This isn't 'the place the moon hit', it's material from the colliding object (Theia) that has been added to the Earth's mantle. The mantle convects, and this m

This isn't 'the place the moon hit', it's material from the colliding object (Theia) that has been added to the Earth's mantle. The mantle convects, and this material is a little more dense, and has pooled up at the bottom of the mantle, but because the mantle convects (the material circulates) there is no real reason to believe that these bodies are at the location of collision, especially considering that much of the mantle (and the parts of Theia that stayed behind) would have been reduced to flying bits of lava in orbit around the core, before coalescing.