A massive methane explosion frothing out of the world's oceans 250 million years ago caused the Earth's worst mass extinction, claims a US geologist. Similar, smaller-scale events could have happened since, which might explain the Biblical flood, for example, suggests Gregory Ryskin of Northwestern University in Evanston, Illinois1. And they could happen again: "It's a very conjectural idea but it's too important to ignore," says Ryskin. Up to 95% of Earth's marine species disapeared at the end of the Permian period. Some 70% of land species, including plants, insects and vertebrates, also perished. "It's arguably the single most important event in biology but there's no consensus as to what happened," says palaeontologist Andrew Knoll of Harvard University in Cambridge, Massacheusetts. Ryskin contends that methane from bacterial decay or from frozen methane hydrates in deep oceans began to be released. Under the enormous pressure from water above, the gas dissolved in the water at the bottom of the ocean and was trapped there as its concentration grew.Just one disturbance - a small meteorite impact or even a fast moving mammal - could then have brought the gas-saturated water closer to the surface. Here it would have bubbled out of solution under the reduced pressure. Thereafter the process would have been unstoppable: a huge overturning of the water layers would have released a vast belch of methane.
View: Full Article | Source: nature.com