A mass extinction event that struck Earth 359 million years ago still has scientists scratching their heads. Was it volcano eruptions? Meteorites? Gamma-ray bursts? A new paper looks at another possible culprit: exploding stars. Researchers at the University of Illinois argue that evidence hidden in rocks coincides with the effect of at least one supernova 65 light-years from Earth in the Late Devonian period, Futurism reports. Analyzing ancient plant spores in rocks, they found signs of severe ultraviolet light sunburn—just what you would expect from long-term ozone depletion in the atmosphere. "Large-scale volcanism and global warming can destroy the ozone layer, too, but evidence for those is inconclusive for the time interval in question," lead author Brian Fields says in a statement.
Now his team is seeking what Fields calls "the smoking guns of a nearby supernova": the radioactive isotopes samarium-146 and plutonium-244 in fossils and rocks deposited during the extinction. "Neither of these isotopes occurs naturally on Earth today, and the only way they can get here is via cosmic explosions," says co-author Zhenghai Liu. Interesting side note: The team considers multiple blasts a possibility because huge stars often exist in clusters and can detonate if triggered by a supernova in the group, Forbes notes. But Fields sees a bigger message in all this: "Life on Earth does not exist in isolation," he says. "We are citizens of a larger cosmos, and the cosmos intervenes in our lives—often imperceptibly, but sometimes ferociously." (Read more mass extinction stories.)