August 27, 2008 4:08 PM

Scientists close in on mass killer of life on earth

Scientific sleuths think they're making progress toward pinning down what caused the extinction of most plants and animals on Earth some 251 million years ago. The perpetrator wasn't an asteroid or comet, like the impact that wiped out the dinosaurs 65 million years ago, but a cascade of events that began with a monstrous outpouring of hot, reeking lava in Siberia that released massive amounts of carbon dioxide.

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