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An asteroid impact.. not volcanism.. may have made Earth unlivable for dinosaurs

For decades, scientists have gone back and forth about whether massive volcanic eruptions or an asteroid impact — or maybe both — caused a mass extinction that saw the demise of all nonbird dinosaurs about 66 million years ago.

Now, geologic evidence and data on dinosaur habitats, combined with climate and ecological simulations, suggest it wasn’t the volcanism. Instead, a decades-long cold winter triggered by the giant impact wiped out dinosaur habitats and made it impossible for the creatures to survive, researchers report June 29 in Proceedings of the National Academy of Sciences.

In a plot twist, volcanism at the Deccan Traps, in what is now India, may have actually ameliorated the negative effects of the long winter, warming the planet quicker than would have occurred otherwise and allowing mammals room to thrive, the researchers say.

“It’s a complete change in the narrative of Deccan volcanism … [which] may well have been the benevolent hero of the time,” says Alexander Farnsworth, a paleoclimatologist at the University of Bristol in England.

The new research adds to a growing body of evidence that suggests the impact, not the eruptions, caused the die-off, including a recent study suggesting the bulk of volcanic outgassing happened either too early or too late to have caused the mass extinction (SN: 1/16/20).

An estimated 75 percent of the planet’s plant and animal species disappeared in a relative blink of an eye during the extinction event at the end of the Cretaceous Period. Previous research has indicated that a giant asteroid impact, at Chicxulub in what’s now the Yucatán Peninsula in Mexico, released enough ash, dust and gases to block out the sun and dramatically cool the planet for an extended period of time (SN: 11/2/17), possibly causing the extinction.

But around the same time, Deccan Traps eruptions released massive amounts of climate-altering gases too, as well as hundreds of thousands of cubic kilometers of lava, although the timing is uncertain. Such intense volcanism and associated bursts of gases have triggered other mass extinctions, such as the “Great Dying” at the end of the Permian Period 252 million years ago (SN: 12/6/18). As a result, the Deccan Traps still hadn’t been ruled out as the main culprit of the dinos’ die-off.

Farnsworth, paleontologist Alfio Alessandro Chiarenza of University College London and their colleagues evaluated how different dinosaur habitats would be affected under various impact and volcanism scenarios. The team ran dozens of climate and ecological simulations and compared the simulations with geologic evidence for the amount and types of gases spewed out by the eruptions, as well as with evidence of the dust kicked up into the atmosphere from crust pulverized by the asteroid impact.

Source: Science News

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