By Culturekiosque Staff
PERTH, AUSTRALIA, 3 SEPTEMBER 2013 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 Goiás 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
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
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
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