Photos from space of some of the earth's impact craters. (h/t Thompson's Friday Ephemera.)
If I remember rightly, the Gulf of Mexico was an impact crater. A big collision. Big one in the Chesapeake, too.
But the biggest might have been the one that separated the earth from the moon. Thank God for that one. There would be little romance without it. No romance = no sex = no fun = no babies.