Thread: Antarctic crater linked to ancient die-off

Scientists say impact might have caused extinction 250 million years ago

http://www.msnbc.msn.com/id/13089686/

By Robert Roy Britt
Senior science writer

Updated: 8:06 p.m. ET June 1, 2006
An apparent crater as big as Ohio has been found in Antarctica. Scientists think it was carved by a space rock that caused the greatest mass extinction on Earth, 250 million years ago.

The crater, buried beneath a half-mile (1 kilometer) of ice and discovered by some serious airborne and satellite sleuthing, is more than twice as big as the one involved in the demise of the dinosaurs.

The crater's location, in the Wilkes Land region of East Antarctica, south of Australia, suggests it might have instigated the breakup of the so-called Gondwana supercontinent, which pushed Australia northward, the researchers said.

"This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," said Ralph von Frese, a professor of geological sciences at Ohio State University.

The crater is about 300 miles (500 kilometers) wide. It was found by looking at differences in density that show up in gravity measurements taken with NASA's GRACE satellites. Researchers spotted a mass concentration, which they call a mascon — dense stuff that welled up from the mantle, likely in an impact.

"If I saw this same mascon signal on the moon, I'd expect to see a crater around it," Frese said. (The moon, with no atmosphere, retains a record of ancient impacts in the visible craters there.)

So Frese and colleagues overlaid data from airborne radar images that showed a 300-mile-wide subsurface, circular ridge. The mascon fit neatly inside the circle.

"And when we looked at the ice-probing airborne radar, there it was," he said Thursday.

The Permian-Triassic extinction, as it is known, wiped out most life on land and in the oceans. Researchers have long suspected a space rock might have been involved. Some scientists have blamed volcanic activity or other culprits.

The die-off set up conditions that eventually allowed dinosaurs to rule the planet.

The newfound crater is more than twice the size of the Chicxulub crater in the Yucatan peninsula, which marks the impact that may have ultimately killed the dinosaurs 65 million years ago. The Chicxulub space rock is thought to have been 6 miles (10 kilometers) wide, while the Wilkes Land meteor could have been up to 30 miles (50 kilometers) wide, the researchers said.

Postdoctoral researcher Laramie Potts assisted in the discovery.

The work was financed by NASA and the National Science Foundation. The discovery, announced Thursday, was initially presented in a poster paper at the recent American Geophysical Union Joint Assembly meeting in Baltimore.

The researchers say further work is needed to confirm the finding. One way to do that would be to go there and collect rock from the crater to see if its structure matches what would be expected from such a colossal impact.

The crater, buried beneath a half-mile (1 kilometer) of ice and discovered by some serious airborne and satellite sleuthing, is more than twice as big as the one involved in the demise of the dinosaurs.

Sweet Mother Earth has had her troubles and will have them again. History repeats itself.