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.
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.