A short history of nearly everything - Bill Bryson [274]
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*27It is KT rather than CT because C had already been appropriated for Cambrian. Depending on which source you credit, the K comes either from the Greek kreta or German Kreide. Both conveniently mean “chalk,” which is also what Cretaceous means.
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*28For those who crave a more detailed picture of the Earth's interior, here are the dimensions of the various layers, using average figures: From 0 to 40 km (25 mi) is the crust. From 40 to 400 km (25 to 250 mi) is the upper mantle. From 400 to 650 km (250 to 400 mi) is a transition zone between the upper and lower mantle. From 650 to 2,700 km (400 to 1,700 mi) is the lower mantle. From 2,700 to 2,890 km (1,700 to 1,900 mi) is the “D” layer. From 2,890 to 5,150 km (1,900 to 3,200 mi) is the outer core, and from 5,150 to 6,378 km (3,200 to 3,967 mi) is the inner core.
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*29The discovery of extremophiles in the boiling mudpots of Yellowstone and similar organisms found elsewhere made scientists realize that actually life of a type could range much farther than that—even, perhaps, beneath the icy skin of Pluto. What we are talking about here are the conditions that would produce reasonably complex surface creatures.
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*30Of the remaining four, three are nitrogen and the remaining atom is divided among all the other elements.
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*31Oxygen itself is not combustible; it merely facilitates the combustion of other things. This is just as well, for if oxygen were combustible, each time you lit a match all the air around you would burst into flame. Hydrogen gas, on the other hand, is extremely combustible, as the dirigible Hindenburg demonstrated on May 6, 1937, in Lakehurst, New Jersey, when its hydrogen fuel burst explosively into flame, killing thirty-six people.
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*32If you have ever been struck by how beautifully crisp and well defined the edges of cumulus clouds tend to be, while other clouds are more blurry, the explanation is that in a cumulus cloud there is a pronounced boundary between the moist interior of the cloud and the dry air beyond it. Any water molecule that strays beyond the edge of the cloud is immediately zapped by the dry air beyond, allowing the cloud to keep its fine edge. Much higher cirrus clouds are composed of ice, and the zone between the edge of the cloud and the air beyond is not so clearly delineated, which is why they tend to be blurry at the edges.
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*33The term means a number of things to different people, it appears. In November 2002, Carl Wunsch of MIT published a report in Science, “What Is the Thermohaline Circulation?,” in which he noted that the expression has been used in leading journals to signify at least seven different phenomena (circulation at the abyssal level, circulation driven by differences in density or buoyancy, “meridional overturning circulation of mass,” and so on)—though all have to do with ocean circulations and the transfer of heat, the cautiously vague and embracing sense in which I have employed it here.
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*34The indigestible parts of giant squid, in particular their beaks, accumulate in sperm whales' stomachs into the substance known as ambergris, which is used as a fixative in perfumes. The next time you spray on Chanel No. 5 (assuming you do), you may wish to reflect that you are dousing yourself in distillate of unseen sea monster.
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*35There are actually twenty-two naturally occurring amino acids known on Earth, and more may await discovery, but only twenty of them are necessary to produce us and most other living things. The twenty-second, called pyrrolysine,