Distant star explosions could have wiped out life on Earth twice

Most people know the theory that an asteroid smashed into Earth — hitting what is now the Yucatán Peninsula — and killed off many of the dinosaurs about 66 million years ago. But that was not the only mass extinction for the planet — just the most well-known. Scientists believe at least five mass extinctions have occurred in the past 500 million years, and not all of them were caused by menacing space rocks. Perhaps two of them, one 372 million years ago and another 445 million years ago, were ice ages. A new study, based on a census of stars in the Milky Way, suggests those periods of severely cold climates may have begun with stars dying light-years away. "If a massive star were to explode as a supernova close to the Earth, the results would be devastating for life on Earth," said Nick Wright, an astrophysicist at Keele University in the United Kingdom, in a statement. "This research suggests that this may have already happened." SEE ALSO: Hubble sees mini galaxies surrounding Andromeda are pretty wild A fossil of a type of brachiopod, Floweria chemungensis, went extinct in the late Devonian period. Credit: Andrew Bush / National Science Foundation Previous research has yet to determine the cause for either the late Devonian or Ordovician mass extinctions, which occurred 372 and 445 million years ago, respectively. The Ordovician extinction is thought to have killed off about 60 percent of the invertebrate sea creatures at a time when most of Earth's species lived in the ocean; the late Devonian event eliminated 70 percent of all creatures and influenced sweeping changes in the kinds of fish that survived. Scientists have suspected these ice ages followed damage to the ozone layer. Crucially, the team working on the census says supernovas could have triggered the catastrophic changes in Earth's protective atmosphere. The rate of supernovas near Earth is consistent with the timing of both mass extinctions. The team's findings appear in the Monthly Notices of the Ro