—because each experiment takes a million years or more—might probe the Planck Length using the Galactic Collider. But beyond a certain level of energy, the only output of the experiment will be tiny black holes. According to Hawking's principle, such a black hole would soon explode into a shower of energetic particles, but they would carry no information about what was going on inside, so the fancy machine would simply be a huge fireworks generator.

The book ends with a description for beginning from scratch, to the point where matter exists, including a middling size planet with apple trees and wheat fields and such. Then it ends with a pretty good recipe for making an apple pie. There ain't a quark anywhere that can explain the great taste of fresh apple pie.

The biosphere has used five of its lives

kw: book reviews, nonfiction, geology, geologic history, earth history, mass extinctions

Beginning Geology students have to learn a plethora of new terms, including the geologic ages: Pre-Cambrian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous (in the US, divided into Mississippian and Pennsylvanian), Permian, Triassic, Jurassic, Cretaceous, Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Recent. I remember learning a letter-mnemonic for Cambrian through Recent: COSDMPP-TJC-PEOMPPR. Over time we learned that each such age has characteristics that differ from the others, including different prevalent rock types and different fossils.

Later on we learned that the significant differences from age to age are a result of great revolutions in the kinds of living things, and the transitions are marked by large increases in the rate of extinction. Further, five of these are called "the Big 5" and "the Great Extinctions". Here is a summary of these as shown in a poster prepared by Bud Charles, in use by many web sites that discuss "the Big 5"

The "Death Rate" reported in the diagram is the number of species that were driven to extinction. The percent of the biosphere that was destroyed is a much harder quantity to determine, and I have not found any published estimates. Considering the certain damage to each species that survived any of these events (or periods; some "events" took a million years or more to unfold), it is likely that the actual reduction in the "living biosphere" was 90% or greater for each of these, and may have exceeded 99% for the biggest, the end-Permian mass extinction.

The recent book The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth's Past Mass Extinctions, by Peter Brannen, is a very well-written travelogue through the geologic ages, focusing in some detail on the processes of each of the Big 5. The photo plates show scenery of the existing geology resulting from them. It would have been very beneficial to have a chart such as that above, with even more detail, because more is known now (in 2017, the date of publication), compared to just a few years earlier when the poster was produced.

It would also be useful to have a visual of where these fit in time, such as this diagram from an article in the Washington Post, reproduced here at a small size as allowed by copyright law.

The section on the right labeled "Tertiary" includes all the ages from Paleocene to Recent. The dips and wiggles show how extinctions less severe than the Big 5 have played a part in the transition from each age to the next. Also, the little dip in the middle of the Carboniferous represents a significant change in plant life that accompanied a lesser extinction event, which marks the divide between the Mississippian and Pennsylvanian ages as recognized in the US.

In this diagram, the metric is "number of families", rather than number of species. Look particularly at the end-Permian, where the number of families has dropped by about half, as compared to the number of species, which, as noted above, dropped by 95% to only 5% of its former value. The taxonomic Family is two levels broader than the Species, so if even a single species in a family survived, that is a surviving family. Nonetheless, the end-Permian event is clearly the most severe.

The kinds of things that nature can throw at Earth and its biosphere are described clearly in the book. In many cases, the primary causes may differ, but the critical factor is a great change in global temperature. In the chart above, "rapid global cooling" is mentioned twice, and "rapid global warming" is mentioned twice. In the case of the end-Cretaceous event, it is likely that almost instant world-wide broiling occurred, followed by decades or centuries of "impact winter".

Three of the Big 5 were caused, at least in part, by the eruption of flood basalts, a tame term for the sudden release of 100,000-1 million (or more) cubic miles of lava. Even the end-Cretaceous event, which destroyed all the dinosaurs (except a few that became birds) plus the flying and aquatic reptiles, which "everyone knows" was caused by an asteroid crash 65 million years ago, coincided with the eruption of the Deccan Traps ("Trap" is another word for flood basalt), in India. Enough is known about the Deccan Traps to calculate that if the lava had been evenly spread over the Continental US, it would have been 600 feet deep. That makes the scale of the Yellowstone "supervolcano" a cap pistol by comparison. As big as that was, the Siberian Traps that we think were the primary cause of the end-Permian extinction, 251 million years ago, were as much as ten times larger. The third flood basalt event left remnants in New Jersey (the Palisades) and around the East Coast of the US at the end of the Triassic about 200 million years ago. It was smaller than the Deccan event, but big enough to rate as one of the Big 5.

What can cause volcanism on such a scale? Generally speaking, the splitting of a continent will fill the bill. Prior to about 1966, the continents were thought to be stable and immobile, and all kinds of wild ideas were in vogue at various times to explain the origin of mountains. Plate tectonics was "discovered" in the early 1960's, after being proposed in 1912 by Alfred Wegener, and just when I began to study geology in earnest (1970), this new paradigm changed everything. It was an exciting time to study geology. One offshoot was the study of supercontinents. They seem to form periodically.

