Okay grabbed this from another thread where it was asked if the current idea of the Moon coming from a collision between Earth and a Mars sized planet was reasonble.
This brought a small question to mind. IIRC one of the reasons we are sure of the Moon missions is due to the unique features of the Moon rocks, especially that they are anhydrus, or were formed without the presence of water. Earth rocks all have evidence of having been formed in water whereas Moon rocks apparently don't have any evidence of such. If the moon was once part of Earth though, shouldn't it have some evidence in its rocks of water?