Two hundred and fifty million years ago, the Permian extinction wiped out virtually all marine species and most life on land, clearing the path for the dinosaurs and setting back the rise of mammals by 50 million years. Gregory Ryskin of Northwestern University thinks he has tracked down the cause of this mysterious die-off, the worst in history: an underwater explosion, 10,000 times as powerful as the detonation of every nuclear weapon in the world today.
Ryskin proposes that huge deposits of methane and other gases, which are naturally produced in deep-sea waters, became trapped under the pressure of a then-stagnant global ocean. Any forceful disturbance—an earthquake or a volcanic eruption, for instance—could have disrupted the pressurized gas. Rising methane could have churned the oceans, suffocating aquatic organisms, and flooded into the atmosphere, triggering a worldwide hot spell. A single lightning strike could even have set the whole planet aflame. The explanation fits both the observed pattern of extinction and the evidence of a sudden influx of carbon dioxide (produced when methane burns or breaks down) in the atmosphere, Ryskin says.
Gregory Retallack of the University of Oregon, an expert on the Permian extinction, is dubious: “In that era, when we had one big ocean, the water would have been mixed quite well by currents. I don’t think you could store that much methane underwater.” Ryskin counters that his is the only hypothesis that fits all the known data, and he points out that minor gas belches still create hazards in lakes and coastal areas. He speculates that humans may have witnessed a scaled-down version of the Permian disaster 7,000 years ago, when a methane eruption in the Black Sea inspired the story of Noah’s ark.