New Approach to Explaining Evolution's Big Bang - NYTimes.com - 0 views
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the first animals evolved about 750 million years ago.
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But it’s not until around 520 million years ago that many major groups of living animals left behind their first fossils.
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For decades, scientists have searched for the trigger that set in motion this riot of diversity in the animal kingdom.
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“It became apparent just how many hypotheses there were out there,” Dr. Harper said. “Thirty-plus over the past 10 years.”
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it’s a mistake to search for a single cause. They propose that a tangled web of factors and feedbacks were responsible for evolution’s big bang.
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Long before the Cambrian explosion, Dr. Smith and Dr. Harper argue, one lineage of animals had already evolved the genetic capacity for spectacular diversity. Known as the bilaterians, they probably looked at first like little crawling worms.
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They offered evidence that the Cambrian Explosion was preceded by a rise in sea level that submerged vast swaths of land, eroding the drowned rocks.
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“There’s a big kick that correlates with the sea level rise,” Dr. Smith said of the fossil record. He and Dr. Harper propose that this kick happened thanks to the new habitats created by the sea level rise. These shallow coastal habitats were bathed in sunlight and nourished with eroding nutrients like phosphates. Animals colonized these new fertile habitats, Dr. Smith and Dr. Harper argue, and evolved to take up new ecological niches.
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The erosion of the coastlines released calcium, which can be toxic to cells. In order to survive, animals had to evolve ways to rid themselves of the poison. One solution may have been to pack the calcium into crystals, which eventually evolved into shells, bones, and other hard tissues.
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These shells and other hard tissues sped up animal evolution even more. Predators could grow hard claws and jaws for killing prey, and their prey could evolve hard shells and spines to defend themselves. Animals became locked in an evolutionary arms race.