Radiation from an exploding star may have been the cause of death for 95 percent of the species on Earth 225 million years ago, according to research published today in the Proceedings of the National Academy of Science. The study's authors theorize that an explosion as far as 185 trillion miles away could have eroded the earth's protective layer, exposing plant life to deadly ultraviolet radiation and thus disrupting the food chain. A supernova has long been a suspect in the planet's most severe episode of mass extinction, but today's evidence is the first to connect an exploding star with destruction of the ozone. TIME science writer Michael Lemonick explains, "This is a theory that has been around, but nobody has had a good explanation until now. It looks as if the researchers have done the calculations and come up with a plausible theory for what happened."