The mid-Atlantic Ridge is pushing that ocean's coasts apart at a rate of 2.5 cm/yr., which amounts to 25 km per million years. The Atlantic Ocean's width varies from under 5,000 km to 6,000 km or so, which implies that the breakup of a supercontinent that once included Africa, Europe, and the Americas adjacent to one another along a "seam", occurred beginning about 250 million years ago, and was completed after 200 million years ago. That 250 million-years-ago figure is suspicious. Another "seam" appears to have ruptured at the same time thousands of miles away, and apparently it was the more "active". That would be the source of the Siberian Traps. The 200-million-years-ago figure, relevant to the Equatorial Atlantic, would point the finger at the end-Triassic event that covered much of the eastern US with lava. I think that is enough to make the point.

The mid-Atlantic Ridge isn't the fastest. The Pacific Plate is presently being absorbed under Asia at a rate of 8 cm/yr or 80 km/million years. Other plates are moving in other directions, with Africa as an apparent pole of stability. Other plates and their continents show evidence of passing over hot spots in the mantle, such as the one that produced the Hawaiian Islands and the Emperor seamounts, the one currently under Reunion Island, and the one that produced Yellowstone and a chain of calderas stretching at least as far as Idaho. Africa doesn't seem to have any hot spot traces, but it is apparently beginning to rift apart near its eastern margin, in the beginnings of another cycle of continental splitting. 

The crust of the Earth undergoes cycles of continental mash-up into supercontinents, followed by fragmentation. Note that we are in an era of partial fragmentation; Asia occupies about 2/3 of all the continental area of the Earth, and is likely to gather the rest of the continents into one after another 100 million years or so. The Pacific Ocean is shrinking at a rate of about 80 km/million years, so it won't last forever!

Considering this, I wondered if the breakup of earlier supercontinents might be implicated in other big extinctions. Here is a list, summarized from several articles and other documents. Note that Pangaea spans the end-Permian and end-Triassic extinctions. I find it curious that Pannotia came together just after the Deccan Traps erupted, so perhaps continental construction is as effective as continental splitting at producing biosphere-threatening volcanism.

The earlier supercontinents occurred before the Cambrian, which means before easily-found fossils. They could not have been involved in the Big 5. But there were earlier mass extinctions; they are hard to detect, because only bacteria (and archaea) lived then. I suspect a number of Precambrian great extinctions happened. Numerous Precambrian geology specialists are busily working on it.

Atmospheric chemistry is a different driver of extinction. It may be that the biggest mass extinction of all occurred when oxygen began to accumulate in the atmosphere. Photosynthesis began about 3.5 billion years ago. There are several types of photosynthesis, and at first, only one, called "C3", found today in algae and most plants, produced oxygen directly. Other types, such as that used by green sulfur bacteria and purple sulfur bacteria, have other chemical results. For a billion years, none of the oxygen made it to the atmosphere. It was all consumed oxidizing iron and its sulfides, and other reduced materials, forming the great "red beds" and other oxide ore accumulations, for example. About 2.5 billion years ago, most reduced materials had been oxidized, and oxygen began to enter the atmosphere.

We can see from this chart, found in Wikimedia Commons, that a low level of oxygen, in the 3%-5% range, prevailed for more than a billion years, and it seems life kind of stagnated once it got used to that. This era is called the "boring billion." The upward inflection shown here at about 900 million years ago probably occurred a little earlier, maybe at 1.1 billion years. The red and green lines are limits proposed by various workers; the red line is the more probable.

Animals and plants apparently evolved just about a billion years ago, with a metabolism fueled by increasingly abundant oxygen. The big uptick occurred during the Permian, when oxygen probably exceeded 30%, compared to 20% today.

The other significant gas is carbon dioxide, CO2. This is one of numerous diagrams showing the level of CO2 over the past 600 million years. In The Ends of the World it is stated that the primary mechanism for absorbing CO2 is weathering of basaltic rock. However, it is slow, taking place on a scale of 100,000 to a million years. Based on this chart, one would expect that fresh basalt was made available in the mid-Cambrian, all during the Ordovician and Silurian ages, and in the early Carboniferous. That doesn't seem so. Rather, in particular for the Carboniferous age, the huge expansion of forests that produced nearly all the coal in the world occurred. I'll leave it at that because this is a side point.

Apparently, the dip in life's diversity in the mid-Carboniferous that I mentioned earlier happened when CO2 was drawn down to modern levels (between 200-400 ppm), at which point trees, which rely on C3 photosynthesis, have a hard time growing rapidly. At the far right, the CO2 drawdown that trended during the Tertiary (Paleocene until the present) was apparently a result of new types of green photosynthesis, called CAM and C4. Grasses, the main sort of C4 organism, and their relatives are very happy with 200 ppm of CO2 or less, while trees are happiest when CO2 is in the 1,000 ppm range. Experiments with rice plants have found that rice grows best when CO2 is 2,000 ppm.

The author makes much of the gyrations of CO2 that occurred in the past. While he is right in general, he tends to be alarmist. I almost added "polemics" to my labels for this review, but I decided not to. The book may get a little polemical, but it is much more than that, and contains a great amount of interesting and useful information about the worlds that preceded us, particularly how different each one was from what we live in now. For example, we are accustomed to reefs based on hard corals that host mollusks and fishes of many kinds. Permian reef backbones were masses of brachiopods and mollusks, with corals scattered among them, hosting more ammonites than fishes. Cambrian reefs were even more weird, made of piled-up animals that looked like individual coral polyps, lots of brachiopods (they look like cockles, but with much lower metabolism), and the main swimming things were trilobites and nautiloids, which look like straightened out ammonites (both resemble squids with big shells).

