[meteorite-list] Study: Biggest Extinction Caused By Lava Flow

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:31 2004
Message-ID: <200206062240.PAA00541_at_zagami.jpl.nasa.gov>

http://www.cnn.com/2002/TECH/science/06/06/volcanic.extinction.ap/index.html

Study: Biggest extinction caused by lava flow

Samples age-dated at about 250 million years
June 6, 2002

WASHINGTON (AP) -- A massive flow of molten rock, bubbling to the surface
and spreading more than a mile deep over an area half the size of Australia,
may have killed up to 90 percent of all animal species on Earth some 250
million years ago, a study suggests.

The study shows that the flood of molten rock that created what is known as
the Siberian Traps in Russia was almost twice as big as previously believed
and could have continued for thousands of years, changing the climate of the
entire planet.

The researchers, a group of United Kingdom and Russian scientists, say in a
report to appear Friday in the journal Science that such an eruption of
flood basalt would have filled the atmosphere with a choking concentration
of sulfur dioxide, carbon dioxide and other gasses, making it difficult for
any species to survive.

Samples from the lava flow have been age-dated at about 250 million years.
Other studies have shown during this same period the Earth experienced its
most extensive extinction crisis -- a die-off that killed at least 90
percent of ocean species and more than 70 percent of land creatures.

Called the Permian-Triassic extinction, it is a key event in the history of
the planet. It was followed by the rise of the dinosaurs, the animal species
that dominated the Earth, until they too went extinct about 65 million years
ago.

In the study, the researchers analyzed samples drilled from deep below the
floor of a basin beside the known Siberian Traps. They found that the basin
was underlain with the same type and age of lava that created the Traps.

This means that the flood of lava that formed the Traps was at least twice
as massive and lasted perhaps twice as long as previously believed, they
said.

Asteroid theory

Such a large volume of lava spewing to the surface over hundreds of
thousands of years would inject millions of tons of chemicals into the
atmosphere, causing long-lasting changes in the climate and an ecological
collapse, they said.

"The larger area of volcanism strengthens the link between the volcanism and
the end-Permian mass extinction," the authors say in Science.

Some earlier studies have suggested that the Permian-Triassic extinction was
caused by an asteroid striking the Earth and wiping out much of life with a
sudden, single stroke.

But the evidence from the new study points toward a prolonged extinction
event, stretching over hundreds of thousands of years.

Peter D. Ward, professor of geological sciences and a paleontologist at the
University of Washington, said the United Kingdom and Russian study
reinforces what is becoming a widely accepted view of many other
researchers.

"It looks like the Earth was getting multiple levels of extinction," said
Ward. He said chemical studies of ancient geology suggest that plant
productivity was impacted "over and over again" during the period around the
Permian-Triassic boundary.

'Not a single event'

He said phased cycles of extinction, as evidenced in the geological record,
are compatible with a massive, prolonged flood of molten basalt.

"We don't see all of the basalt coming out at once, as a steady stream,"
said Ward. "It was not a single event" such as an asteroid impact.

This is in contrast to the extinction event that killed the dinosaurs. Ward
said many different studies show that an asteroid did deliver "a one-time
hit" on the Earth that caused rapid changes that snuffed out the dinosaurs.

Marc K. Reichow of the University of Leicester in the United Kingdom was
lead author of the study. Other researchers were from the Scottish
Universities Environmental Research Center in Scotland, and from the
Institute of Geochemistry and the Institute of Geology Oil and Gas, both in
Russia.
Received on Thu 06 Jun 2002 06:40:55 PM PDT