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More than 250 million year's ago, something--until now, no one knew what--wiped out more than 70 percent of Earth's land dwellers and 90 percent of its ocean species. This included trilobites, soft-shelled sea creatures that crawled on the ocean floor--perhaps the most populous species of the time. Earth's worst mass extinction was so catastrophic it's dubbed "the Great Dying."

For years scientists have puzzled over the disaster's cause. Many suspected a high-speed comet or asteroid collision with Earth as the culprit. But unlike the space object that probably annihilated dinos 65 million years ago--and left a huge crater hidden beneath the Gulf of Mexico--there was no evidence to support the theory for the earlier extinction. That is, until University (if Washington researcher Luann Becker found the "smoking gun."

Last February, Becker and her team announced evidence linking a giant asteroid or comet to the extinction. Embedded in 250-million-year-old rock samples found in China and Japan are soccer ball-shaped molecules called buckyballs (named after scientist Buckminister Fuller, who discovered them). Trapped inside the molecules are vital clues to the mystery: two extraterrestrial gases, rare forms of helium and argon.

What do buckyballs and trapped gas have to do with asteroids and mass extinction? "We know these structures were formed outside our solar system," Becker says. "The extreme temperature and pressure needed to forge these gases don't exist on Earth."

The buckyball gases also match those found in meteorite samples, as well as gases found in deep soil layers linked to periods of extinction.

Far from gloom and doom, Becker believes comet collisions with Earth lend a helping hand to evolution, the process by which living things adapt to their environment. "It's as if life learns a lesson from what happened and comes back much more prepared to handle extreme conditions," she says.

Cretaceous-Tertiary (dinosaurs) 65
End Triassic 199 to 214
Permian-Triassic (the Great Dying) 251
Late Devonian 364
Ordovician-Silurian 439

Source: Smithsonian Institution's National Museum of Natural History
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Title Annotation:cause of the Great Dying
Publication:Science World
Geographic Code:1USA
Date:Apr 9, 2001
Previous Article:Short Takes.

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