Timeline of a Mass Extinction

A new study from NASA Astrobiology Program-funded scientists points to a rapid collapse of Earth's species 252 million years ago.

Since the first organisms appeared on Earth approximately 3.8 billion years ago, life on the planet has had some close calls. In the last 500 million years, Earth has undergone five mass extinctions, including the event 66 million years ago that wiped out the dinosaurs. And while most scientists agree that a giant asteroid was responsible for that extinction, there's much less consensus on what caused an even more devastating extinction more than 185 million years earlier.

The end-Permian extinction occurred 252.2 million years ago, decimating 90 percent of marine and terrestrial species, from snails and small crustaceans to early forms of lizards and amphibians. "The Great Dying," as it's now known, was the most severe mass extinction in Earth's history, and is probably the closest life has come to being completely extinguished. Possible causes include immense volcanic eruptions, rapid depletion of oxygen in the oceans, and -- an unlikely option -- an asteroid collision.

While the causes of this global catastrophe are unknown, an MIT-led team of researchers has now established that the end-Permian extinction was extremely rapid, triggering massive die-outs both in the oceans and on land in less than 20,000 years -- the blink of an eye in geologic time. The researchers also found that this time period coincides with a massive buildup of atmospheric carbon dioxide, which likely triggered the simultaneous collapse of species in the oceans and on land.

With further calculations, the group found that the average rate at which carbon dioxide entered the atmosphere during the end-Permian extinction was slightly below today's rate of carbon dioxide release into the atmosphere due to fossil fuel emissions. Over tens of thousands of years, increases in atmospheric carbon dioxide during the Permian period likely triggered severe global warming, accelerating species extinctions.

The researchers also discovered evidence of simultaneous and widespread wildfires that may have added to end-Permian global warming, triggering what they deem "catastrophic" soil erosion and making environments extremely arid and inhospitable.

The researchers present their findings this week in Science, and say the new timescale may help scientists home in on the end-Permian extinction's likely causes.

For more information: http://web.mit.edu/newsoffice/2011/mass-extinction-1118.html

Source: NAI Newsletter

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