The city-size rock that impacted Earth sixty-five million years ago, in what is now Mexico's Yucatán Peninsula at a site known as Chicxulub, may not have been the main cause of the great extinction event that wiped out the dinosaurs and as much as 80 percent of the rest of life on the planet.
Instead, a 25-mile-wide meteorite, as much as five times the size of the one that struck Chicxulub, could have slammed into Earth where India is today, vaporizing the planet's crust and leaving the largest multi-ringed crater the world has ever seen.
Impact illustration courtesy NASA
Texas Tech University scientists think they have pieced together the geological evidence for this impact, and they will present their theory to the annual general meeting of the Geological Society of America (GSA), in Portland, oregon, this coming weekend.
"A mysterious basin off the coast of India could be the largest, multi-ringed impact crater the world has ever seen. And if a new study is right, it may have been responsible for killing the dinosaurs off 65 million years ago," GSA said in a statement about the research, released today.
"Sankar Chatterjee of Texas Tech University and a team of researchers took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and gas resources. Some complex craters are among the most productive hydrocarbon sites on the planet," GSA said.
Chatterjee will present the research at the GSA meeting on Sunday.
Largest crater on the planet
"If we are right, this is the largest crater known on our planet," Chatterjee said. "A bolide of this size, perhaps 40 kilometers (25 miles) in diameter, creates its own tectonics."
By contrast, the object that struck the Yucatan Peninsula, and is commonly thought to have killed the dinosaurs, was between 5 and 6 miles wide, GSA said.
"It's hard to imagine such a cataclysm. But if the team is right, the Shiva impact vaporized Earth's crust at the point of collision, leaving nothing but ultra-hot mantle material to well up in its place.
"It is likely that the impact enhanced the nearby Deccan Traps volcanic eruptions that covered much of western India. What's more, the impact broke the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa."
Dramatic geological evidence
The geological evidence is dramatic, GSA added.
Three-dimensional reconstruction of the submerged Shiva crater, western shelf of India, from different cross-sectional and geophysical data. The overlying 4.3-mile-thick Cenozoic strata and water column were removed to show the structure of the crater.
Image courtesy of Geological Society Of America
"Shiva's outer rim forms a rough, faulted ring some 500 kilometers [310 miles] in diameter, encircling the central peak, known as the Bombay High, which would be 3 miles tall from the ocean floor (about the height of Mount McKinley).
"Most of the crater lies submerged on India's continental shelf, but where it does come ashore it is marked by tall cliffs, active faults and hot springs. The impact appears to have sheared or destroyed much of the 30-mile-thick granite layer in the western coast of India."
Illustration courtesy of NASA
Two large impacts such as Shiva and Chicxulub in quick succession, in concert with Deccan eruptions (a series of monumental volcanic eruptions in India that some scientists believe may have been the real culprit that killed the dinosaurs 65 million years ago), would have devastating effects globally, Chatterjee and colleagues say in the abstract to their presentation.
That, in turn, could have caused the "climatic and environmental catastrophes that wiped out dinosaurs and many other organisms" at the time of the mass extinction.
The team hopes to go India later this year to examine rocks drill from the center of the putative crater for clues that would prove the strange basin was formed by a gigantic impact.
"Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly," Chatterjee said. "Asteroids are rich in iridium, and such anomalies are thought of as the fingerprint of an impact."
Related National Geographic News stories:
Yucatan Asteroid Didn't Kill Dinosaurs, Study Says
A controversial new study contends that a second, as yet unidentified asteroid impact must have caused the mass extinction popularly attributed to the Chicxulub asteroid.
"Dinosaur Killer" Asteroid Only One Part of New Quadruple-Whammy Theory
The dinosaurs were killed not by a lone asteroid strike but by the quadruple whammy of global climate change, massive volcanism, and not one but two gigantic collisions.
Asteroid Rained Glass Over Entire Earth, Scientists Say
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