Tuesday, January 29, 2008

Dinosaur Killer Made Quite a Splash

via ScienceDaily, a new analysis of the Chicxulub crater off Mexico's Yucatan penninsula, shows the asteroid impact that formed it 65 million years ago landed in much deeper water than previously thought. The asteroid is thought to be the major factor in the KT Extinction event which eliminated an estimated 70% of life on Earth. The amount of water vapor released into the atmosphere from the impact is now estimated to be 6 1/2 times greater than initially theorized, and that the sediments at the impact site contained far more sulfur. Sulfur released from the site would have caused an even deadlier result in two ways - by altering climate due to the cooling effect caused by sulfate aerosols and generating acid rain.

"The greater amount of water vapor and consequent potential increase in sulfate aerosols needs to be taken into account for models of extinction mechanisms," says Sean Gulick, a research scientist at the Institute for Geophysics at The University of Texas at Austin's Jackson School of Geosciences .

An increase in acid rain might help explain why reef and surface dwelling ocean creatures were affected along with large vertebrates on land and in the sea. As it fell on the water, acid rain could have turned the oceans more acidic. There is some evidence that marine organisms more resistant to a range of pH survived while those more sensitive did not.

Gulick says the mass extinction event was probably not caused by just one mechanism, but rather a combination of environmental changes acting on different time scales, in different locations. For example, many large land animals might have been baked to death within hours or days of the impact as ejected material fell from the sky, heating the atmosphere and setting off firestorms. More gradual changes in climate and acidity might have had a larger impact in the oceans."

Gulick's original intent was to determine the asteroid's trajectory, which he hoped would lead his team to the locations where the most extreme consequences of the event would be found, but instead found that the conditions at the impact site itself had more to do with the resulting extinciton event.

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