I was particularly interested in the analysis of one person cited, who said we are nowhere near a sixth great extinction. He has the numbers to prove it. So it is a little early to call the past century or two the beginning of the Anthropocene age. But we would do well to be wary. The greenhouse effect is real, and it is pretty certain that we are contributing to it. Whether it will lead to catastrophe or instead ameliorate the next ice age is yet to be seen.

How much can we heat the planet if we continue to burn petroleum and coal? As a teen I reproduced the calculations of Arrhenius, the one who first publicized the CO2-induced greenhouse effect. Later, using differential-albedo modeling (such as how sunlight heats something that absorbs visible light better than infrared, or vice versa), I verified something I read: "If we push CO2 so much that we 'close' the 'window' of its absorption bands in the infrared, the maximum warming would be 4°C". Statements about 9°C and even 12°C are not realistic, nor mathematically possible. Now, four degrees is significant. Will it melt Antarctica? Probably not.

We are also not going to push CO2 into the tens of thousands of ppm range, just by burning fossil fuels. Some look at the oxygen in the atmosphere as being entirely "carbon debt". That 20% is 200,000 ppm. CO2 weighs 37.5% more than oxygen does. If we could really extract (and burn) that much carbon from oil and coal fields, the actual mass of the atmosphere would increase 7.5%, and this new, heavier atmosphere would be 25.5% CO2, or 255,000 ppm. We would all have died from anoxia long before that point. But the total extractable carbon in the crust is only a fraction of this, a few percent. Most of the carbon from decaying "stuff" was carried into ocean trenches and is deep in the mantle, perhaps making gigatons of diamonds!

I have a quibble of a different nature: on page 189 it is stated that the asteroid that did in the dinosaurs "put a hole in the ground 20 miles deep—deep enough...to puncture the earth's mantle...". This should state "puncture to the earth's mantle", which begins around 20 miles down, and extends 1,800 miles deep.

On a happier note, the author cites Mark Richards as proposing that the asteroid impact actually triggered the formation of the Deccan Traps. A more modest level of flood vulcanism had begun before the impact, but it took off right at that time. I suggested this to one of my geology professors some 40 years ago, and he was very skeptical. At that time the "impact theory" was accepted, but the location of the crater in Yucatan wasn't yet known. I suggested a possible impact antipodal to India, somewhere in the South Pacific, perhaps 1,200 miles southwest of the Galapagos Islands. Dr. Richards does say that an antipodal arrangement would yield the best "focusing" of the seismic disturbance caused by an impact, but since the asteroid's impact was like a magnitude 11 or 12 earthquake, such focusing was not needed to trigger an ongoing eruption into a mega-event, releasing its pent-up lava over a much shorter interval.

Another significant theme is that all of the Big 5 mass extinctions were multi-factor "perfect storm" sorts of things, with the end-Permian event being the "most perfect". I'll leave that for readers to discover as they enjoy this readable and informative book.

Stories rocks tell

kw: book reviews, nonfiction, geology, geologists

I was in college 14 years, educated mainly in geology. Funny thing: graduate school ruined geology for me as a profession. So I returned to rockhounding as a hobby, and earned my keep by writing software for geologists and other sciences; I had enough classwork in the "hard" sciences to get majors or minors in them all. But reading the writing of Professor Donald R. Prothero made me nostalgic for what might have been. However, I judge that Dr. Prothero is quite a bit more talented than I in big-picture geology, and the long shelf of his books on the subject attests to that. The oldest book of his currently on sale, a major textbook, Interpreting the Stratigraphic Record, published in 1990, still sells for about $128.

Today's book, however, is much more accessible (and less costly!) than the text: The Story of the Earth in 25 Rocks: Tales of Important Geological Puzzles and the People Who Solved Them. (That's not the longest title I've seen, but it is close.) We can take the word "Rocks" in the title rather loosely, since one chapter is on the San Andreas Fault, all 800 miles of it, and another is the first stratigraphic sequence and the first geologic map, produced by William Smith in England in the early 1800's. However, actual rocks aplenty are dealt with, from tiny zircons used to determine the ages of ancient rocks to meteorites, coal and the tin oxide mineral Cassiterite that led to the "tin can" and "tinfoil", before aluminum (aluminium to the English) became cheap enough to replace tin.

This is the story of the earth, after all. The stories of the rocks are secondary to the earth processes they reveal. The San Andreas fault, seen here where it crosses Carrizo Plain National Monument about 100 miles north of Los Angeles, is flanked by rocks that can be matched up across it. Except "across" is a flexible term: the rocks found on the left (SW) side in this photo from Wikipedia match up with rocks found on the right (NE) side about 200 miles further south, northeast of San Diego. The chapter on transform faults, near the end of the book, which uses the San Andreas as its poster child, reveals how such faults fit into the puzzle of large-scale tectonic movements that we now call Plate Tectonics. Other chapters use other rocks and rock phenomena (such as magnetism) to bring together other pieces of this biggest of earthly puzzles.

