Ten-Second Gamma Ray Burst Could Cause Mass Extinctions
Scientists at NASA and the University of Kansas have concluded that such a blast, caused by the explosion of a nearby star (within 6,000 light years), could destroy half of the earth's ozone layer, letting in ultraviolet rays that would kill most life on land and near the surfaces of oceans and lakes.
A gamma-ray burst may have been the cause of the Ordovician extinction 450 million years ago. Long before the dinosaurs, life during that period was largely confined to the seas... and 60% of that life was wiped out in that event. Additionally, the burst likely caused the earth's temperature to drop, ushering in an ice age.