Geologic Time Scale

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  • Because the British were the most active in the early years of the discipline, British names are predominant in the geological lexicon.-A Short History by Bryson.

    • Devonian is of course from the English county of Devon.

    • Cambrian comes from the Roman name for Wales.

    • Ordovician and Silurian recall ancient Welsh tribes, the Ordovices and Silures.

    • Jurassic refers to the Jura Mountains on the border of France and Switzerland.

    • Permian recalls the former Russian province of Perm in the Ural Mountains.

    • Cretaceous (from the Latin for chalk) we are indebted to a Belgian geologist with the perky name of J. J. d’Omalius d’Halloy.

  • Geological time is divided first into four great chunks known as eras:-A Short History by Bryson.

    • Precambrian, Palaeozoic (from the Greek meaning “old life”), Mesozoic (“middle life”), Cenozoic (“recent life”).

    • These four eras are further divided into anywhere from a dozen to twenty subgroups, usually called periods or systems (Cretaceous, Jurassic, etc), then Lyell’s epochs—the Pleistocene, Miocene, etc—which apply only to the most recent (but paleontologically busy) 65 million years; and finally a mass of finer subdivisions known as stages or ages. Most of these are named, nearly always awkwardly, after places: Illinoian, Desmoinesian, Croixian, Kimmeridgian, etc.

Earth’s Composition

  • 1906: Irish geologist R. D. Oldham, while examining some seismograph readings from an earthquake in Guatemala, noticed that certain shock waves had penetrated to a point deep within the Earth and then bounced off at an angle, as if they had encountered some kind of barrier. From this he deduced that the Earth has a core.-A Short History by Bryson.

  • 1936: Danish scientist Inge Lehmann, studying seismographs of earthquakes in New Zealand, discover that there were two cores—an inner one, which we now believe to be solid, and an outer one (the one that Oldham had detected), which is thought to be liquid and the seat of magnetism.-A Short History by Bryson.

  • 1939: Three years later, a Croatian seismologist named Andrija Mohorovičić was studying graphs from an earthquake in Zagreb when he noticed a similar odd deflection, but at a shallower level. He had discovered the boundary between the crust and the layer immediately below, the mantle; this zone has been known ever since as the Mohorovičić discontinuity, or Moho for short.-A Short History by Bryson.

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  • From 0 to 40 kilometres is the crust. From 40 to 400 kilometres is the upper mantle. From 400 to 650 kilometres is a transition zone between the upper and lower mantle. From 650 to 2,700 kilometres is the lower mantle. From 2,700 to 2,890 kilometres is the “D” layer. From 2,890 to 5,150 kilometres is the outer core, and from 5,150 to 6,370 kilometres is the inner core.- A Short History by Bryson.

  • Earth Layers

    • 0 to 40km: Crust.

    • 40 to 400km: Upper Mantle

    • 400-650km: Trasition Zone between the Upper and Lower Mantle

    • 650-2700km: Lower Mantle

    • 2700-2890km: “D” Layer

    • 2890-5150km: Outer Core

    • 5150-6370km: Inner Core.

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  • Geothermal Gradient ~20-40 C/km.

  • When you to 100 to 130 feet below the surface, the temperature rises to 52 to 54 degrees, and it increases by 5.5 degrees every 300 or so feet as you continue to descend.-Secret Wisdom of Nature by Wohlleben.

Plate Tectonics

  • It is generally agreed that Plate Tectonics likely began about 3 billion years ago, during the Archean.

  • 1908 by an amateur American geologist named Frank Bursley Taylor. In Germany, however, Taylor’s idea was picked up, and effectively appropriated, by a theorist named Alfred Wegener, a meteorologist at the University of Marburg.

  • Wegener developed the theory that the world’s continents had once existed as a single landmass he called Pangaea, where flora and fauna had been able to mingle, before splitting apart and floating off to their present positions. He set the idea out in a book called Die Entstehung der Kontinente und Ozeane, or The Origin of Continents and Oceans, which was published in German in 1912.-A Short History by Bryson.

  • Holmes was the first scientist to understand that radioactive warming could produce convection currents within the Earth. In theory, these could be powerful enough to slide continents around on the surface. In his popular and influential textbook Principles of Physical Geology, first published in 1944, Holmes laid out a continental drift theory that was, in its fundamentals, the theory that prevails today.-A Short History by Bryson.

  • Africa today is pulling away from the Middle East at the rate of about one centimeter per year.-The Rise and Fall of the Dinosaurs by Brusatte.

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Ice Ages

  • We have had at least seventeen severe glacial episodes in the last 2.5 million years or so—the period that coincides with the rise of Homo erectus in Africa followed by modern humans. Two commonly cited culprits for the present epoch are:-A Short History by Bryson.

