Replies

""The evidence points to the collision theory. First, the Moon does not have an iron core. This pretty much rules out that it coalesced from the same cloud of debris that the Earth did."" (RadioAstronomer)

"That evidence would also support the capture theory. Moreover, all iron on Earth and no iron on the Moon makes for a pretty bizarre collision theory. Capture makes more sense." (Southack)

The collision theory is well accepted now, for many reasons; among them: the reason for the lack of iron on the moon.

The collision of a small planet and Earth was not a direct hit. (A direct hit is statistically less likely than a glancing blow). The Earth remained largely intact. Its mantle was blown away in part, into Earth orbit. The material that is now the moon came from this debris and the debris of the incoming body (low in iron). This scenario is consistent with the similarities in Earth's and moon's geology, and also the differences between the two.

The Earth's inner and outer core (location of most of the iron in Earth) were not affected, and did not contribute to the mass of the moon... thus, did not place Earth's iron into the moon's core.

The Capture theory also runs into problems with the capture itself. Earth-moon mass ratio is unlike that of a planet much more massive than a much smaller moon... (a huge mass ratio of planet-to-moon - like Mars and Phobos, a possible example of moon-capture). Earth and moon are more nearly matched in mass, making a collision-free capture much less likely.