If some TV documentary is to be believed, the moon was once about 1/3 the distance away, causing mountain-high tides that swept across entire continents, dissolving out the salt from the land into the ocean.
OK, I can buy that. What I don’t buy is the idea that some random Mars-sized body hit the earth to create the moon. Without an explanation of the origin and fate of that body, it just sounds like crazy Velikovsky again. (He’s the guy who tried to misuse several sciences to try to prove that Old Testament miracles were literally true.)