Well, the asteroid (actually a comet) that killed the dinos wast estimated to be somewhere between 11 and 81 kilometres in diameter, which is way bigger than this asteroid. And even that impact didn't destroy the earth. To actually destroy the earth (as in, crack the crust, melt the surface, and generally render the place sterile), you'd probably need something the size of a small moon. There are no such objects in the solar system that we wouldn't see coming a long time in advance.