At least two mass extinction events in Earth's history were likely caused by the "devastating" effects of nearby supernova explosions, a new study suggests. Researchers at Keele University say these super-powerful blasts – caused by the death of a massive star – may have previously stripped our planet's atmosphere of its ozone, sparked acid rain and exposed life to harmful ultraviolet radiation from the Sun. They believe a supernova explosion close to Earth could be to blame for both the late Devonian and Ordovician extinction events, which occurred 372 and 445 million years ago respectively.