While initial reports point towards it coming from space, I have managed to traced the origin back to the big bang. That's right, it was rigged to happen from the start.
jsiepkes
It was a bug meteor from the asteroid ring around Klendathu.
chiefalchemist
Not to get off topic but (some myth busting is in order) the updated theory is excessive volcanic activity had already been killing off the dinosaurs. The asteroid wasn't the primary killer, but more like the last straw.