I am become Death, destroyer of worlds
Oct 22nd 2009
From The Economist print edition
The story of how the dinosaurs disappeared is getting more and more complicated
EVERYONE knows that the dinosaurs were exterminated when an asteroid hit what is now Mexico about 65m years ago. The crater is there. It is 180km (110 miles) in diameter. It was formed in a 100m-megatonne explosion by an object about 10km across. The ejecta from the impact are found all over the world. The potassium-argon radioactive dating method shows the crater was created within a gnat’s whisker of the extinction. Calculations suggest that the “nuclear winter” from the impact would have lasted years. Plants would have stopped photosynthesising. Animals would have starved to death. Case closed.
Science Photo - NASA
Well, it now seems possible that everyone was wrong. 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.
Double whammy
In truth, agreement on the cause of the mass extinction at the end of the Cretaceous (when not only the dinosaurs, but also a host of other species died) has never been as cut and dried among palaeontologists as it may have appeared to the public. One confounding factor is that the late Cretaceous was also a period of great volcanic activity. In India, which was then an island continent like Australia is today (it did not collide with Asia until 50m years ago), huge eruptions created fields of basalt called the Deccan Traps. Before the discovery of Chicxulub, the climate-changing effects of these eruptions had been put forward as an explanation for the death of the dinosaurs. After its discovery, some argued that even if the eruptions did not cause the extinction, they weakened the biosphere and made it particularly vulnerable to the Chicxulub hammer-blow.
...
Read more here/Leia mais aqui.
