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Clathrate gun hypothesis
The clathrate gun hypothesis states that as sea temperatures rise the sudden release of methane from methane clathrate compounds buried in the seabeds will cause a drastic alteration of the ocean environment and the atmosphere of earth, as recent analysis concerning the Permian extinction event indicates may have happened in the past.
Additional recommended knowledge
Methane clathrate, also called methane hydrate, is a form of water ice that contains a large amount of methane within its crystal structure. Extremely large deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. The sudden release of large amounts of natural gas from methane clathrate deposits in a runaway greenhouse effect could be a cause of past and future climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; it is thought that this is a main factor in the global warming of 6°C that happened during the end-permian extinction, as methane is much more powerful as a greenhouse gas than carbon dioxide (despite its atmospheric lifetime of around 12 years, it has a global warming potential of 62 over 20 years and 23 over 100 years). The theory also predicts this will greatly affect available oxygen content of the atmosphere.
In 2002, a BBC2 'Horizon' documentary, 'The Day the Earth Nearly Died,' summarized some recent findings and speculation concerning the Permian extinction event. Paul Wignall examined Permian strata in Greenland, where the rock layers devoid of marine life are tens of meters thick. With such an expanded scale, he could judge the timing of deposition more accurately and ascertained that the entire extinction lasted merely 80,000 years and showed three distinctive phases in the plant and animal fossils they contained. The extinction appeared to kill land and marine life selectively at different times. Two periods of extinctions of terrestrial life were separated by a brief, sharp, almost total extinction of marine life. Such a process seemed too long, however, to be accounted for by a meteorite strike. His best clue was the carbon isotope balance in the rock, which showed an increase in carbon-12 over time. The standard explanation for such a spike – rotting vegetation – seemed insufficient.
Geologist Gerry Dickens suggested that the increased carbon-12 could have been rapidly released by up-swellings of frozen methane hydrate from the seabed. Experiments to assess how large a rise in deep sea temperature would be required to sublimate solid methane hydrate suggested that a rise of 5°C (9 F) would be sufficient.
Possible release events
Two events possibly linked in this way are the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last ice age is thought not to be due to methane release.
Related mechanism: dissolved methane release
Focusing on the Permian-Triassic boundary, Gregory Ryskin  explores the possibility that mass extinction can be caused by an extremely fast, explosive release of dissolved methane (and other dissolved gases such as carbon dioxide and hydrogen sulfide) that accumulated in the oceanic water masses prone to stagnation and anoxia (e.g., in silled basins).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Clathrate_gun_hypothesis". A list of authors is available in Wikipedia.|