[meteorite-list] The biggest of the Antarctic meteorites...

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Fri Jun 2 21:50:34 2006
Message-ID: <uilv721coue611jiq756l6s142866inrhr_at_4ax.com>

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

Antarctic crater linked to ancient die-off
Scientists say impact might have caused extinction 250 million years ago
By Robert Roy Britt
Senior science writer
Space.com


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.

? 2006 Space.com. All rights reserved. More from Space.com.
Received on Fri 02 Jun 2006 02:11:58 AM PDT