[meteorite-list] Mass Extinctions -- A Threat from Outer Space or Our Own Planet's Detox?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Mar 9 11:58:28 2006
Message-ID: <200603091656.k29GuR922440_at_zagami.jpl.nasa.gov>

Press and Publications Office
University of Leicester
Leicester, U.K.

09/03/2006

Mass Extinctions -- A Threat from Outer Space or Our Own Planet's Detox?

University scientists suggest extraterrestrial theories are flawed and
that more down to earth factors could have accounted for past mass
extinctions

Earth history has been punctuated by several mass extinctions rapidly
wiping out nearly all life forms on our planet. What causes these
catastrophic events? Are they really due to meteorite impacts? Current
research suggests that the cause may come from within our own planet --
the eruption of vast amounts of lava that brings a cocktail of gases from
deep inside the Earth and vents them into the atmosphere.

University of Leicester geologists, Professor Andy Saunders and Dr Marc
Reichow, are taking a fresh look at what may actually have wiped out the
dinosaurs 65 million years ago and caused other similarly cataclysmic
events, aware they may end up exploding a few popular myths.

The idea that meteorite impacts caused mass extinctions has been in vogue
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 the dinosaurs --
and many other organisms -- off the Earth's surface.

Professor Saunders commented: "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 e.g., at the end of the Permian, 250
million years ago, and at the end of the Triassic, 200 million years ago.
The evidence that has been found does not seem large enough to have
triggered an extinction at these times."

Flood basalt eruptions are -- he says -- an alternative kill mechanism.
These do correspond with all main mass extinctions, within error of the
techniques used to determine the age of the volcanism. Furthermore, they
may have released enough greenhouse gases (SO2 and CO2) to dramatically
change the climate. The largest flood basalts on Earth (Siberian Traps and
Deccan Traps) coincide with the largest extinctions (end-Permian, and
end-Cretaceous). "Pure coincidence?", ask Saunders and Reichow.

While this is unlikely to be pure chance, the Leicester researchers are
interested in precisely what the kill mechanism may be. One possibility is
that the gases released by volcanic activity lead to a prolonged volcanic
winter induced by sulphur-rich aerosols, followed by a period of
CO2-induced warming.

Professor Andy Saunders and Dr. Marc Reichow at Leicester, in
collaboration with Anthony Cohen, Steve Self, and Mike Widdowson at the
Open University, have recently been awarded a NERC (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, they are one of many known flood basalts provinces --
vast outpourings of lava that covered large areas of the Earth's surface.
A major debate is underway concerning the origin of these provinces --
including the Siberian Traps -- and their environmental impact.

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. 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. He explained: "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. Understanding
the actual kill mechanism is the next stage ... watch this space."

More information is available from the website:
     http://www.le.ac.uk/gl/ads/SiberianTraps/Index.html

Note to editors:

Further information is available from Professor Andy Saunders, Department
of Geology, University of Leicester, tel 0116 252 3923; or from Dr Marc
Reichow, email: mkr6 _at_ le.ac.uk .
Received on Thu 09 Mar 2006 11:56:27 AM PST