[meteorite-list] Evidence of Meteor Impact Found Off Australian Coast

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu May 13 15:00:52 2004
Message-ID: <200405131900.MAA28682_at_zagami.jpl.nasa.gov>

Donald Savage
Headquarters,Washington May 13, 2004
(Phone: 202/358-1547)

Cheryl Dybas
National Science Foundation, Arlington, Va.
(Phone: 703/292-7734)

Gail Gallessich
University of California, Santa Barbara
(Phone: 805/893-7220)

RELEASE: 04-159

EVIDENCE OF METEOR IMPACT FOUND OFF AUSTRALIAN COAST

     An impact crater believed to be associated with the
"Great Dying," the largest extinction event in the history of
life on Earth, appears to be buried off the coast of
Australia.

NASA and the National Science Foundation (NSF) funded the
major research project headed by Luann Becker, a scientist at
the University of California, Santa Barbara (UCSB). Science
Express, the electronic publication of the journal Science,
published a paper describing the crater today.

Most scientists agree a meteor impact, called Chicxulub, in
Mexico's Yucatan Peninsula, accompanied the extinction of the
dinosaurs 65 million years ago. But until now, the time of
the Great Dying 250 million years ago, when 90 percent of
marine and 80 percent of land life perished, lacked evidence
and a location for a similar impact event.

Becker and her team found extensive evidence of a 125-mile-
wide crater, called Bedout, off the northwestern coast of
Australia. They found clues matched up with the Great Dying,
the period known as the end-Permian. This was the time period
when the Earth was configured as one primary land mass called
Pangea and a super ocean called Panthalassa.

During recent research in Antarctica, Becker and her team
found meteoric fragments in a thin claystone "breccia" layer,
pointing to an end-Permian event. The breccia contains the
impact debris that resettled in a layer of sediment at end-
Permian time.

They also found "shocked quartz" in this area and in
Australia. "Few Earthly circumstances have the power to
disfigure quartz, even high temperatures and pressures deep
inside the Earth's crust," Becker said.

Quartz can be fractured by extreme volcanic activity, but
only in one direction. Shocked quartz is fractured in several
directions and is therefore believed to be a good tracer for
the impact of a meteor.

Becker discovered oil companies in the early 70's and 80's
had drilled two cores into the Bedout structure in search of
hydrocarbons. The cores sat untouched for decades. Becker and
co-author Robert Poreda went to Australia to examine the
cores held by the Geological Survey for Australia in
Canberra. "The moment we saw the cores, we thought it looked
like an impact breccia," Becker said. Becker's team found
evidence of a melt layer formed by an impact in the cores.

In the paper, Becker documented how the Chicxulub cores were
very similar to the Bedout cores. When the Australian cores
were drilled, scientists did not know exactly what to look
for in terms of evidence of impact craters.

Co-author Mark Harrison, from the Australian National
University in Canberra, determined a date on material
obtained from one of the cores, which indicated an age close
to the end-Permian era. While in Australia on a field trip
and workshop about Bedout, funded by the NSF, co-author Kevin
Pope found large shocked quartz grains in end-Permian
sediments, which he thinks formed as a result of the Bedout
impact. Seismic and gravity data on Bedout are also
consistent with an impact crater.

The Bedout impact crater is also associated in time with
extreme volcanism and the break-up of Pangea. "We think that
mass extinctions may be defined by catastrophes like impact
and volcanism occurring synchronously in time," Becker said.
"This is what happened 65 million years ago at Chicxulub but
was largely dismissed by scientists as merely a coincidence.
With the discovery of Bedout, I don't think we can call such
catastrophes occurring together a coincidence anymore," she
added.

For information and images about the research on the
Internet, visit:

http://beckeraustralia.crustal.ucsb.edu/

For information about NASA's Astrobiology research on the
Internet, visit:

http://astrobiology.arc.nasa.gov/


-end-
Received on Thu 13 May 2004 03:00:40 PM PDT