EVANSTON, Ill. -- What caused the worst mass extinction in Earth's history 251 million years ago? An asteroid or comet colliding with Earth? A greenhouse effect? Volcanic eruptions in Siberia? Or an entirely different culprit? A Northwestern University chemical engineer believes the culprit may be an enormous explosion of methane (natural gas) erupting from the ocean depths.

In an article published in the September issue of Geology, Gregory Ryskin, associate professor of chemical engineering, suggests that huge combustible clouds produced by methane gas trapped in stagnant bodies of water and suddenly released could have killed off the majority of marine life and land animals and plants at the end of the Permian era -- long before dinosaurs lived and died.

The mechanism also might explain other extinctions and climate perturbations (ice ages) and even the Biblical flood, as well as be the cause of future catastrophes.

Ryskin calculated that some 10,000 gigatons of dissolved methane could have accumulated in water near the ocean floor under high pressure. If released quickly, perhaps triggered by an earthquake, the resulting cloud of methane would have an explosive force about 10,000 times greater than the world's entire stockpile of nuclear weapons. The huge conflagrations plus flooding and overturned oceans would cause the extinctions. (Approximately 95 percent of marine species and 70 percent of land species were lost.)

"That amount of energy is absolutely staggering," said Ryskin. "As soon as one accepts this mechanism, it becomes clear that if it happened once it could happen again. I have little doubt there will be another methane-driven eruption -- though not on the same scale as 251 million years ago -- unless humans intervene."