"Smoking Gun" Is Elusive
Scientists have found strong links between other mass extinctions and volcanic activity.
"At least two other great extinctions may have had massive volcanic activity as a prime cause: the greatest of all extinctions, at the Permian-Triassic boundary 251 million years ago, and the mass extinction at the Triassic-Jurassic boundary 200 million years ago," said Hans-Dieter Sues, associate director for research and collections at the Smithsonian Institution's National Museum of Natural History.
"In each of these cases, there are vast areas of volcanic activity far exceeding the Deccan Traps in area and volume." Scientists say the Deccan Traps undoubtedly had a significant impact on the planet, but the volcanic event's precise role in the Cretacious-Tertiary's great extinction remains unknown.
"It would be inconceivable that you could have an eruption on this scale without having some sort of global climate effect," said Thomas Holtz, a vertebrate paleontologist at the University of Maryland in College Park.
"Certainly it would have made life difficult for organisms all over the world," he added. "But it is yet to be shown that there was an extinction associated with these eruptions."
Holtz suggests that dinosaurs may have been stressed by the effects of the Deccan Traps eruptions. But they survived until the arrival of a city-sized asteroid that plowed into Mexico's Yucatán Peninsula 65 million years ago.
The so-named Chicxulub impact clouded the planet's atmosphere with enormous volumes of ash and debris and is commonly thought to be a cause of the Cretaceous-Tertiary extinction.
"We have evidence of all sorts of animals, in the sea and on land, occurring right up to the [Cretaceous-Tertiary] boundary. Those species were surviving whatever effects the Deccan Traps produced," Holz said.
Both Hotlz and Sues, of the Smithsonian, suggest that a number of events, including the massive lava flows and the subsequent catastrophic asteroid impact, as well as mountain building and changing global sea levels, might have worked combination to snuff out the dinosaurs.
"Maybe a massive extinction can't have a single cause," Holtz speculated. "Maybe they are always one-two punches, where something happens to cause environmental stress, species cope to some degree; and then something else comes along that is additionally catastrophic, so that [species] can't recover."
Chenet, of the Paris Geophysical Institute, agrees that India's ancient volcanic eruptions and the Chicxulub asteroid impact produced a deadly combination. But she suggests that the lava flows might well have finished the job on their own.
"Our view is that [asteroid] impact added to the stress already generated by an ongoing massive eruption, enhancing significantly the extent of the extinction, which would, however, have taken place even if the impact had not occurred."
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