Going to the opposite end of the size spectrum, the tiny crystals in this photomicrograph, of a field of view just 2 mm wide, are zircon crystals, extracted by dissolving a piece of granite pegmatite (granite with large crystals) with hydrofluoric acid. The image is from this publication by Thomas E. Krogh et. al. on ResearchGate.

Zircons are very valuable geologically because they often contain most of the uranium found in granite and similar igneous rocks, and their robust structure keeps all the daughter elements from uranium's breakdown, so that measurements of the ratio of uranium to lead can tell you the age of the zircon, and thus of the rock it came from. Beware, though: zircon crystals are also found in sedimentary rocks, and do not tell you the age of those rocks, but the age of the rocks in which they first formed. As long as you know this, they are still useful. You just need to know what you are doing.

Just by-the-by, the oldest piece of rock found on Earth is a tiny zircon crystal with an age of 4.4 billion years. The half-lives of U-238 and U-235 are 4.5 and 0.7 billion years, respectively. The final product of U-238 is Pb-206, and that of U-235 is Pb-207. Thus, since the time that ancient crystal was formed, nearly half its U-238 turned to Pb-206, and all but 1.3% of the U-235 turned to Pb-207. A zircon that contains more atoms of lead than of uranium is going to be very old.

The overarching theme of the book is the gradual development of the foundational "sphere" of Earth System science (Geosphere, Hydrosphere, Atmosphere, Biosphere, in decreasing order of mass). When I was a child the development of mountain ranges was explained as the wrinkling of a thin "skin" (Earth's crust) as the planet shrank while it cooled. The analogy was made to an uneaten apple that gets wrinkly as it dries out. When I first took an Earth Science course in high school, there was talk of orogeny (mountain building) as being a side product of geosynclines, based primarily on vertical motions. I do recall someone remarking that the coastlines of Africa and South America seemed to match, and I first heard of "continental drift" at that time, maybe just before 1960. Only after I became a geology major (my third major) in 1970 did I learn of plate tectonics, in which the continents don't just "drift" but are moved along by a "conveyor belt" system, riding in the midst of enormous basaltic plates, driven by a combination of sea-floor spreading at diverging plate boundaries and subduction at converging plate boundaries. Now the analogy is a pot full of thick syrup with a sugary crust on top, heated from the bottom so it convects slowly, moving chunks of the crust about.

At one point or another, every chapter of this book ties back to the plate tectonic system. And why not? It is the whole-Earth process that literally creates geology. To see a planet without tectonic motions, look at Mars. The early loss of that planet's water and 99.4% of its atmosphere pretty much halted major erosion, so that we see a 3-4-billion-year-old landscape with two major kinds of features: one very big canyon (and a few smaller ones), formed as the last of the waters dried up, and a few enormous volcanoes, three times the height of Mount Everest. Oh, and there is a scattering of impact craters gathered over the past few billion years; though there are many, they are much less abundant than craters on the Moon, because Mars did have an eroding atmosphere and hydrosphere for its first billion years or so.

At present, back here on Earth, the Himalayas, the Sierras, the Andes and a few other ranges are growing, the Rockies and Urals are at a standstill, and other ranges such as the Appalachians are eroding away. New features replace old features. This will continue, though at a slightly decreased rate, until the Sun becomes a red giant, and perhaps longer. In another 4.5 billion years, half the present amount of uranium will be gone, and only 8% of the present amount of the radioactive isotope of potassium (K-40) will remain. Crank these figures backward, and we find that radiogenic heating was six times as great as it is now about 4 billion years ago (4Ga in geologist-speak). So plate tectonics rocked along quite a lot faster when Earth was young.

I was rather charmed to notice that most of the photos in the book are credited to Wikimedia Commons. It is now possible to write a book like this one without spending months writing letters to people who might have photos of things you want to illustrate, and permission to use them. However, there are a few other signs of rapid production that caused me a bit of concern. No author should be without a good copy editor, as these three examples (only a few of a dozen or so) attest:

• Page 80, first paragraph: discussing Lord Kelvin's estimate of 100 million years as "the time since the Cambrian", it is stated that this is off by "a factor of almost 50". The Cambrian era began a little more than 500 million years ago, so a factor of 5 would then be the correct one. However, looking up what Kelvin actually wrote, I find that he considered 100 million years to be the age since the Earth cooled from a molten state. Here, the actual factor should indeed be something like 45. So the mention of the Cambrian is the actual error. One's copy editor must know something about the science, not just English usage.
• Page 130, Figure 12.4, a photo of the 4.4 Ga zircon I mentioned above, called a "microphotograph." No, it is a photomicrograph. A microphotograph is what you find in microfilm, where a page of text is rendered to a size of about 1 cm, or even in a "spy dot", in which the page is reduced to 1 mm. A photograph of something through a microscope is a photomicrograph. The error is common, but should not be found in a book by a scientist of this stature.
• Page 221, last paragraph: discussing the news reporter's adage, "If it bleeds, it leads", except in this instance, the word is spelled "ledes". That's one of several dramatic misspellings I found.

OK, I just had to scratch that itch.

