SCI/TECH: Did gamma rays doom ancient life?

Not a giant meteorite, but gamma rays from an exploded supernova are now believed to be the cause of the the second-largest extinction in the Earth's history, 440 million years ago...

Atlanta ? The second-largest extinction in the Earth's history, the killing of two-thirds of all species, may have been caused by ultraviolet radiation from the sun after gamma rays destroyed the ozone layer.

Astronomers are proposing that a supernova exploded within 10,000 light-years of Earth, destroying the chemistry of the atmosphere and allowing the sun's ultraviolet rays to cook fragile, unprotected life forms.

All this happened about 440 million years ago and led to the Ordovician extinction, the second most severe of the planet's five great periods of extinction.

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CNN.com article

[Edited on 8-1-2004 by Zion Mainframe]