Last night me and my roommate were watching a show on the History Channel that got us into a two-hour discussion about the viability of a meteor hitting the moon sometime around 5000 B.C. and causing global tidal shifts/waves that created the varying stories from different religions about the "great flood". I thought that anything big enough to cause that much instability would have left a crack in the moon, but he came up with the idea of a meteor merely passing closely to the moon and affecting its gravity/rotation for a short time.