What Happens When Something Big Hits the Earth?

Professor O'Mara says this kind of thing is unpredictable, meaning there's no way to figure out exactly when it might happen. We know that it's happened before and we've seen pieces of a comet hit Jupiter only a couple decades ago. But we don't really know when the next type of thing or if the nexttype of thing is going to hit the Earth. So that one's a little bit wishy-washy in terms of when. But we do know what kind of things it can do depending on how big it is and what it does to the Earth.