Yasmin Jeffery and Marc Fennell for Stuff the British Stole Billions of years ago, well before the origin of Earth, a rock was floating through space. It once formed part of a living planet. At some nebulous point in time, that planet died. It's hard to say how or why that happened, but in its afterlife, the rock was given a new name: asteroid. It likely would have continued travelling undisturbed through the furthest reaches of the universe. Except it was hit by something.