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

[Ron Baalke]

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 @ le.ac.uk .