"End of the World" - Simulation

What would happen if a meteor or comet, about the size of a small moon, hit our planet? When I was in college, I studied the question from the point of view of astronomy and physics. I've even seen a few computer simulations. I have found a great simulation on the internet. The video is in Japanese because it was made by Japanese scientists. It's good because you don't have to understand the narration to see how totally messed up we would be if something like this happened!