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Were the dinosaurs fried by ultraviolet light?
BY NEIL ENGLISH
ASTRONOMY NOW

Posted: May 3, 2000

  Impact
An artist's concept of an asteroid hitting the Earth. Photo: NASA
 
Over the past few decades, the rise and fall of the dinosaurs has captured the imagination of the public and the scientific community alike. While it is clear that the impact of a large asteroid straddling the coastline of what is the Yukatan peninsula in Mexico some 65 million years ago, may have wiped out these magnificent reptiles, the debate still rages as to precisely how they met their demise.

Many scenarios have been suggested, including a kind of nuclear winter in which enormous quantities of dust were ejected into the stratosphere, circling the globe and blotting out sunlight for weeks or months. But not everyone agrees that such a successful biological lineage as the dinosaurs could have been obliterated in this way.

Now, two American scientists - Charles Cockell of NASA's Ames Research Centre In California, and Andrew Blaustein of Oregon State University, have worked out the events that occasioned themselves immediately after the KT impact.

In a recent paper communicated in Ecology Letters, they explain that the levels of nitrogen and sulphur oxides produced during the impact event would have all but destroyed the ozone layer, thereby doubling the levels of lethal UV radiation incident on the earth's surface. This deluge of ionising radiation would have put additional stresses on the biosphere already stretched to the extreme by the impact.

What is even more remarkable though, is that significant sulphate deposits are only found over 1 percent of the earth's surface, rendering the KT extinction event particularly lethal for the dinosaurs, but not for our kind - the small, furry, milk-suckling mammals.

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