Formation of the Moon:

1. collision between the proto-Earth and Theia. Both bodies were large enough to have differentiated into core, mantle and primary crust as a result of accretionary heating.
2. the cores of the two bodies have combined and the two mantles mixed, while some material was fragmented and vapourised and scattered into orbit around Earth.
3. the debris accreted under its own gravity to form the Moon. The heat of accretion resulted in wholesale lunar melting.
4. the Moon then cooled and differentiated into mantle, primary crust and (possibly) small core.
5. Moon and Earth were subject to further meteorite bombardment and the formation of large craters. Some of the impact were large enough to initiate melting of the lunar mantle, flooding the larger impact structures with basalt and forming the lunar maria.