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

[Ron Baalke]

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.