Ray burst is extinction suspect

BBC NEWS: "A huge cosmic explosion could have caused a mass extinction on Earth 450 million years ago, according to an analysis by scientists in the US. A gamma ray burst could have caused the Ordovician extinction, killing 60% of marine invertebrates at a time when life was largely confined to the sea. These cosmic blasts are the most powerful explosions in the Universe. The scientists think a 10-second burst near Earth could deplete up to half of the planet's ozone layer."