> but this one was 100% identical to Earth's crust? Given the size of this impact, the crust[1] didn't really survive. Most of the mantle material ended up va

> but this one was 100% identical to Earth's crust? Given the size of this impact, the crust[1] didn't really survive. Most of the mantle material ended up vaporized and either falling back down or coalescing onto a single fragment, becoming the moon. It was a collision "of" the planet, not "on" the planet. [1] Which in any case wouldn't have survived this long anyway. The differentiation process that produces the crust we're standing on takes billions of years. There aren't any surface rocks that old, and wouldn't be even if the collision hadn't happened.