Asteroids crashing into Earth have virtually wiped out life not once but at least twice, scientists have reported. An asteroid or comet roughly the same size as the one that wiped out the dinosaurs 65 million years ago did even worse damage 250 million years ago, experts found in a report published in Friday's issue of the journal Science. The evidence comes from space gases trapped in little carbon spheres called Buckyballs in ancient layers of sediment. They show the Permian extinction event, during which most species on the planet disappeared, started with a cosmic collision. "The impact ... releases an amount of energy that is basically about 1 million times the largest earthquake recorded during the last century," Robert Poreda, associate professor of earth and environmental sciences at the University of Rochester in New York, who worked on the study, is quoted by Reuters as saying in a statement. The comet or asteroid would have to have been 4 to 8 miles (6.5 to 13 kms) across. The jolt roused volcanoes, which buried huge areas in lava and sent up ash to join the dust from the explosion to plunge the world into centuries of unnatural dark and cold. Trilobites - strange, cockroach-like creatures that once ruled the planet - died out completely, all 15,000 species of them. Ninety percent of all marine creatures and 70 percent of land vertebrates went extinct. The asteroid which wiped out the trilobites was just about the size of an asteroid that left a giant crater on Mexico's Yucatan Peninsula 65 million years ago and wiped out the dinosaurs.