The Shiva Impact & Extinction of the Dinosaurs

It seems that there is growing evidence that the dinosaurs and most their contemporaries were not wiped out by the famed Chicxulub meteor impact, according to a paleontologist who says multiple meteor impacts, massive volcanism in India, and climate changes culminated in the end of the Cretaceous Period and the Age of Reptiles.

The Chicxulub impact -a ringed formation 120 miles wide and 30 miles deep under Mexico's Yucatan Peninsula discovered in 1990- may, in fact, have been the lesser and earlier of a series of meteors and volcanic eruptions that pounded life on Earth for more than 500,000 years, say Princeton University paleontologist Gerta Keller.

A final, much larger and still unidentified impact 65.5 million years ago -known as the Shiva Impact, named after the Hindu god of death and destruction- appears to have been the last straw, exterminating two thirds of all species in one of the largest mass extinction events in the history of life.

It's the Shiva impact – not Chicxulub – which left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles.

"The Chicxulub impact could not have caused the mass extinction," says Princeton University paleontologist Gerta Keller, "because this impact predates the mass extinction and apparently didn't cause any extinctions."

Marine sediments drilled from the Chicxulub crater itself, as well as from a site in Texas along the Brazos River, and from outcrops in northeastern Mexico reveal that Chicxulub hit Earth 300,000 years before the mass extinction. Small marine animal microfossils were left virtually unscathed, says Keller.

"In all these localities we can analyze the marine microfossils in the sediments directly above and below the Chicxulub impact layer and cannot find any significant biotic effect," said Keller. "We cannot attribute any specific extinctions to this impact." No one has ever published this critical survival story before, she said. Keller's research was funded by the National Science Foundation.

The story that seems to be taking shape is that Chicxulub, though violent, actually conspired with the prolonged and gigantic eruptions of the Deccan Flood Basalts in India, as well as with climate change, to nudge species towards the brink. Their fate was sealed with a final, second large impact.

The Deccan volcanism did the nudging by releasing vast amount of greenhouse gases into the atmosphere over a period of more than a million years leading up tothe mass extinction. By the time Chicxulub struck, the oceans were already 3-4 degrees warmer, even at the bottom, Keller says.

"On land it must have been 7-8 degrees warmer," says Keller. "This greenhouse warming is well documented. The temperature rise was rapid, over about 20,000 years, and it stayed warm for about 100,000 years, then cooled back to normal well before the mass extinction."

Marine species at the time suffered from the heat. Most adapted to the stress conditions by dwarfing, growing less than half their normal size and reproducing rapidly with many offspring to increase the chances for survival. The Chicxulub impact coincided with this time. By the time climate cooled back to normal, most tropical species were on the brink of extinction.

So where's the Shiva Impact crater, a question pondered by Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany.

"I wish I knew," said Keller. "There is some evidence that it may have hit in India, where a crater of about 500 kilometers in diameter is estimated and named Shiva by paleontologist Sankar Chatterjee from the Museum of Texas Tech University in Lubbock.

Adopted from a press release from the Geological Society of America/American Association for the Advancement of Science.

Posted by Casey Kazan.