[meteorite-list] Meteorite Crater in Brazil Reveals Biggest Extinction In Earth History

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat, 14 Sep 2013 16:37:03 -0700 (PDT)
Message-ID: <201309142337.r8ENb4VY014649_at_zagami.jpl.nasa.gov>

http://www.culturekiosque.com/nouveau/news/permian_extinction_animal825.html

Meteorite Crater in Brazil Reveals Biggest Extinction In Earth History
By Culturekiosque Staff
September 3, 2013

PERTH, AUSTRALIA - It's well known that the dinosaurs were wiped out 66
million years ago when a meteor hit what is now southern Mexico but evidence
is accumulating that the biggest extinction of all, 252.3m years ago,
at the end of the Permian period, was also triggered by an impact that
changed the climate.

While the idea that an impact caused the Permian extinction has been around
for a while, what's been missing is a suitable crater to confirm it. Associate
Professor Eric Tohver of the University of Western Australia's School
of Earth and Environment believes he has found the impact crater which
reveals though the trigger was the same, the details are significantly
different.

Last year Dr Tohver redated an impact structure that straddles the border
of the states of Mato Grosso and Goias in Brazil, called the Araguainha
crater, to 254.7m years, with a margin of error of plus or minus 2.5m
years. Previous estimates had suggested Araguainha was 10m years younger,
but Dr Tohver has put it within geological distance of the extinction
date.

The Chicxulub crater in Mexico, is 180km in diameter while the Araguainha
is 40 kilometres across and was thought to be too small to have caused
the chain reaction which brought about such mass extinction.

"I have been working with Fred Jourdan at Curtin University and UWA post-doctoral
fellow Martin Schmieder to establish better ages for various impact structures
in Australia and abroad. We were particularly interested in the Araguainha
crater, since the original age determined in the 1990s was relatively
close to the Permo-Triassic boundary. The refinements in geochronological
techniques that we are applying are helping to reveal the true age of
these structures," Dr Tohver said.

The results of an extensive geological survey of the Araguainha crater
funded by UWA and the Australian Research Council and published in Palaeogeography,
Palaeoclimatology, Palaeoecology, revealed that a sizeable amount of the
rock is oil shale. The researchers calculated that the impact would have
generated thousands of earthquakes of up to magnitude 9.9, significantly
more powerful than the largest recorded by modern seismologists for hundreds
of kilometres around, releasing huge amounts of oil and gas from the shattered
rock.

Dr Tohver believes the explosion of methane released into the atmosphere
would have resulted in instant global warming, making things too hot for
much of the planet's animal life.

"Martin Schmieder and I are currently working on documenting some of the
more extreme environmental effects of the impact, including giant tsunamis.
 In addition, ongoing work with Kliti Grice at Curtin University and her
Ph.D. student Ines Melendez will be fundamental to documenting changes
in the organic geochemistry of the target rocks," Dr Tohver said.

It's estimated more than 90 per cent of all marine species and about 70
per cent of land-based species disappeared in the Permian extinction.
Received on Sat 14 Sep 2013 07:37:03 PM PDT