WASHINGTON (AFP) - A meteor's roaring crash into Antarctica -- larger and earlier than the impact that killed the dinosaurs -- caused the biggest mass extinction in Earth's history and likely spawned the Australian continent, scientists said. Ohio State University scientists said the 483-kilometer-wide (300-mile-wide) crater is now hidden more than 1.6 kilometers (one mile) beneath the East Antarctic Ice Sheet. "Gravity measurements that reveal its existence suggest that it could date back about 250 million years -- the time of the Permian-Triassic extinction, when almost all animal life on Earth died out," the university said in a statement Thursday....