Asteriod 'destroyed life 250m years ago'

A giant comet or asteroid hit the Earth 250 million years ago and triggered the biggest mass extinction in history. The disaster was even more catastrophic than the impact which is thought to have ended the reign of the dinosaurs 65 million years ago. It resulted in almost all life - 90% of all marine species and 70% of land vertebrates being wiped out. Professor Robert Poreda of the University of Rochester in New York is one of the scientists researching the findings: