for National Geographic News
A six-mile-wide (ten-kilometer-wide) asteroid is thought to have carved out the Chicxulub crater off Mexico's Yucatán Peninsula, triggering worldwide climate changes that led to the mass extinction.
But the controversial new theory says the dinosaurs were actually finished off by another 25-mile-wide (40-kilometer-wide) asteroid. That space rock slammed into the planet off the western coast of India about 300,000 years after Chicxulub, experts say.
"The dinosaurs were really unlucky," said study co-author Sankar Chatterjee, a paleontologist at Texas Tech University in Lubbock.
Chatterjee thinks this second asteroid impact created a 300-mile-wide (500-kilometer-wide) depression on the Indian Ocean seafloor, which his team began exploring in 1996.
His team has dubbed this depression the Shiva crater, after the Hindu god of destruction and renewal.
"If we are correct," Chatterjee said, "this is the largest crater known on Earth."
Dinosaur-Killer Asteroid Boosted Volcanoes?
The Shiva asteroid impact was powerful enough to vaporize Earth's crust where it struck, allowing the much hotter mantle to well up and create the crater's tall, jagged rim, Chatterjee estimates.
What's more, his team thinks the impact caused a piece of the Indian subcontinent to break off and drift toward Africa, creating what are now the Seychelles islands (see map).
The Shiva impact may also have enhanced volcanic eruptions that were already occurring in what is now western India, Chatterjee added.
Some scientists have speculated that the noxious gases released by the Indian volcanoes, called the Deccan Traps, were crucial factors in the dinosaurs' extinction.
"It's very tempting to think that the impact actually triggered the volcanism," Chatterjee said.
"But that may not be true. It looks like the volcanism was already happening, and the [Shiva] impact just made it worse."
Research to be presented next week at the Annual Meeting of the Geological Society of America in Portland, Oregon.
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