Supernova fingered in Devian mass extinction

359 million years ago Earth suffered one of its worst extinction events. The boundary of the Permian and Triassic geological periods marked the demise of around 90% of marine species and 70% of land species. A team of researchers at the University of Illinois think that it might have been caused by a series of supernova explosions no more than 35 light years away. The last mass extinction event happened about 65 million years ago. It finished the dinosaurs and began the rule of mammals. The smoking gun for researchers is the fact that fossils of plants from the K/T extinction event show signs of excess UV exposure. The intense radiation from a close enough supernova blast is capable of stripping away the ozone layer. Plutonium-244 is an element that isn’t naturally produced on Earth, so the only way for it to exist in a layer of sediment is for it to have been put there as the shock-wave of a supernova.