Methane Caused Extinctions

July 27, 2000 -- Huge reservoirs of methane trapped beneath the ocean floorrapidly escaped during prehistoric global warming and depleted muchof the sea’s oxygen, according to new research into why many formsof life suddenly vanished 183 million years ago.

The findings, reported in today’s issue of the journalNature, shed new light not only on the disappearance of as many as80 percent of some deep-sea species, but also on a process suspected inother prehistoric mass extinctions.

The study also raised questions about today’s sea floorreservoir of methane hydrate, which the federal government plans tostudy as a possible energy source.

Algae Fuel

“One of the important questions that is debated a lot today isthe stability of this methane hydrate reservoir and how easy it isto release the methane that is there,” said Stephen Hesselbo, anOxford University researcher and the study’s lead author.

Methane hydrate is formed beneath the sea floor when algae fromthe surface dies and sinks. Normally a gas, the methane is lockedin an ice-like state but is susceptible to changes in pressure andtemperature.

In the latest research, the Oxford scientists studied fossilwood deposits and identified a signal that they say indicates anunusual level of light carbon in the Earth’s atmosphere.

“It’s a question of trying to identify what the source of thelight carbon would be,” Hesselbo said. “The best explanation inthis case is that it comes from methane — methane hydrate fromocean margin sediment.”

Oxygen Consumer

The researchers believe massive volcanic eruptions during theJurassic period initiated global warming by spewing carbon dioxideand other greenhouse gases into the atmosphere. Deep-sea currentsalso were affected.

Methane, freed from its suboceanic cage by warmer water, thenused the oxygen in the water or atmosphere to form carbon dioxide.In either case, it would have accelerated global warming.

“A number of important fossil groups disappeared at exactlythat time,” Hesselbo said. “The extinction and the associationwith the lack of oxygen has been fairly well established, but theassociation with methane release is something that hasn’t beenrealized before.”

Hardest hit were bottom-feeding clam-like organisms known asbivalves: An estimated 80 percent of the species disappeared.Others affected included ostracods, belemnites and some marineplants.

Explosive Release

The researchers believe the event took place over a period of5,000 years — a blink in geologic time. The release was estimatedto be 20 percent of the present-day 14,000 billion tons of gashydrate on the sea floor.

“It’s an interesting novel explanation, and it seems to accountfor the geochemical data that they have,” said David Ottjer, apaleontologist and Earth sciences professor at the University ofSouthern California.

“They have to wiggle a fair bit to get to where they want to gofor their solution, but they may be right,” he said. “It’s notnecessarily that they’ve found the absolute smoking gun, butthey’re probably on the right track.

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