Dino-killing rock more deadly than previously thought

Thursday, January 22, 2009

The theory that pins the Chicxulub asteroid impact to the extinction of dinosaurs 65 million years ago may need some revision.

It may now need to account for the fact that the impact in question made a bigger splash than scientists previously thought, according to a new study.

University of Texas research scientist Sean Gulick and colleagues analysed the most detailed three-dimensional seismic images to date and found that the crater site was in deeper water than earlier studies suggest.

The particular location of the site and this minor detail would have carried grave implications in what's been dubbed the "KT Extinction Event" - an event largely thought to have killed off about 70 per cent of life on Earth.

A worldwide extinction

By landing in deeper water, the impact would have released 6.5 times more water vapour into our atmosphere than previously thought. The impact site also contained sulphur-rich sediments called evaporates.

According to Gulick, these factors combined would have made the impact deadlier in two ways: by altering the climate (sulphate aerosols in the upper atmosphere have a cooling effect) and by generating acid rain, which would have made the oceans more acidic.

This modification of the extinction theory would account for why reef and surface dwelling ocean creatures were affected along with large vertebrates on land and in the sea. There is also some evidence that marine organisms more resistant to a range of pH levels survived while those that were more sensitive did not.

Gulick acknowledges, though, that the mass extinction event was probably not caused by a single mechanism. Rather, it was the combination of several environmental changes on different time scales, in different locations that led to the extinction of some of the largest creatures our Earth has ever known.

Details of the study appear in the 2008 edition of the journal Nature Geosciences.


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