LAWRENCE, Kan., April 6 (UPI) -- U.S. scientists said a mass extinction on Earth hundreds of millions of years ago could have been triggered by a star explosion called a gamma-ray burst.
Scientists at NASA and the University of Kansas said they do not have direct evidence that such a burst activated the ancient extinction, but they have been able to assemble a persuasive case based on computer modeling.
They calculated that gamma-ray radiation from a relatively nearby star explosion, hitting Earth for only 10 seconds, could deplete up to half of the atmosphere's protective ozone layer, with recovery from the event taking at least five years.
With the ozone layer damaged, ultraviolet radiation from the sun could kill much of the life on land and near the surface of oceans and lakes, and disrupt the food chain, the scientists said.
Gamma-ray bursts in the Milky Way galaxy are rare, but the scientists estimated at least one has hit Earth over the past billion years. A massive extinction event, called the Ordovician extinction, struck the planet about 250 million years ago.
