One piece of evidence that suggests the Earth and the moon may have once been in the same place is the similarity in isotopic compositions of certain elements found in both bodies. Specifically, the oxygen isotopic compositions of Earth and moon rocks are nearly identical, indicating that they formed from the same material. This supports the idea that the moon formed from material ejected from Earth as a result of a giant impact. Additionally, the moon has a much smaller iron core compared to Earth, which is consistent with the giant impact theory, as the force of the impact would have vaporized much of the material from Earth's core.
