Asteroid or comet may have caused 'mother of all extinctions'

WASHINGTON -- Some 250 million years ago, almost 90 percent of life on Earth died in history's most devastating extinction. A new study suggests it was triggered by an asteroid or comet like the one that much later killed the dinosaurs.

In a study appearing Friday in the journal Science, researchers say ancient deposits in China and Japan show chemical evidence that a space rock, 3 miles to 7 miles across, smashed to Earth during the time of the Permian-Triassic extinction.

In what has been called "the great dying," 90 percent of all ocean species and 70 percent of all land species vanished. It is a key event in the history of life on Earth.

"This was the mother of all extinctions," said Luann Becker, a University of Washington geochemist and lead author of the study.

The extinction occurred within 8,000 to 100,000 years -- "a microsecond in geologic time," Becker said. The Earth is thought to be 4.6 billion years old.

Large rocks from space smashing to Earth can set off an immense wave of superheated vapor that rolls for hundreds of miles and kills everything in its path. Impacts also can cause tidal waves in the ocean and send millions of tons of dust and vapor into the atmosphere, darkening the sun for months and chilling the Earth.

The extinction marked the end of the Permian geological period and was followed by the rise of the dinosaurs during the Triassic period.