Were volcanos responsible for some extinctions




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


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