Violent supernovae 'triggered at least two Earth extinctions'

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 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.