When did the biggest meteor hit earth?

An American team found the world's biggest meteor crater almost two kilometres deepunder the Wilkes Land region of Antarctica, directly south of Australia. They say the 500-kilometre-wide crater wascaused by a meteor almost 50 kilometres wide,the size of Sydney. The meteor struck 250 million years ago and must have been the biggest explosion ever seen on the planet, far bigger than the 10-kilometre-wide meteor which hit east of Mexico 65 million years ago, wiping out the dinosaurs. The massive explosion from the impact probably created the continent of Australia, forcing it to break away from the existing land mass. Ohio State University scientists who found the crater said the massive Antarctic crater could explain the global extinction in the Permian-Triassic period when all animal life on Earth died out, clearing the way for the dinosaurs.