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It is often stated that there are three types of theory concerning the origin of the earth-moon system. I feel that there are serious objections to each of them. They are; (1) Formation of the moon by fission of the earth. This idea has been attractive in the past because of the low density of the moon, which suggests that the moon might be made out of the terrestrial mantle material. However, we now know that the moon is also very much more depleted in the more volatile mantle elements than is the earth, and in my view this would be difficult to reconcile with such a mechanism.