The book Darwin’s Ghost (by Ateve Jones) tells us that ... “The Moon flew off its parent after a giant impact. Because it stayed small, cold and undisturbed it gives a better picture of the past than does its parent. A guick trip by the Apollo 11 mission was enough to date it. The Earth’s turmoil makes it harder to trace its own origin. Its oldest rocks, found in Greenland and Western Australia, are just under four billion years old.”
Pardon me for the typo. Darwin’s Ghost was written by Steve Jones.
The radiometric dating of a moon rock brought back by Apollo 17 showed a date in excess of the generally accepted age of the Moon (by over 100 million years). And while I’m normally a big fan of impact, imho the origin of the Moon is not an impact of a Mars-sized object with the proto-Earth:
When the Days Were Shorter
http://www.freerepublic.com/focus/chat/1234919/posts