Of most importance is the content. This book is a must-read by anyone with the slightest curiosity about the "solid" Earth, about rocks, about how mountains are formed, or about earthquakes. Dr. Prothero is an engaging writer, thoroughly fun to read, who imparts a great lot of information quite painlessly. We need more such teachers among us.

Geology on the habitable edge

kw: book reviews, nonfiction, geology, plate tectonics

A formative experience of mine took place in a wilderness area north of Twenty Lake Basin in the Sierra Nevada mountains. The second session of Summer Field Camp was held there, for six weeks. What could we accomplish there that could not be done in the suburbs? To do geology you have to go where the rocks are…that is, where it is easy to get to the rocks. Where I live, near the Pennsylvania-Delaware border, you'd typically have to dig or drill 50-100 feet to find anything approaching "rock" as we know it: The Columbia Formation consists of loose to poorly consolidated (that is, cemented) sand with sparse fossils of Cretaceous dinosaur bone. You need to go a lot deeper to get to actual "bedrock".

Thus, a dozen other Geology students and I spent half a summer in high mountains, among lovely scenery, because the bedrock, mostly granite and limestone, was right there at the surface. We could walk up to it and hammer off chunks to take back to the "library" tent and study. We were interested in the intersection between the limestone and the granite, studying "cooked" rocks called skarn.

To study bigger problems you need to go to places even more remote. In A Wilder Time: Notes From a Geologist at the Edge of the Greenland Ice, William E. Glassley weaves a narrative of discovery around four field seasons, each about a month long, along the Arfersiorfik Fjord in western Greenland. The camp area is at or near the little white arrow I placed at the middle of this image. The map pin is on Tunertooq Island, where significant evidence was discovered by the author and his colleagues.

He and two colleagues were working to gather evidence that the area had been a continental suture in the deep past, around two billion years ago. The deformed rocks in the area look very similar to other areas of mountain-building, but are so much older that some geologists wonder if it is possible. The short answer is, "hard rocks", what we call igneous and metamorphic rocks, form primarily when continents collide and thrust softer materials ("soft rocks" such as sandstone and limestone) deep into the crust and mantle. They are later brought to the surface by various mechanisms of plate tectonics, where erosion eventually exposes them.

Plate tectonics describes the movements of the crust of the Earth over time. The "plates" are large portions of crust, including thicker continental crust and thinner oceanic crust; there are 8 major plates and about 20 smaller ones. They are in constant motion, but the rates are slow and imperceptible without instruments: 10cm/year or less, averaging 4-5 cm/year. That is just slightly faster than the rate fingernails grow. But give it time: If the Earth had only two continents, and they had separated some time in the past and were moving first away from one another, at a rate of 5cm/yr each, but later toward another as they each circled halfway 'round, how long would it take until they collided? This is equivalent to asking how long it would take one continent to circle the Earth at a rate of 10 cm/yr. The circumference of Earth, 40,000 km, is 4 billion cm, so the time would be 400 million years. That implies that the crust beneath the oceans is formed and then consumed on a time span of a few hundred million years. Indeed, the oldest sections of oceanic crust are no more than 200 million years old (except for a small portion of older crust, ~300 million years of age, that was preserved in the Mediterranean basin).

New material is added to the oceanic crust of tectonic plates at divergent margins, AKA mid-ocean ridges. Iceland rides atop one of these ridges, which is why it is so volcanic. Where plates move toward one another, one or the other will be pushed downward and (mostly) consumed into the mantle beneath. Such convergent margins are also volcanic, such as the "ring of fire" around the Pacific Ocean. The volcanic activity is evidence of the energies involved in the convergence. Where the convergence brings together two major continents, you get mountain uplift. The Himalayas are still growing as India presses into the Eurasian plate. In the roots of mountain belts, remnants of the collided plates, including bits of oceanic crust, remain to mark the suture zone.

Greenland, where you can get to the rocks (most of it is under a mile or more of ice), has large areas of strongly folded rock, similar to that seen in the Alps, the Himalayas, and the Rockies. These are understood to mark the continental collisions that produce each mountain chain. The Appalachian mountains, including the area shown here in central Pennsylvania, are understood to be the roots of a mountain chain that stood tall 300 million years ago, but is now eroded to these remnants. By comparison, the Rocky Mountains were formed during the Laramide orogeny, between 80 and about 40 million years ago; the Alps began forming about 65 million years ago, and the process is presently winding down; and the Himilayas began forming about 40 million years ago. Each such mountain range has buried beneath it a suture zone where two continents collided.

The folded rocks in western Greenland are about 2,000 million (2 billion) years old. There is still some controversy among geologists about whether plate tectonics operated that early, or if it did, whether it worked the same way as it has in the past half billion years or so.

When I was a graduate student of Geology in the early 1980's, in one class we were asked how we would determine whether plate tectonics had operated in the early Precambrian, prior to about 1.2 billion years ago. I didn't do well on the assignment, and received my only C grade. Dr. Grassley and his Danish colleagues would have received an A+. They not only figured out how to do so, they went and did it, though it took a couple of decades. I think it no spoiler to report that the field seasons described in A Wilder Time led to a much better understanding that the Arfersiorfik Fjord area does indeed include a continental suture zone.

