Dinosaur whodunit: Is Shiva crater the missing link?

It could be the plot of a mega disaster movie. A huge asteroid, nearly 40 km in diameter, comes hurtling towards earth.

By Atul Sethi, TNN | Nov 08, 2009, 09.58 AM IST

It could be the plot of a mega disaster movie. A huge asteroid, nearly 40 km in diameter, comes hurtling towards earth. It strikes the planet, off the western coast of India, near Bombay High, creating a vast crater, 500 km wide. Temperatures in the area rise rapidly, reaching several thousand degrees Celsius and releasing more energy than the world��s entire nuclear arsenal. Soon enough, this energy starts devastating the atmosphere, rupturing the thin shell of air, water, soil and surface rock that nurtures and sustains life. The result is destruction and mass extinction.

The scenario above is not the figment of some scriptwriter��s imagination. Instead, it is the essence of a theory put forward by Sankar Chatterjee, a professor at Texas Tech University, to explain why dinosaurs became extinct almost 65 million years ago. Chatterjee��s hypothesis is that the crater, named Shiva, fast forwarded the extinction of dinosaurs. The jury is still out on his theory. But it renews the focus on that great unsolved mystery: Why did dinosaurs die out?

American palaeontologist Gregory Paul, who has researched dinosaurs for three decades, says, ��It continues to remain unexplained how all dinosaurs around the entire globe were lost when other animal groups including their avian descendants were not killed off.��

Dinosaurs were the dominant form of life on earth for 140 million years and suddenly disappeared sometime between the end of the Mesozoic era and the beginning of the Cenozoic era, nearly 65 million years ago. Scientists refer to this period as the K-T Boundary.

How Did They Die?
Two major theories have sought to explain dinosaur��s demise: one, meteorite impact; and the second,�� volcanic activity
Before Chatterjee��s contention, the consensus among scientists supporting the meteorite theory was that the Chicxulub Crater, buried under the Yucatan peninsula in Mexico, wiped out many plant and animal groups, including dinosaurs. But Chatterjee has a different take on the matter. According to him, Chicxulub was only the trailer.

The real show began with the arrival of the Shiva crater. ��Since the Shiva crater is about 500 km in diameter, it could well be the largest impact crater known on Earth. This makes it a viable candidate for the impact on the K-T boundary and the mass extinction that followed,�� he says.

Research over the past few years supports Chatterjee��s theory somewhat. According to Gerta Keller, professor of paleontology at Princeton University, the Chicxulub crater was formed 300,000 years before the KT boundary and was much smaller than originally thought. Therefore, it could not have had the immediate impact required for extinction on such a scale. ��What it could probably have done would be to start the process that led to the extinction 300,000 years later,�� she says.��

The Indian Angle
Chicxulub aided a process, which may have been nudged further forward by intense volcanic activity, especially in the Deccan Trap region of Central India. ��The volcanic activity in the region between 68 and 65 million years ago was one of the most stupendous eruptions ever witnessed on earth,�� says Ashok Sahni, geologist at Punjab University and author of the book, Dinosaurs of India.

There is evidence of the volcanic impact on the extinction of dinosaurs �� the discovery of the pelvic girdle (hip-bone) of a fairly large Titanosaurid dinosaur, found in sediments sandwiched by Deccan lava flows, at a small village, near Jabalpur.

Palaeontologists have now come around to the view that it was a combination of events that killed the dinosaurs. ��The causative reasons could be asteroids like Chicxulub as well as Deccan volcanism. These factors might have been accelerated by the impact of other asteroids that would have dealt the final blow,�� says M L Chhabra, head of Lucknow University��s department of geology.

In this context, Chatterjee��s contention that the Shiva crater provided the last nail in the dinosaurs�� coffin may be the missing piece in the jigsaw. However, some questions��still remain. Why did birds and amphibians, who are very sensitive to environmental toxins, survive the holocaust, whereas dinosaurs who apparently had good thermoregulatory abilities, perish? Till these answers are found, the mystery of the dinosaurs�� exti-nction may continue to tantalise.

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