10 lines
908 B
TeX
10 lines
908 B
TeX
\section{The Cambrian Explosion}
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\lettrine[lraise=0.1]{A}{bout} 540 million years ago, after roughly 3 billion years of almost exclusively microbial life, the fossil record shows an extraordinary proliferation of complex animal body structures appearing in geologically very rapid time --- perhaps 20 million years, a geological blink of an eye.
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It's known as the Cambrian Explosion.
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Virtually every major animal body plan alive today --- left-and-right symmetry, eyes, appendages, nervous systems --- appears in this window. Before it: microbial mats and simple soft-bodied organisms. After it: the full complexity of animal life.
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The trigger is still debated --- rising oxygen levels, ecological feedback loops, genetic innovations, possibly all three. But the threshold is unmistakable: something altered the equilibrium sufficiently that an entirely new order of organism complexity became possible.
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