That big asteroid isn't going to hit us. They say now that it'll come within 100,000 miles though, which is pretty close. But pretty close is far enough. It isn't big enough to do that much damage anyway, even if it did hit. Localized damage, maybe a little more if it hit water.

Incidentally, rocks that hit water are far more dangerous to the human race than those that hit land, oddly enough. A big rock hitting land might wipe out a state-sized area. A big rock hitting water would vaporize monumental amounts of water and cover the earth with clouds for years, cause tsunamis and tidal waves and wipe out cities along whatever coasts are near. For a good fictional account of a big rock hitting the earth, and the aftermath, I recommend 'Lucifer's Hammer' (by Larry Niven and Jerry Pournelle). Great book!