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

[Ron Baalke]

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/


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