    • The rise of the Himalayas disrupting air flows. India, once an island, has pushed 2,000 kilometres into the Asian land mass over the past 45 million years, raising not only the Himalayas, but also the vast Tibetan plateau behind it. The hypothesis is that the higher landscape was not only cooler, but diverted winds in a way that made them flow north and towards North America, making it more susceptible to long-term chills.

    • The formation of the Isthmus of Panama disrupting ocean currents. Beginning about 5 mya, Panama rose from the sea, closing the gap between North and South America, disrupting the flows of warming currents between the Pacific and the Atlantic, and changing patterns of precipitation across at least half the world. One consequence was a drying out of Africa, which caused apes to climb down out of trees and go looking for a new way of living on the emerging savannas.

  • It is now generally believed that ice ages are initiated by small changes in the earth’s orbit, caused by, among other things, the gravitational tug of Jupiter and Saturn.-The Sixth Extinction by Kolbert.

Rocks and Minerals

  • Diamonds

    • What happens is that deep in the Earth there is an explosion that fires, in effect, a cannonball of magma to the surface at supersonic speeds. It is a totally random event. A kimberlite pipe could explode in your back garden as you read this. Because they come up from such depths—up to 200 kilometres down—kimberlite pipes bring up all kinds of things not normally found on or near the surface: a rock called peridotite, crystals of olivine and—just occasionally, in about one pipe in a hundred—diamonds. Lots of carbon comes up with kimberlite ejecta, but most is vaporized or turns to graphite. Only occasionally does a hunk of it shoot up at just the right speed and cool down with the necessary swiftness to become a diamond.-A Short History by Bryson.

    • Huge trees topple over and sink into the quagmire, where a lack of O impedes rotting. More and more dead vegetation builds up until a thick layer of sodden plant matter is in place. Rivers then wash sand and silt into the swamp, which compresses the vegetation, driving out moisture and other impurities. As the swamp is buried deeper and deeper in the Earth, heat and time alter the chemistry of the wood, leaves, and other organic matter. First, the peat is converted to brown coal, and, after many millions of years, the brown coal becomes bituminous coal. If further pressure and heat are applied, and more impurities removed, it can finally become anthracite, and at its most exquisite anthracite- in the form of jet- is a beautifully jewel, as pure a C treat as a diamond.-The Weather Makers by Flannery. 


  • Oil is the product of life in ancient oceans and estuaries. It is composed primarily of the remains of plankton- in particular, single celled plants known as phytoplankton. Most of the world's oil reserves are thought to have originated from deep, still, O-poor ocean basins in areas where upwelling bring cold, nutrient-rich bottom-waters to the sunlit surface. In such conditions, the nutrients supercharge the phytoplankton so that they bloom in enormous quantity; when they die, their remains are carried down to O-free depths, where their Organic matter can accumulate without being consumed by bacteria. The geological process for making oil. First the sediments containing the phytoplankton must be buried and compressed by other rocks. Then, the absolute right conditions are needed to squeeze the organic matter out of the source rocks and to transfer it, through cracks and crevices, into a suitable storage stratum. This stratum must be porous, but above it must lie a layer of fine-grained, impervious rock, strong enough to withstand the pressures that shot the oil and gas high into the air above Spindletop and thick enough to forbid escape. In addition, the waxes and fats that are the source of oil need to be "cooked" at 212-275F for millions of years. IF the temperature ever exceeds these limits, all that will result is gas, or else the hydrocarbons will be lost entirely.-The Weather Makers by Flannery.




  • 1650: Archbishop James Ussher of the Church of Ireland made a careful study of the Bible and other historical sources and concluded, in a hefty tome called Annals of the Old Testament, that the Earth had been created at midday on 23 October 4004 BC.-A Short History by Bryson.

  • Hutton noticed that if he used a pencil to connect points of equal height, it all became much more orderly. Indeed, one could instantly get a sense of the overall shape and slope of the mountain. He had invented contour lines.-A Short History by Bryson.

  • Eventually in this process all the tiny organisms die and drift to the bottom of the sea, where they are slowly compressed into limestone. Among the tiny atomic structures the plankton take to the grave with them are two very stable isotopes—oxygen-16 and oxygen-18. (If you have forgotten what an isotope is, it doesn’t matter, though for the record it’s an atom with an abnormal number of neutrons.) This is where the geochemists come in, for the isotopes accumulate at different rates depending on how much oxygen or carbon dioxide is in the atmosphere at the time of their creation. By comparing the ancient rates of deposition of the two isotopes, geochemists can read conditions in the ancient world—oxygen levels, air and ocean temperatures, the extent and timing of ice ages and much else. By combining their isotope findings with other fossil residues that indicate other conditions such as pollen levels and so on—scientists can, with considerable confidence, recreate entire landscapes that no human eye ever saw.-A Short History by Bryson.

