Signs of Crater Linked to Mass Extinction Said Found

The world was not a great place to be 250 million years ago. That's because
some 90 percent of the planet's marine life and 80 percent of life on land
had gone extinct at the end of the Permian period. Exactly what caused the
mass extinction is a matter of debate, with the two leading theories
positing massive volcanism in Siberia or a collision with a meteor much like
the one that killed the dinosaurs 65 million years ago. New findings
published online today by the journal Science bolster the impact hypothesis
and argue that the resulting crater lies buried off the coast of northwest
Australia.

Luann Becker of the University of California at Santa Barbara and her
colleagues studied two cores drilled by oil companies in the 1970s and 1980s
into a geologic structure off the Australian coast known as the Bedout High.
"The moment we saw the cores we thought it looked like an impact breccia,"
Becker says. Specifically, the team found what they say is evidence of a
telltale melt layer that formed when a meteor crashed into the earth and
created the 125-mile-wide Bedout. Additional support for their contention
that Bedout is an impact crater comes from the fact that material from the
cores dates to 250 million years ago, give or take 4.5 million years.
Together with earlier evidence that Becker and her team collected in
Antarctica and Australia--including shocked quartz and molecules called
fullerenes containing extraterrestrial helium and argon--the new results
provide further evidence that a massive impact brought about the Great
Dying, the scientists say. "We think that mass extinctions may be defined by
catastrophes like impact and volcanism occurring synchronously in time,"
Becker remarks. "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."

Read the rest at Scientific American
http://cl.extm.us/?fe861279716501757d-fe3016707360067c711779

Posted by
Robert Karl Stonjek.
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