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Mass Extinction at the End of the Triassic Caused by Volcanic Eruptions, Study Shows

Update Date: Mar 21, 2013 11:32 PM EDT

Scientists have finally solved the mystery surrounding the extinction of as much as half of Earth living organisms at the end of the Triassic period.

In a recent study, researchers point the finger to mega volcanic eruptions as being behind the mass extinction that opened the way for dinosaurs to conquer the Earth for 135 million years.

According to the study published Thursday on the journal Science, the eruptions were large enough to cover the United States under 300 feet of lava. And it happened roughly at the same time that vast numbers of plant and animal species disappeared from the fossil record.

Terrence Blackburn, a geologist at the Carnegie Institution for Science in Washington and lead investigator in the study, explained that “about 201 million years ago, tectonic forces started ripping the supercontinent known as Pangaea apart.”

“The underlying mantle rock melted, generating these large eruptions,” he added.

Blackburn went on explaining that the rift, which eventually created the Atlantic Ocean basin, happened between sections of Pangaea that would go on to become North America and Africa.

It was at about that time that the first bout of volcanic eruptions kicked off. During four periods, over 600, 000 years, these huge eruptions, or flood basalt events took place, wiping out a great deal of Earth’s plants and animals.

According to National Geographic, some ancient crocodilian ancestors, eel-like animals called conodonts, and a mammalian group called therapsids were all hammered, with many disappearing from the fossil record around this time.

What have researchers taking so long to settle this apparently straightforward mystery was that until now, the margin of error in calculating the timing of these eruptions was significantly high. Previous calculations were shrouded by an alarming one to three million years of error, which made it hard to determine which had happened first—the eruptions or the mass extinction.

The guiding light came by using a rare mineral called zircon, found in igneous rocks like basalts, the researchers were able to narrow down their margin of error to 20,000 to 30,000 years—pegging the initial eruptions to just before the mass extinction event.

“Zircon is a perfect time capsule for dating those rocks,” said Blackburn. When the mineral crystallizes, it incorporates uranium, which decays over a known time with respect to the element lead. By measuring the ratio of uranium to lead in our samples, we can determine the age of those crystals, he explained.

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