IN THE BEGINNING
Over the last century and a quarter, three theories developed about where the moon came from. The first revolutionary idea in 1878 was from George Darwin, son of the famous evolutionist. He surmised the earth had whirled itself into a frenzy early on, and ended up spinning off a chunk into space. (There are some claims that the chunk was originally in the major depression now known as the Pacific Ocean).
American astronomer Thomas Jefferson Jackson See announced in 1909 that the moon was a wandering planet, snared by the earth’s atmosphere. Astronomer Eduoard Roche couldn’t see See’s point. He figured that the earth and moon had formed at roughly the same time, from the same materials that formed all the planets in our solar system. The trio of theories became known as the “Big Three”, or Daughter: fission, Spouse: capture, and Sister: coaccretion. The problem in accepting any of them, was that theory couldn’t hold up to scientific reasoning.
Fission fell down on the job, because the earth would have needed a lightning fast rotational speed. Plus, the Pacific Ocean basin is less than 70 million years old. Capture also escapes credibility, when you consider how unlikely it is that a planet would just mosey over and dance around earth instead of slamming into it. Not to mention the similarities in oxygen-isotopes, which indicate that the two birthed around the same time, if not from the same “parents”. Coaccretion coalesced a lot of objections. The earth’s core comprises 30% of its mass compared to the moon’s 3%. The earth contains iron, the moon does not. Lunar samples indicate much of it may have once been molten, where there is no proof the Earth ever got that hot under the crust.
Enter…the Big Whack. Not quite the Big Bang theory, but just as interesting. The initial idea arose from the ashes of tests that disproved the other three theories. Something… a large celestial body, whacked Earth hard enough to blast off a considerable portion of its mantle into space, coming apart at the seams during the duet. The resulting blend of material eventually drifted together and formed the moon. But wait! Scientific studies in the mid 90s estimated that the size of the impactor would have to be roughly 2-3 times that of Mars, which would send Earth into a hyper fast rotation. Enter another Whacker, a second impact, which slowed Earth’s rotation back down.
While the Big Whack is not perfect in all aspects, it can moon the other three for a reasonable hypothesis.