About 250 million years ago, life went into shock. Set in motion by forces of geology and climate, a great wave of extinction wiped out well over 70 percent of all species on Earth.
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The lifeforms that repopulated the planet were tough. Hardy filter feeding species carpeted the marine realm. Fungi and shrubs covered the land. An army of mammal-like reptiles dominated vertebrate life. The bleak landscape, what some paleontologists call a dead zone, persisted for well over 3 million years.