Washington: Gigantic volcanic eruptions may have wiped out half of Earth's species 200 million years ago, a new study has found. Scientists examining evidence across the world from New Jersey to North Africa said they have linked the abrupt disappearance of half of Earth's species 200 million years ago to a precisely dated set of gigantic volcanic eruptions.

The study sets a new precise date for the End-Triassic Extinction (ETE) - 201,564,000 years ago, exactly the same time as a massive outpouring of lava. "This may not quench all the questions about the exact mechanism of the extinction itself. However, the coincidence in time with the volcanism is pretty much ironclad," said co-author of the study Paul Olsen, a geologist at Columbia University's Lamont-Doherty Earth Observatory.

The new study reported in the journal Science, unites several pre-existing lines of evidence by aligning them with new techniques for dating rocks. Lead author Terrence Blackburn (then at Massachusetts Institute of Technology; now at the Carnegie Institution) used the decay of uranium isotopes to pull exact dates from basalt, a rock left by eruptions.

The basalts analysed in the study all came from the Central Atlantic Magmatic Province (CAMP), a series of huge eruptions known to have started around 200 million years ago, when nearly all land was massed into one huge continent. The eruptions spewed some 2.5 million cubic miles of lava in four sudden spurts over a 600,000-year span, and initiated a rift that evolved into the Atlantic Ocean; remnants of CAMP lavas are found now in North and South America, and North Africa.

The scientists analysed samples from what are now Nova Scotia, Morocco and the New York City suburbs. Blackburn and his colleagues showed that the eruption in Morocco was the earliest, with ones in Nova Scotia and New Jersey coming about 3,000 and 13,000 years later, respectively.

Among the creatures that vanished were eel-like fish called conodonts, early crocodilians, tree lizards and many broad-leaved plants. The dating is further strengthened by a layer of sediment just preceding the extinction containing mineral grains providing evidence of one of Earth's many periodic reversals of magnetic polarity.

This particular reversal, labelled E23r, is consistently located just below the boundary, making it a convenient marker, said coauthor Dennis Kent, a paleomagnetism expert at Lamont-Doherty.


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