[meteorite-list] Volcanic Gases, Not Meteors, May Have Caused Mass Extinctions

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Mar 14 10:31:05 2006
Message-ID: <200603132302.k2DN24D07372_at_zagami.jpl.nasa.gov>

http://www.ens-newswire.com/ens/mar2006/2006-03-13-05.asp

Volcanic Gases, Not Meteors, May Have Caused Mass Extinctions
Environment News Service
March 13, 2006

LEICESTER, UK, March 13, 2006 (ENS) - Earth's history has been
punctuated by mass extinctions that have rapidly wiped out nearly all
life forms on the planet. To determine what caused these events, British
geologists are challenging the currently held theory that meteorite
impacts are to blame for wiping out the dinosaurs 65 million years ago
and other mass extinctions.

Professor Andy Saunders and Dr. Marc Reichow are testing the theory that
gases released by volcanic activity led to a prolonged volcanic winter
brought on by sulphur-rich aerosols, followed by a period of warming
induced by carbon dioxide in the atmosphere.

Flood basalt eruptions correspond with all main mass extinctions, says
Saunders, within error of the techniques used to determine the age of
the volcanism. Flood basalt eruptions are vast outpourings of lava that
covered large areas of the Earth's surface, creating what geologists
call flood basalt provinces.

Saunder says, these flood basalt events may have released enough
greenhouse gases - sulfur dioxide (SO2) and carbon dioxide (CO2) - to
"dramatically change the climate."

The largest flood basalt provinces on Earth, known as traps, coincide
with the largest extinctions. The Siberian Traps correspond with the end
of the Permian era some 251 million years ago when around 95 percent of
all living species died out. The Deccan Traps in India correspond with
the end of the Cretaceous era, some 65 million years ago when the
dinosaurs disappeared, leaving only fossils.

Saunders and Reichow at Leicester, in collaboration with Anthony Cohen,
Steve Self, and Mike Widdowson at the Open University, have recently
been awarded a Natural Environment Research Council grant to study the
Siberian Traps and their environmental impact.

The Siberian Traps are the largest known continental flood basalt
province. Erupted about 250 million years ago at high latitude in the
northern hemisphere. A scientific debate is underway concerning the
origin of these provinces and their environmental impact that this
research team hopes to clarify.

Using radiometric dating techniques, they hope to constrain the age and,
combined with geochemical analysis, the extent, of the Siberian Traps.

Measuring how much gas was released during these eruptions 250 million
years ago is "a considerable challenge," Saunders says.

The researchers will study microscopic inclusions trapped in minerals of
the Siberian Traps rocks to estimate the original gas contents. Using
these data they hope to be able to assess the amount of SO2 and CO2
released into the atmosphere 250 million years ago, and whether or not
this caused climatic havoc, wiping out nearly all life on Earth.

By studying the composition of sedimentary rocks laid down at the time
of the mass extinction, they also hope to detect changes to seawater
chemistry that resulted from major changes in climate.

>From these data Professor Saunders and his team hope to link the
volcanism to the extinction event. "If we can show, for example, that
the full extent of the Siberian Traps was erupted at the same time, we
can be confident that their environmental effects were powerful," said
Saunders. "Understanding the actual kill mechanism is the next stage."

The idea that meteorite impacts caused mass extinctions has been in
fashion over the last 25 years, since Louis Alverez's research team in
Berkeley, California published their work about an extraterrestrial
iridium anomaly found in 65 million year old layers at the
Cretaceous-Tertiary boundary.

This anomaly only could be explained by an extraterrestrial source, a
large meteorite, hitting the Earth and ultimately wiping out the
dinosaurs and many other species, according to Alverez.

Professor Saunders observed, "Impacts are suitably apocalyptic. They are
the stuff of Hollywood. It seems that every kid's dinosaur book ends
with a bang. But are they the real killers and are they solely
responsible for every mass extinction on Earth?"

There is scant evidence of impacts at the time of other major
extinctions such as at the end of the Permian, 251 million years ago,
and at the end of the Triassic, 200 million years ago. Saunders says the
evidence that has been found does not seem large enough to have
triggered an extinction at these times.

Dr. Michael Benton, a professor of paleontology at Bristol University,
is also studying the extinctions of 251 million years ago. "Over the
past decade or so, new discoveries in the field and important progress
in dating techniques have given us a more precise picture of this
period," he wrote in April 2005.

The suddenness and the scale of the event first suggested a collision
with an asteroid or other meteor. Recent paleontological data suggest a
different cause, Benton wrote in "RTD Info," a magazine on European
research.

Volcanic eruptions over 600, 000 years shook the only continent existing
251 million years ago, Pangaea. Huge eruptions occurred in what is now
Siberia, spreading basaltic lava onto the Earth's surface across an area
equivalent to the size of Europe to a depth of between 400 and 3,000
meters - the Siberian Traps. Recent dating techniques place these
eruptions at the end of the Permian era, Benton and Saunders' team both
say.

"Volcanism, and the colossal CO2 emissions that accompany it, are today
seen by many scientists as the element that triggered the array of
factors at the origin of this brutal crisis," Benton wrote.

As far back as 1991, two American scientists suggested that the volcanic
activity in Siberia was linked with the end-Permian extinctions.

The work by Paul Renne of the Institute of Human Origins in Berkeley,
California, and Asish Basu of the University of Rochester indicates that
the volcanic activity occurred very rapidly.

"This eruption occurred over an extremely short period of time,
geologically speaking," said Renne in 1991. "We believe we've nailed the
date down fairly precisely. It's even conceivable that it occurred over
an interval as short as 200,000 years."

There are other suggestions that atmospheric hydrogen sulfide and carbon
dioxide led to the mass extinctions.

In February 2005, Pennsylvania State geoscientist Dr. Lee Kump, studying
bacteria in deep sea sediments, said the volcanic eruptions in Siberia
250 million years ago in the end-Permian period, may have started a
cascade of events leading to high hydrogen sulfide levels in the oceans
and atmosphere and precipitating the largest mass extinction in Earth's
history.

"The recent dating of the Siberian trap volcanoes to be contemporaneous
with the end-Permian extinction suggests that they were the trigger for
the environmental events that caused the extinctions," wrote Kump in
2005. "But the warming caused by these volcanoes through carbon dioxide
emissions would not be large enough to cause mass extinctions by itself."

As the levels of atmospheric oxygen fell and the levels of hydrogen
sulfide and carbon dioxide rose, the upper levels of the oceans could
have become rich in hydrogen sulfide. Kump says this would kill most the
oceanic plants and animals and the hydrogen sulfide dispersing in the
atmosphere would kill most terrestrial life.

"A hydrogen sulfide atmosphere fits the extinction better than one
enriched in carbon dioxide," says Kump. "Carbon dioxide would have a
profound effect on marine life, but terrestrial plants thrive on carbon
dioxide, yet they are included in the extinction."

Another piece in the puzzle surrounding the end-Permian extinction is
that hydrogen sulfide gas destroys the ozone layer. Recently, Dr. Henk
Visscher of Utrecht University and his colleagues suggested that there
are fossil spores from the end-Permian that show deformities that
researchers suspect were caused by ultraviolet light.

"These deformities fit the idea that the ozone layer was damaged,
letting in more ultraviolet," says Kump.

Once this process is underway, methane produced in the ample swamps of
this time period has little in the atmosphere to destroy it. The
atmosphere becomes one of hydrogen sulfide, methane and ultraviolet
radiation.

More about the research on Siberian Traps is online at:

http://www.le.ac.uk/gl/ads/SiberianTraps/Index.html
Received on Mon 13 Mar 2006 06:02:04 PM PST