How the Moon Was Made
There is presently only one generally accepted explanation for the Moon coming to be what it is and where it is. This is known as the Giant Impact theory. It is suggested that the early Earth was struck by a large, Mars sized planet. As a result matter was forced off the Earth and into orbit. This material eventually came together to form the Moon.
The Giant Impact theory seems attractive at first because it appears to answer a few questions. For example: we know for sure that the Earth and the Moon originated in the same part of space, but the Moon is very light in mass compared to the Earth, even allowing for its smaller size. It is 'made from' the Earth, but only from Earth's lighter, surface material. The Giant Impact theory suggests that in the collision only this lighter material was ejected into space and so formed the Moon. However, the Giant Impact theory has several shortcomings. The impact suggested would have set the Earth spinning wildly - much too fast to have slowed down as much as it has, even allowing for the Moon. This means that for the Giant Impact theory to be credible there had to be another impact from another huge body, this time coming from the opposite direction, in order to slow the spin of the Earth. This is known as Giant Impact 2 but it isn't talked about much because it's so unlikely it's virtually impossible. Also there is no trace of the planet that is supposed have impacted the Earth in the first place, which should show up as different oxygen isotopes in rocks. Another Possibility
No other explanation for the Moon's existence is presently put forward by science. It used to be thought that the Moon could be a captured asteroid but for all sorts of reasons this is now discounted. The only alternative explanation is the one we put forward: namely that the Moon was artifically created from material deliberately removed from the surface of the infant Earth. This sounds unlikely but will make more sense later when we talk about the very specific 'size' of the Moon. Exactly 'how' sufficient material was removed from the surface of the Earth to create the Moon is discussed in detail in our book 'Who Built the Moon'.
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