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382ec23
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"Push up some mountains. Cut them down. Drown the land under the sea. Push up some more mountains. Cut them down. Push up a third set of mountains, and let the river cut through them. "Unconformity" is the geologic term for an old, eroded land surface buried under younger rock layers. Put your outspread hand over the Carlin Canyon, Nevada unconformity and your fingers span roughly forty million years- the time that it took to bevel down the first set of mountains and deposit the younger layers on top. What is forty million years? Enough time for a small predatory dinosaur to evolve into a bird. Enough time for a four-legged, deer-like mammal to evolve into a whale. And far more than enough time to turn an ape-like creature in eastern Africa into a big-brained biped who can marvel at such things. The Grand Canyon's Great Unconformity divides 1.7 billion-year-old rock from 550 million-year-old rock, a gap of more than one billion years. One billion years. I earn my salary studying the Earth and teaching its history, but I admit utter helplessness in comprehending such a span. A billion pages like those of this book would stack up more than forty miles. I had lived one bullion seconds a few days before my thirty-second birthday. A tape measure one billion inches long would stretch two-thirds of the way around the Earth. Such analogies hint at what deep time means- but they don't get us there. "The human mind may not have evolved enough to be able to comprehend deep time," John McPhee once observed, "it may only be able to measure it."
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evolution
nature
wonder
erosion
mountains
geology
mystery
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Keith Meldahl |
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ca4d30a
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The earth is a dynamic place [...] with multiple different processes of deposition and erosion under way at all times. You can make guesses based on style and weathering, but fragments of worked stone that have been in the open for an unknown period can't be dated by their archaeological context, because there is none. Carbon-dating organic materials in the sediment in which they were found won't work, either, because they were never entombed and preserved in sediment. And in fact no other objective and widely accepted method of dating can tell us how old they are. For these reasons archaeologists have to discount artifacts found on the surface when coming to any conclusions about the age of a site, even though the artifacts themselves may obviously be ancient.
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earth
deposition
dynamic
erosion
preservation
geology
dating
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Graham Hancock |