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," explains
Dr. Becker.
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,"
Dr. Becker explains. "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," Dr. Becker adds.
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