EDS -- EMBARGOED FOR RELEASE: 22 FEBRUARY 2001 AT 14:00 EST, 19:00 GMT 

February 20, 2001. Copyright 2001. Graphic News. All rights reserved.

ÒBUCKYBALLSÓ FROM SPACE GIVE CLUE TO MASS EXTINCTION 250 MILLION YEARS AGO

LONDON, February 20, Graphic News: EARTHÕS most severe mass extinction -- an event 250 million years ago that wiped out 90 percent of all marine species and 70 percent of land vertebrates -- was triggered by a collision with a comet or asteroid, according to new findings by a team led by a University of Washington scientist. 

The collision wasnÕt directly responsible for the extinction but rather triggered a series of events, such as massive volcanism and changes in ocean oxygen, sea level and climate. Those in turn led to species extinction on a wholesale level, said Luann Becker, assistant professor of Earth and Space Sciences.

ÒIf the species cannot adjust, they perish. ItÕs a survival-of-the-fittest sort of thing,Ó Becker said. ÒTo knock out 90 percent of organisms, youÕve got to attack them on more than one front.Ó 

Becker, with colleagues from the University of Rochester; NASAÕs Ames Research Center; New York University and the Goddard Institute of Space Sciences, present their findings in the February 23 edition of the journal Science. 

The scientists do not know the site of the impact 250 million years ago, when all EarthÕs land formed a supercontinent called Pangaea. However, the space body left a calling card -- a much higher level of complex carbon molecules called buckminsterfullerenes, or buckyballs, with the noble (or chemically nonreactive) gases helium and argon trapped inside their cage structures. 

Fullerenes, which contain at least 60 carbon atoms and have a structure resembling a soccer ball or a geodesic dome, are named after Buckminster Fuller, who invented the geodesic dome. 

The researchers know these particular buckyballs are extraterrestrial because the noble gases trapped inside have an unusual ratio of isotopes. For instance, terrestrial helium is mostly helium-4 and contains only a small amount of helium-3, while extraterrestrial helium -- the kind found in these fullerenes -- is mostly helium-3. 

ÒThese things form in carbon stars. ThatÕs whatÕs exciting about finding fullerenes as a tracer,Ó Becker said. The extreme temperatures and gas pressures in carbon stars are perhaps the only way extraterrestrial noble gases could be forced inside a fullerene, she said. These gas-laden fullerenes were formed outside the Solar System, and their concentration at this period of prehistoric mass extinction, known as the Permian-Triassic boundary, means they had to be delivered by a comet or an asteroid. 

The researchers estimate the comet or asteroid was 6 to 12 kilometers (4 to 7.5 miles) across, about the size of the asteroid that left the huge Chicxulub crater on MexicoÕs Yucatan Peninsula 65 million years ago. That impact is believed responsible for the extinction of the dinosaurs. 

The telltale fullerenes containing helium and argon were extracted from sites in Japan, China and Hungary, where the sedimentary layer at the boundary between the Permian and Triassic periods has been exposed.

Scientists have long known of the mass extinction 250 million years ago, since many fossils below the boundary -- such as trilobites, which once numbered more than 15,000 species -- diminish sharply close to the boundary and are not found above it. There also is strong evidence suggesting the extinction happened very rapidly, in as few as 8,000 to 100,000 years, which the latest research supports. ÒThatÕs a microsecond in geologic time,Ó Becker said.
/ENDS
Sources: Science, NASA