  • According to Lyell, every feature of the landscape was the result of very gradual processes operating over countless millennia—processes like sedimentation, erosion, and volcanism, which were all still readily observable. Lyell’s thesis would be summed up as “The present is the key to the past.”-The Sixth Extinction by Kolbert.

  • Darwin had been invited to serve as a sort of gentleman’s companion to the captain of the HMS Beagle, Robert FitzRoy. The ship was headed to South America to survey the coast and resolve various mapping discrepancies that hindered navigation. (The Admiralty was particularly interested in finding the best approach to the Falkland Islands, which the British had recently assumed control of.) The voyage, which would last until Darwin was twenty-seven, would take him from Plymouth to Montevideo, through the Strait of Magellan, up to the Galápagos Islands, across the South Pacific to Tahiti, on to New Zealand, Australia, and Tasmania, across the Indian Ocean to Mauritius, around the Cape of Good Hope, and back again to South America.-The Sixth Extinction by Kolbert.

  • The more Darwin explored the world, the more Lyellian it seemed to him to be.-The Sixth Extinction by Kolbert.

  • Toward the end of the Beagle’s voyage, Darwin encountered coral reefs. These provided him with his first major breakthrough, a startling idea that would ease his entrée into London’s scientific circles. Darwin saw that the key to understanding coral reefs was the interplay between biology and geology. If a reef formed around an island or along a continental margin that was slowly sinking, the corals, by growing slowly upward, could maintain their position relative to the water. Gradually, as the land subsided, the corals would form a barrier reef. If, eventually, the land sank away entirely, the reef would form an atoll.-The Sixth Extinction by Kolbert.

  • “Without Lyell there would have been no Darwin.”-The Sixth Extinction by Kolbert.

  • Darwin recognized that just as the features of the inorganic world—deltas, river valleys, mountain chains—were brought into being by gradual change, the organic world similarly was subject to constant flux. Ichthyosaurs and plesiosaurs, birds and fish and—most discomfiting of all—humans had come into being through a process of transformation that took place over countless generations. This process, though imperceptibly slow, was, according to Darwin, still very much going on; in biology, as in geology, the present was the key to the past. In one of the most often-quoted passages of On the Origin of Species, Darwin wrote: 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.-The Sixth Extinction by Kolbert.

  • Diminishing population density may have made survival less likely for the remaining individuals, a phenomenon that’s known as the Allee effect.-The Sixth Extinction by Kolbert.

  • At the heart of Darwin’s theory, as one of his biographers has put it, is “the denial of humanity’s special status.” And what was true of evolution should also hold for extinction, since according to Darwin, the latter was merely a side effect of the former. Species were annihilated, just as they were created, by “slow-acting and still existing causes,” which is to say, through competition and natural selection; to invoke any other mechanism was nothing more than mystification.-The Sixth Extinction by Kolbert.



  • In the 1960’s, British atmospheric scientist, chemist, and marine biologist James Lovelock proposed his Gaia hypothesis, which describes the Earth as behaving like a super-organism, its soil, atmosphere, and oceans composing  circulatory system regulated by its resident flora and fauna.-The World Without us by Weisman.


  • Arthur Holmes, who devised a method for accurately dating rocks based on the decay rate of uranium into lead, allowing him to show that Earth was at least three billion years old.-A Short History by Bryson.

  • 1896 when Henri Becquerel in Paris carelessly left a packet of uranium salts on a wrapped photographic plate in a drawer. When he took the plate out some time later, he was surprised to discover that the salts had burned an impression in it, just as if the plate had been exposed to light.-A Short History by Bryson.

  • the rocks were converting mass into energy in an exceedingly efficient way. Marie Curie dubbed the effect “radioactivity.”-A Short History by Bryson.

Ice Core Dating

  • It occurred to him that ice cores could provide the answer. It was known that snowfall in places like Greenland accumulates into discrete annual layers (because seasonal temperature differences produce slight changes in coloration from winter to summer). By counting back through these layers and measuring the amount of lead in each, he could work out global atmospheric lead concentrations at any time for hundreds, or even thousands, of years. The notion became the foundation of ice core studies, on which much modern climatological work is based.-A Short History by Bryson.

  • Isotope geochemistry. The long-ago seas of the Carboniferous and Devonian swarmed with tiny plankton which wrapped themselves inside tiny protective shells. Then, as now, the plankton created their shells by drawing oxygen from the atmosphere and combining it with other elements (carbon especially) to form durable compounds such as calcium carbonate. It’s the same chemical trick that goes on in (and is discussed elsewhere in relation to) the long-term carbon cycle—a process that doesn’t make for terribly exciting narrative but is vital for creating a habitable planet.–A Short History by Bryson.


Carbon Dating

  • Willard Libby was in the process of inventing radiocarbon dating.–A Short History by Bryson.

