Dinosaur die out might have been second of two closely timed extinctions

The most-studied mass extinction in Earth history happened 65 million years ago and is widely thought to have wiped out the dinosaurs. New University of Washington research indicates that a separate extinction came shortly before that, triggered by volcanic eruptions that warmed the planet and killed life on the ocean floor.

The well-known second event is believed to have been triggered by an asteroid at least 6 miles in diameter slamming into Mexico's Yucatán Peninsula. But new evidence shows that by the time of the asteroid impact, life on the seafloor -- mostly species of clams and snails -- was already perishing because of the effects of huge volcanic eruptions on the Deccan Plateau in what is now India.

"The eruptions started 300,000 to 200,000 years before the impact, and they may have lasted 100,000 years," said Thomas Tobin, a UW doctoral student in Earth and space sciences.

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