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Meteor Linked to Global Extinction Eons Before Death of Last Dinosaurs

By Kenneth Chang

The New York Times -- About three dozen microscopic shards of rock unearthed in Antarctica may be the fragments of a meteor that killed most of life on earth 250 million years ago, scientists are reporting Friday.

The shards bolster theories that meteors caused several of the mass extinctions in earth’s history when large numbers of species died out almost simultaneously. Most scientists agree that the most recent major mass extinction 65 million years ago, which killed off the dinosaurs, was caused when a meteor struck the earth near the Yucatan Peninsula of Mexico.

The extinction 250 million years ago, known as the Permian-Triassic boundary, was the largest extinction of all. More than 90 percent of species living in the oceans and 70 percent of those on land disappeared.

At present, the primary suspected cause for the Permian-Triassic extinction is giant volcanic eruptions in Siberia, which might have induced catastrophic ecological changes.

Writing in today’s issue of the journal Science, the researchers report that they found the meteorite fragments in rocks in Antarctica that date to the Permian-Triassic boundary. The mineral composition of the fragments, each less than one-500,000th of an inch wide, correspond to that of certain meteorites and is like nothing found naturally on earth, they reported.

In addition, the scientists said, the same rocks had previously yielded soccer-ball-shaped molecules known as buckyballs containing extraterrestrial gases as well as grains of quartz with fractures that indicate they had been hit with a tremendous shock.

“Clearly, this evidence points toward a major impact at the Permian-Triassic boundary,” said Asish R. Basu, a professor of earth and environmental sciences at the University of Rochester and lead author of the Science paper. That, he said, is “the most reasonable interpretation.”

Luann Becker of the University of California at Santa Barbara and Robert J. Poreda of Rochester, who reported the buckyball evidence in 2001, are also authors of the new Science paper.

“I think this evidence bodes well for the impact theory,” Becker said in an e-mail message.

The same researchers will report at a American Geological Union meeting next week in San Francisco that they have also found tiny metal spheres they believe were part of the Earth’s crust and melted by the impact.

Others are not yet convinced. Eldridge Moores, an emeritus professor of geology at the University of California at Davis, described the meteorite fragments as “the most interesting evidence for a meteorite event at this boundary that I’ve seen so far.”