Indian Impact Crater Hints of Another Dino-Killer

An impact crater in India suggests a meteor strike there may have killed off the dinosaurs.

Off the west coast of India, there is a suspicious basin called Shiva. It forms a rough ring over 500 kilometers (311 miles) in diameter and has a central underwater peak the size of Mt. McKinley. Where it sweeps on shore, the land appears shattered and riddled with faults and geothermal hot springs.

If Sankar Chatterjee of Texas Tech University is right, Shiva is the largest impact crater on the planet, the scar leftover from a cataclysm that had a hand in killing the dinosaurs.

The basin is a bonanza of oil and gas resources, and energy companies have been drilling in it for decades. Information on its rocks has trickled out slowly from company vaults, but Chatterjee has kept close tabs, suspecting for years that the region has a dramatic story to tell about a long-lost cosmic catastrophe.

So far the evidence he has assembled is mostly circumstantial. The bedrock that lines Shiva is rife with mantle rocks, as though Earth's crust was simply obliterated across a huge area. And the areas dating to the moment of the suspected impact 65 million years ago are rich in iridium -- a typical fingerprint of impacts.

Major questions about the area abound, though.

For one, a massive spate of volcanic eruptions known as the Deccan Traps overlaps the eastern edge of Shiva. The traps also appear to have erupted around 65 million years ago, just as the Cretaceous period -- and the reign of dinosaurs on Earth -- was coming to a crashing halt.

Were the two events related? Did one, or both contribute to the mass extinction that followed? And what about the Chicxulub impact basin in Mexico, which has already been blamed as the dinosaurs' killer?

"The idea of Shiva as an impact basin is still very speculative," Chatterjee admitted. "But it tends to explain so many things."

For one, the Chicxulub asteroid is thought to be between 8 and 10 kilometers (5.0 and 6.2 miles) wide, a pipsqueak by Shiva's standards.

Chatterjee thinks the two would have to combine, perhaps with the Deccan Traps eruptions in order to induce a global extinction event.

But the idea, which Chatterjee presented Sunday at the annual meeting of the Geological Society of America in Portland, Ore., has been met with deep skepticism.

"There is no need to call on Deccan or Shiva to extend the trauma of the Cretaceous-Tertiary extinction," Steven D'Hondt of the University of Rhode Island said. "We can explain it in the context of the Chicxulub impact alone."

D'hondt allowed that if Siva is ever definitively shown to be an impact crater, it will force scientists to rethink the devastation of 65 million years ago.

But he said, "Nobody has yet demonstrated that this feature is an impact feature."