The book is in three parts, describing first the breaking down of old concepts, then accepting ignorance and becoming open to new ideas, and finally the beginnings of integration as a broader understanding emerges. The author stresses several times that our biology constrains us to awareness of only a tiny fraction of what the Universe has to offer. We "see" within one octave of a span of nearly infinite radiative wavelengths; we hear a wider range of sound frequencies, but most animals can hear sounds we cannot; we can bear only a narrow range of temperatures without severe damage; and so forth.

I was doubly compelled and fascinated by the book. I thoroughly enjoyed the geological material, of course. Even more, the author writes with a rare lyric intensity. He sparsely limns the emotions and impressions evoked by the harsh landscape. And sometimes it is not so harsh. One day he knelt and lay flat, to see the outline of a ptarmigan and her chicks hiding in plain sight atop the tundra:

I was suddenly awash in layers of sweet flower scents. As I rested lightly on the surface, the smell of dozens of blossoms I hadn't noticed engulfed me. Arctic poppy and white Arctic bell-heather were interspersed among mountain sorrel, hairy lousewort, purple saxifrage, and mountain avens. I was awash in a botanical sea, carried into an unexpected world.

Upon arising, he found none of the scents could be discerned more than a few inches above. He realized that the bird and her young would live among these scents:

A world of perfumes would cloak the hatchlings and saturate their feathers, becoming a sensory background to the birds' accumulating experience of living…

If "poets" who like to write free verse could write it like Dr. Glassley, I'd read more free verse.

Of oceans and crystals

kw: geology, earth, crystal chemistry

In a number of recent discussions some basic questions of Earth science have arisen. Putting together a number of ideas, I realized that on the grossest scale, the Earth consists of three oceans and five crystals.

From outermost inward:

• The first ocean is the atmosphere. This is of geophysical and biological interest, but air is not a "rock". However, atmospheric processes have a lot to do with the movement of mineral materials on and in the upper parts of the crust.
• The second ocean is "the Ocean", primarily the saltwater that covers 71% of the surface to an average depth of 4 km. Low-salinity and fresh waters make up a fraction of a percent, and ice constitutes more than half of that. When I lived in South Dakota, we thought of snow as a special kind of sand, and just drove on it. The interaction of the water ocean with oceanic crust produces continental crust.
• The first crystal is the continental crust. To a first approximation, it is composed of feldspar with impurities. It averages about 20 km thick, ranging up to 40 km or so beneath large mountain ranges. Why do I call it a crystal? Most of the "rock forming" minerals are actually a framework of oxygen ions held together with metal ions, chiefly silicon, aluminum, magnesium and iron. Due to the activity of water and living things on shallow minerals, there is also a considerable component of calcium oxide, AKA limestone. But this is also a framework of oxygen held together by calcium ions. This immense oxygen has a comparatively low density, around 2.6. It was distilled from the minerals in the next crystal by tectonic activity coupled with water's dissolving power.
• The second crystal is the oceanic crust. It is primarily a mixture of olivine and pyroxene, which are also oxygen frameworks held together by the same metallic ions, but in a denser configuration, with a density of around 3.2 to 3.4. The thickness of oceanic crust is about 8 km, but quite variable. It is formed by expulsion of mantle materials into the depths of the water ocean by tectonic activity.
• The next two crystals constitute the mantle. The upper mantle grades from primarily pyroxene to enstatite, as the pressure and temperature increase downward. The density of enstatite approaches 4. 
• The lower mantle is primarily magnesium silicate with the structure of Perovskite, and its density reaches 6 in the very deep mantle. This mineral is a close approximation to a close-packed structure. Think of cannon balls stacked in a 3-sided pyramid. This is "cubic closest packing" (CCP); the pyramid is a corner cut off a cube. Each ball is touching 12 others. In high-pressure Perovskite, each oxygen is touching eight other oxygens and four magnesium (or iron) ions, which at this pressure are similar in size to oxygen. Together they form a CCP network with the tiny silicon ions fitting into the spaces between.
• Next we have the third ocean, the outer core. This is generally considered a liquid, particularly because it will not transmit S-type seismic waves, only P-waves. However, it is a stiff liquid, and a chunk of it suddenly brought to the lab would sit there (burning a hole in even an asbestos bench) and flow even more slowly than cold molasses – although that might change very rapidly once the huge pressure is released. Nonetheless, its fluid motions are apparently what create the Earth's magnetic field. It is composed of iron and nickel, with up to 10% sulfur. Although it is less than a tenth of Earth's volume, with a density more than 10, it is more than a quarter of the mass of the planet.
• Finally, the fifth crystal is the inner core. Also composed of iron and nickel, it probably has much less of a sulfur constituent. It is crystalline, and measurements of its seismic anisotropy indicate it may indeed be a single huge (2,400 km diameter) metallic crystal. It is not known if its rotation rate exactly matches that of the rest of the Earth. Its density is about 15, and its temperature may exceed 6,000K, or 11,000°F. Subtracting the amount of heat we think is generated within the earth by radioactive elements (U, Th and K, mainly), it is thought that this central crystal is growing at a rate of a few cm per century.

To sum up simply: an ocean of air, an ocean of salty water, four crystals consisting of ever-denser packings of oxygen held by metal ions, an ocean of nickel-iron, and a metallic crystal.

