Methane Fingered For Permian Mass Extinction

[Richard W Travsky <rtravsky@uwyo.edu>]

http://www.newscientist.com/news/news.jsp?id=ns99992088

The release of massive clouds of methane from icy hydrates buried under
shallow ocean floors is the leading suspect for the most devastating
extinction in the fossil record, according to a new analysis.

Methane best matches the unusual carbon-isotope fingerprints found at the
scene of the crime, says Robert Berner of Yale University in Connecticut,
US, though it cannot explain atmospheric carbon dioxide levels at the time. 
...
Many theories have been proposed to explain the extinction, including a
comet or asteroid impact. Other ideas focus on two unusual events at the
end of the Permian - the eruptions of two million cubic kilometres of lava
across Siberia and unusual stratification of the oceans. 
...
Berner used his models of global carbon cycles to compare theoretical
predictions with data showing a sharp relative decrease in levels of the
carbon-13 isotope at the Permo-Triassic boundary. Because life prefers the
lighter carbon-12, that change shows large releases of organic carbon.
Berner also evaluated atmospheric carbon dioxide and its impact on global
temperatures.

Carbon-13 ratios are low in methane hydrates, so the catastrophic release
of four trillion tons of methane could produce the isotope ratios found in
rocks. Possible reasons for the mass destabilisation of the frozen gases
include large shock waves from meteorite impacts, strong greenhouse
warming or a dramatic reduction in sea level.

Yet Berner says even such a vast cloud of methane would not be enough to
produce a killing greenhouse heat wave or to poison the atmosphere,
because atmospheric oxygen quickly converts methane to carbon dioxide.

But other the theories fared worse. "Volcanoes can't explain the isotopic
excursion," Berner told New Scientist. Neither could the decay of a whole
biosphere of dead plants and animals. Overturn of a highly stratified
ocean could not explain observations unless the water was unrealistically
acidic.