Thursday, October 22, 2009

The Dinosaurs were tougher than we thought - Shiva

We knew the dinosaurs were tough. Turns out it may have taken a hell of a lot to kill the non-Avian dinosaurs ...
Mass extinctions: I am become Death, destroyer of worlds | The Economist

... The Chicxulub crater, as it is known, may have been a mere aperitif. According to Sankar Chatterjee of Texas Tech University, the main course was served later. Dr Chatterjee has found a bigger crater—much bigger—in India. His is 500km across. The explosion that caused it may have been 100 times the size of the one that created Chicxulub. He calls it Shiva, after the Indian deity of destruction.

Dr Chatterjee presented his latest findings on Shiva to the annual meeting of the Geological Society of America in Portland, Oregon, on October 18th. He makes a compelling case, identifying an underwater mountain called Bombay High, off the coast of Mumbai, that formed right at the time of the dinosaur extinction. This mountain measures five kilometres from sea bed to peak, and is surrounded by Shiva’s crater rim. Dr Chatterjee’s analysis shows that it formed from a sudden upwelling of magma that destroyed the Earth’s crust in the area and pushed the mountain upwards in a hurry. He argues that no force other than the rebound from an impact could have produced this kind of vertical uplift so quickly. And the blow that caused it would surely have been powerful enough to smash ecosystems around the world...

... Extensive dating research at Chicxulub, however, now suggests that the object which created that crater actually struck 300,000 years earlier than the dinosaur extinction, meaning there really should be two ejecta layers. That there are not could be explained by the fact that the accumulation of sediment in most rocks is so slow that the two layers are, in effect, superimposed. Alternatively, it could be that no one has been looking for two layers, so they have not seen the double signature or have ignored its significance. Indeed, two iridium layers have been found in some places. Anjar, an Indian town north of the impact site, is one. That is leading Dr Chatterjee to suggest that the two big impacts did take place at different times.

The picture that is emerging, then, is of a strange set of coincidences. First, two of the biggest impacts in history happened within 300,000 years of each other—a geological eyeblink. Second, they coincided with one of the largest periods of vulcanicity in the past billion years. Third, one of them just happened to strike where these volcanoes were active. Or, to put it another way, what really killed the dinosaurs was a string of the most atrocious bad luck.
Dinosaurs were even tougher than we'd imagined Bayesian reasoning suggests the earth has also been more dangerous than we've thought.
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