Since science has declared the Earth the sole parent of the Moon, lets indulge in conjecture. Did the Earth undergo sufficient expansion under near zero gravity conditions that would have allowed a large part of herself to become independent and then slowly or suddenly regain gravity to solidify the now two separate parts. That is not my favorite theory. The one I prefer is this: As O Manuel suggests the sun and I propose most planets have an iron core which when heated overmuch can produce a 'birth' of a planetary body. Casseopia A shows clearly in Chandra pics that the ordered elements show this birth direct from the core.