[meteorite-list] Volcanic Eruptions Pushed Dinosaurs Over Edge?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 16 11:09:23 2005
Message-ID: <200508161508.j7GF88h02979_at_zagami.jpl.nasa.gov>

http://www.iol.co.za/index.php?set_id=14&click_id=143&art_id=vn20050816070717875C697517

'Climate change pushed dinosaurs over edge'
Steve Connor
www.iol.co.za (South Africa)
August 16, 2005

London - One of the most violent volcanic eruptions on Earth may have
triggered the demise of the dinosaurs.

Many scientists believed a giant asteroid caused the mass extinction 65
million years ago when its collision with the Earth caused a dramatic
change in the global climate, which dinosaurs were unable to survive.

However, a new study points to a more complex environmental catastrophe
that was started when a massive series of volcanic eruptions took place
in what is now north-western India.

The Deccan Traps in the Indian state of Maharashtra are one of the
Earth's largest flows of volcanic lava resulting from colossal
outpourings of molten rock and ash - the solidified lava flows today are
more than 1,6km deep and cover about 320 000km2.

Volcanologists have long thought that the eruption, which has been dated
to about 65 million years ago, could have been responsible for the
demise of the dinosaurs by releasing vast amounts of dust, sulphur and
greenhouse gases into the atmosphere.

One problem was that the Deccan Traps did not result from a single
eruption but a series of eruptions that occurred over a long period,
perhaps a million years, which would have given the climate plenty of
time to adjust.

Now a new study of the Deccan Traps has shown that at least a major part
of the total eruption occurred over a much shorter period of time than
hitherto thought possible - perhaps less than 30 000 years - which would
have caused sudden and dramatic changes to the climate, affecting all
life on Earth.

Anne-Lise Chenet of the Institut de Physique du Globe de Paris and her
geophysicist colleague, Vincent Courtillot, analysed the magnetic
signatures of the rock stored in cores that they had drilled through the
lava flows.

This magnetic data shows just how rapidly the lava formed.

"Our working hypothesis is that the majority of the total volume of lava
might have been erupted in only a few major events spread over only a
small fraction of millennia," Chenet said.

The scientists have calculated that at least 660m of lava were deposited
in 30 000 years, which would have released enough sulphur gases in a
relatively short period of geological history to alter the global
climate dramatically, as well as poisoning the seas with acid.

Furthermore, the scientists have also found evidence that the Deccan
Traps were in the midst of erupting when the giant asteroid crashed into
what is now Chicxulub in Mexico's Yucatan peninsula.

The signature of the asteroid collision - iridium deposits from the
meteorite found buried in 65 million-year-old sediments around the world
- are also present within the lava cores of the Deccan Traps.

This proves that the collision occurred during the eruptions - a
spectacular and almost unprecedented double whammy for life on Earth.

Mike Widdowson, a volcanologist from the Open University in Milton
Keynes, who has worked with the French team, said it now seemed that the
demise of the dinosaurs may have begun with global climate change
brought about by the volcanic eruptions and ended with the Chicxulub
asteroid.

"The Deccan eruptions pre-conditioned the global environment toward a
catastrophic tipping point before the Chicxulub impact occurred.
Chicxulub was the coup de grace," Widdowson said.

The findings also fit the findings of palaeontologists who have shown
from studying the bones of dinosaurs that many species were in demise
thousands of years before the Chicxulub impact.

"Palaeontologists say the decline in the dinosaurs began long before the
Chicxulub impact.

"We would argue that they were being poisoned due to the Deccan Traps,"
Dr Widdowson said.

It was not just the dinosaurs that went extinct 65 million years ago.
Scientists estimate that between 80 and 90 percent of marine species
died out and about 85 percent of land species, with all land animals
larger than about 22,5kg being wiped away.
Received on Tue 16 Aug 2005 11:08:06 AM PDT