What if an asteroid hits planet Earth?

What would happen if an 8-mile wide asteroid was on a collision course with planet Earth?

65 million years ago an asteroid hit the Earth and wiped out the dinosaurs, but no one has ever known where the asteroid came from or how it killed off nearly three quarters of all life on Earth. This Naked Science episode uncovers alarming new evidence that the dinosaurs were doomed 100 million years before this catastrophic event. Following a group of maverick scientists, Incinerator Earth reveals what really happened; how life on Earth nearly came to an end; and what might happen if an 8-mile-diameter asteroid struck us again.