Doomsday Rocks from Space

What happened to the dinosaurs? Scientific evidence suggests that a giant asteroid crashed into Earth 65 million years ago, killing off the dinosaurs. This doomsday rock could have changed the course of life on Earth. What are the chances of a doomsday rock striking Earth today, destroying the world as we know it? Author Margaret Poynter investigates the science of doomsday rocks and what danger they are to us.