A recently discovered layer of glassy fragments could only have been made by a meteor slamming into Earth and helps prove such an impact nearly wiped out life on the planet 250 million years ago, scientists said. They outlined what they believe is an ancient crater left by the impact off the coast of what is now Australia. "What we found is a melt sheet which is defining the top of this very large feature out in the ocean," geologist Luann Becker of the University of California Santa Barbara told a news conference.