Is there geological evidence that the moon once collided with the Earth?

Question

I've seen models in astronomy that show how the Earth-Moon system must have come together after a collision. However, I have not heard whether there is any actual physical evidence on Earth that points to a prior collision. Is there geological (or other physical) evidence here on Earth that confirms the moon originated from a collision on Earth? If so what is that evidence?

Answer 1

There is no evidence on Earth that I am aware of. I doubt there is, because the collision occurred when Earth was a magma ocean-- aka there is no physical evidence of an impact because there was no land to record that impact! The collision was akin to throwing a golf ball at silly putty (or better yet, a pile of a non-newtonian fluid!).

But, we know the moon came from the earth (mostly) because of isotopic ratios. The oxygen isotope ratio of rocks on the moon is the same (or extremely similar, within 4ppm difference) as the oxygen isotope ratio of earth. Other isotopes, such as zinc and titanium also support the impact hypothesis.