When our global engine was fueled

kw: book reviews, nonfiction, geology, geological history, plate tectonics

When I was quite young, I was told that the Earth has mountains because the planet is still shrinking as it cools down internally. This had been the prevailing theory for about a century. Then in 1969 I changed my college major from Physics to Geology, and the University was just implementing a new curriculum based on plate tectonics as explained in the book The New View of the Earth: Moving Continents and Moving Oceans by Seiya Uyeda (the latest edition is 1978, but it was first translated and published in English in 1968).

This was a new understanding, that the crust of the Earth is composed of about a dozen stiff plates that grow by volcanic accretion (spreading) on some boundaries, grind against one another along others, and are consumed into the mantle or squeezed up into mountains at others. The most prominent and still rising mountain chain is the Himalayas, pushed up as the Indian plate jams northward into the Asian plate. The "grinding against" region of greatest familiarity to Americans is the San Andreas fault zone that runs from the Gulf of California between Baja and the rest of Mexico, northward through San Francisco and out to sea near there. Nearly all the spreading/accretion regions are beneath the sea, most notably the Atlantic, but Iceland is a portion of the mid-Atlantic Rise that emerges above sea level.

It is now thought that plate processes have proceeded for at least two or three billion years. In that time, the continents alternated between a scattered condition, even more scattered than today, and a merged condition where there was primarily one large supercontinent. The most recent merging produced a supercontinent we call Pangaea, for "all Earth". The rest of the planet was oceanic, and nearly all this global ocean was a single superocean we call Panthalassa, for "all sea". But Pangaea was C-shaped, and there were large islands that almost completed the outline of a circle closing the C, so this is considered a separate ocean has has been given the name Tethys, from the name of the wife of Oceanus, the original Greek sea god.

Tethys Ocean was first enclosed about 260 million years ago (mya), and grew in importance and size for 200 million years, then waned and was squeezed out of existence by about 6 mya. Among other things, this "temporary" ocean is responsible for the high-energy economy this generation enjoys. The growth, career and waning of Tethys is the subject of a remarkable book, Vanished Ocean: How Tethys Reshaped the World by Dorrik Stow.

Dr. Stow has done what I once hoped to do: become a globe-trotting professor of Geology. As I now judge things, I lack the strategic vision to synthesize the many threads of Earth science he has mastered and expressed in this book, so I have gratefully, and rather slowly, read through every bit. Of the many messages he brings, I'll briefly outline just one, the physiography of the continents at a few key epochs, and what that means to the modern economy. First, we will look at this figure from the book (p 24), including its caption.

The great continent that lies athwart the equator blocks an equatorial current that would otherwise run right around the planet. Whenever this has been the case, the Earth has had a period of global cooling with ice ages. Such is the condition today, with the North-South American landmass crossing the equator, and a significant secondary blockage by Africa. We are actually in the midst of an ice age that has lasted for two million years, with periodic interglacial warmings.

Between these two "icehouse condition" stages, the Earth's climate was much warmer. A circum-equatorial ocean current allows a much greater buildup and distribution of heat and a "greenhouse condition" to prevail. Tethys grew, broke through Pangaea as the supercontinent broke apart into Laurasia and Gondwana, and presided over more than 200 million years of greenhouse warming.

This growing ocean was ringed with areas of upwelling from deeper, nutrition-laden waters, wherever its currents impinged on the continental margins. Other areas of upwelling ringed the continents, until by the time tyrannosaurs were chasing Triceratops about, a very active period of organic accumulation on the ocean floors had been going on for 50-100 million years. The accumulation was facilitated by anoxic conditions in the deep ocean because of the very high surface growth of plankton. When lots of plankton die and rain down to the ocean floor under anoxic conditions, organic-rich sediments get laid down, and once they are buried and heated to about 100°C, they produce a lot of petroleum. Further heating cracks this to natural gas.

Thus, the height of the Tethys is marked by large accumulations of oil-producing sediments, which were overlaid by capping layers of clay and silt as Tethys began to be squeezed out of existence. The map below shows the major oil-bearing zones, and it is easy to see that about half of them are marginal to Tethys. As Tethys was squeezed by the later episode of continental convergence that led to today's configuration, these were concentrated into a belt that is centered on the Middle East, but also includes the Gulf of Mexico. Major secondary belts are the North Sea and offshore California-to-Alaska. The storage of all this oil was completed before 15 mya, and most of that much earlier.

Here we see the results of the second great energy-storing episode in Earth's history—the first was the laying down of great coal deposits 50-150 million years earlier, when terrestrial and swamp vegetation was buried in large amounts. The energy-rich economy we enjoy today is largely due to the growth and shrinkage of Tethys. The huge salt deposits in many of the oil provinces testify to the drying of the remnants of this great ocean, and incidentally provided trapping layers for the oil forming from its deeper sediments.

Today, the north-south axis of the Americas plus Africa is holding Earth in an icehouse condition, with periodic interglacial episodes. All of the history of civilization is a history of the latter two-thirds of the latest interglacial episode. We are possibly extending its duration by burning the legacy of millions of years of organic accumulation and releasing carbon dioxide to the atmosphere. In a few decades, the age of oil will be over. Will the human race then find itself using the fossil fuels that remain to stave off the cold of the next ice cycle? Icehouse conditions are expected to last a good while yet; Dr. Stow thinks even 50 million years into the future, and conjectures that a land connection between South America and Antarctica will have closed by then, further deepening the icehouse. Time will surely tell.

