The new computer model shows that a gamma-ray burst aimed at Earth could deplete the ozone layer, cause acid rain, and initiate a round of global cooling from as far as 6,500 light-years away.

Such a disaster may have been responsible for the mass die-off of 70 percent of the marine creatures that thrived during the Ordovician period (488 to 443 million years ago), suggests study leader Brian Thomas, an astrophysicist at Washburn University in Kansas.