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Environment

Did Methane Cause the Mass Extinction That Made Way for the Dinosaurs?

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What's the News: Two hundred million years ago, half of the Earth's species vanished in the blink of a geological eye, clearing the way for rise of the dinosaurs in the Jurassic. The cause of that mass extinction, a new study suggests, may have been gigatons of methane released from the sea floor after a slight rise in the earth's temperature, triggering much greater warming. And if that sounds familiar, it's because scientists are worried the same thing will happen today. What's the Context:

  • The primary theory as to what went wrong at the end of the Triassic period, when this extinction took place, holds that tons of carbon dioxide released during the breakup of the supercontinent Pangaea ratcheted up global temperatures to deadly levels over the course of several hundreds of thousands of years.

  • But these researchers' work seems to indicate that the change took place even more quickly than that. In a previous study looking at limestone, which is the remains of ancient sea creatures, this team found that it disappeared from the geological record quite suddenly---a mere 20,000 years after the extinction event began.

  • For this study, they turned their attention to the cause of that extinction, looking into whether higher levels of methane could have been behind the warming event.

  • Methane is a much more potent greenhouse gas than carbon dioxide, and although most of the planet's reserves are presently locked up in the seafloor (as methane hydrate), it does gradually bubble up. Should rising temperatures melt the permafrost layers that keep arctic seafloor methane from escaping, we could see large amounts of methane leaking into the atmosphere very rapidly.

  • In fact, researchers have already the blame for other rapid warming events on oceanic methane, notably the most extreme known climate event, the Paleocene-Eocene Thermal Maximum.

How the Heck:

  • The researchers examined the remains of plants from that 20,000-year period, deposited on the shores of the ancient Tethys Sea. With a technique that determines whether a plant's carbon molecules were originally from carbon dioxide and methane, they looked for signs of each gas's presence in the atmosphere.

  • What they found was first a spike in carbon dioxide, then a massive amount of methane, supporting the idea that methane may have been released after a warming caused by carbon dioxide from seismic activity.

The Future Holds:

  • The team's findings are intriguing. Much is still unclear, though, about how such a carbon dioxide-methane loop would work. How hot would the atmosphere have to get before the permafrost layer melts? How much methane is there really in the seafloor? What other factors have to coincide with warming to have this effect? More research, likely with computer models, is needed on this topic to establish how such methane release might have worked at the end of the Triassic---and how it relates to our situation today.

Reference: Ruhl, et al. Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction. Science 22 July 2011, DOI: 10.1126/science.1204255

Image credit: Alfred F. Harrell (Smithsonian Institution), via flickr user public.resource.org

(via Wired Science

)

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