This is but one important story the author has to tell. He gives many details of the evidence he and others have gathered to piece together the story of how Pangaea was rearranged into a series of continents that coasted the great Tethys Ocean, then pressed it out of existence. The Mediterranean Sea is a re-emergence of a small portion of Tethys, and future oceans are being born as the Red Sea and the East African rift zones get organized as new spreading centers. They will probably become axial rifts of the next generation of oceans as the slow, persistent drama of plate tectonics continues.

One upon another

kw: science, geology, interpretation

I tend to have a messy desk. Things I don't deal with immediately get other stuff piled on top, until there are several layers. Then when I remember something I have to do something about, I need to think, "When was that?" Once I know that, I know how deep I have to dig to find it. I usually know approximately where to look. I also know that the older stuff is on the bottom.

Geology, the profession I was educated for, works in a reverse fashion. Most places, things are also in order, with the younger stuff on top or shallower than older stuff. Because most dirt, soil, and rock materials are laid down in order, and in layers, one of the first pieces of geological jargon a new geology student has to learn is "stratigraphy." The prefix "strat-" means "layer".

A short definition of stratigraphy is "The study and interpretation of layering in geological and archaeological deposits." Archaeology is just geology applied to layers that may contain fossils or artifacts or other human or hominid remains. More recent stuff, in other words. When archaeologists dig into cave deposits to recover bones and artifacts, they are very careful to record which layer in which each item was found; they keep good stratigraphic records. Similarly, when palaeontologists retrieve fossils or other traces of ancient living things, or other materials of interest such as mineral deposits, they must keep good stratigraphic records.

What is of interest to me today is the variety of sub-disciplines that make up the large field of stratigraphic interpretation. Four words are used to describe four different means of interpreting the layering found in Earth's crust, to derive the relative older-younger relationships:

1. Lithostratigraphy is the study of the sequence of rock types. It is well known that many geological processes take place over large areas. The filling in of an ocean basin may be a generally uniform process that covers hundreds of miles. Sand dune fields that accompany desert formation may also cover many miles. So if in one large outcrop you find the sequence (from bottom to top) rocky sand, shaly mud, fine sand, dune sand; then several miles away there is an outcrop with the same sequence and similar thicknesses of each layer, it is likely that the two outcrops are related. Both cover a similar time span, and a few events within that time span can be correlated between the two outcrops.
2. Biostratigraphy is the study of sequences of fossils, often within layers that are lithologically uniform, and of course from layer to layer. Many kinds of animals and some plants were widespread, even having worldwide distribution during the period in which they flourished. Whenever you find one of these "index fossils" as they are called, you can state that the layer in which it was found has a certain geological relationship, wherever on Earth it may be.
3. Stable Isotope Stratigraphy is not usually worldwide in scope, but serves to correlate things like a certain concentration of an isotope such as O18 throughout a region that experienced a similar climatic history, such as a large lake or a semi-enclosed ocean basin. Most frequently, it is the pattern in the rise and fall of the isotope's concentration that is mapped and used to correlate from place to place.
4. Magnetostratigraphy is the most recent stratigraphic tool, being only about fifty years old. It is based on the learning in the early 1960s that Earth's magnetic field has reversed itself periodically. By taking a series of magnetic measurements across a layered outcrop, the positions of reversals can be mapped and correlated from place to place. This was a worldwide phenomenon.

These four provide relative timing but not absolute timing. A rough measure of absolute timing can be determined by observing the rate at which certain kinds of sediments are laid down, particularly those that form yearly layers that can be distinguished in the rock. Varved shales are an example, and have been used to determine absolute times, in certain specific locations, for deposits as old as 400,000 years (but imagine counting all those thin layers!).

The absolute time scale needed to tie all of the stratigraphic data together was provided during the Twentieth Century by radiostratigraphy, which uses long-lived radioactive isotopes to age-date a number of common rock types. There are a number of different time ranges that are related to various radioisotopes. For example, the most common isotope of Uranium, U-238, is one of the longest, with a half life just over 4.5 billion (4500 million) years. Because of its feeble activity, it is not useful for "short" spans of time of less than a few million years. At the other end of the scale, the isotope C-14 has a half life of 5,730 years. While it is hard to determine very short time spans of a decade or less, it is well suited to time ranges between 100 and 75,000 years. Other isotopes can be used to cover intermediate spans of time.

One very useful synergy between methods is to gather well-dated specimens of index fossils. That way, for most uses, if you know that a certain fossil animal only lived between 105 and 108 million years ago, finding this fossil immediately places the rock you found it in within this time range. Finding multiple index fossils and gathering a suite of them across an outcrop gives you a series of good measures of the chronostratigraphy of the deposit, from which you can interpolate the points in between as needed.

The aim of stratigraphic study is to pin down the chronostratigraphy, by whatever method(s). Once a geologist knows that, a lot of other pieces of information can be correlated to develop a proper interpretation of the events that occurred to put those rocks in that place. The events are the goal; the rocks are the evidence.