  • Based on the realization that all living things have within them an isotope of carbon called carbon-14, which begins to decay at a measurable rate the instant they die. Carbon-14 has a half-life—that is, the time it takes for half of any sample to disappear—of about 5,600 years, so by working out how much of a given sample of carbon had decayed, Libby could get a good fix on the age of an object—though only up to a point. After eight half-lives, only 0.39 per cent of the original radioactive carbon remains, which is too little to make a reliable measurement, so radiocarbon dating works only for objects up to forty thousand or so years old.–A Short History by Bryson.

  • The volume of atmospheric carbon-14 varies depending on how well or not the Earth’s magnetism is deflecting cosmic rays. The decay constant, was out by about 3 per cent.–A Short History by Bryson.


  • An erupting volcano releases lava, ash, and pyroclastic flows (aka Nuee Ardante)- clouds of burning gas and ash that advance at high speed and destroy everything in their path.

  • As Volcanic material weathers, it matures into rich soils.

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  • NASA decided to test some new high-altitude cameras by taking photographs of Yellowstone, copies of which a thoughtful official passed on to the park authorities on the assumption that they might make a nice display for one of the visitor centres. As soon as Christiansen saw the photos he realized why he had failed to spot the caldera: virtually the whole park—9,000 square kilometres—was caldera. The explosion had left a crater nearly 65 kilometres across. Yellowstone, it turns out, is a supervolcano. It sits on top of an enormous hot spot, a reservoir of molten rock that begins at least 200 kilometres down in the Earth and rises to near the surface, forming what is known as a superplume. The heat from the hot spot is what powers all of Yellowstone’s vents, geysers, hot springs and popping mud pots. Beneath the surface is a magma chamber that is about 72 kilometres across—roughly the same dimensions as the park—and about 13 kilometres thick at its thickest point.-A Short History by Bryson.

  • The Palisades is what geologists refer to as a sill—an intrusion of magma that pokes its way in between two layers of rock far underground, but then hardens into stone before it can erupt as lava.-The Rise and Fall of the Dinosaurs by Brusatte.

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Earthquakes: (

  • Nine million years ago, the Tetons didn’t exist. The land around Jackson Hole was just a high grassy plain. But then a 64-kilometre-long fault opened within the Earth and since then, about once every nine hundred years, the Tetons experience a really big earthquake, enough to jerk them another 2m higher. It is these repeated jerks over aeons that have raised them to their present majestic heights of 2,000m.-A Short History by Bryson.

  • Hypocenter: Earthquake Point of Origin

  • Epicenter: Earthquake Point of Origin on the Earth’s Surface.

  • Shallow Earthquake: <44miles below surface.

  • Intermediate Earthquake: 44-186miles below surface.

  • Deep Earthquake: >186miles below surface.


  • Orogenesis: The process of mountain building.

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Amazon Rainforest

  • Transpiration of water vapor from plants is the chief source of rainfall in the Amazon.-The Weather Makers by Flannery.

  • Few conventional annual crops grow in the Amazon's aluminum saturated soil.-1493 by Mann.

  • The curupira has a boyish face, copious hair, and backward-pointing feet. He preys on poachers and anyone else who takes too much from the forest.-The Sixth Extinction by Kolbert.

  • A theory of why the tropics are so diverse is that greater competition has pushed species to become more specialized, and more specialists can coexist in the same amount of space.-The Sixth Extinction by Kolbert.


  • Permafrost: Ground remains frozen throughout the year. Forms a layer up to 600m thick in parts of Alaska and more than 1000m thick in parts of Siberia where the ground has still not thawed from the last ice age.


  • Sahel: Semi-Arid Transitional belt that separates the desert from central Africa's tropical savanna. The sahel is six hundred miles thick at its widest point.-Countdown by Weisman.

  • Desert: receives less than 10" of rainfall annually.



  • Grasslands can grow where the climate is too dry for threes.

  • Generally located in the interior of continents.

  • AKA Prairie (French for meadow) aka Steppe aka Llanos in Central America aka Savannah in Africa.

  • Everglades is a flooded Grassland.

Temperate Forests

  • Temperate Forests: Lies between the tropics and the Arctic and Antarctic Circles.

    • Climate is Highly Seasonal and seasons are defined mainly by temperature.

    • Broad Leaved Deciduous Trees make up Boreal (means “Northern”) Forests.

Conifer Forests

Tropical Forests

  • Tropical Forests: Grow in Equatorial Lowlands where the climate is permanentiyl wet and the difference in temperature between day and night is greater than that between summer and winter.

    • Dominated by borad-leaved evergreen trees at least 30m tall and thick,.

Polar Regions: The Earth North or South of 66.5d where there is a period in midwinter when the Sun never rises above the horizon.