The Moon Assembled from a Swarm of Earth's Fragments express
When countless asteroids pummeled the young Earth, they tore chunks from its mantle. These fragments spiraled in a cosmic disk around the planet and, like a snowball in a blizzard, fused into the Moon.
The same scenario applies to Pluto's moon Charon and hundreds of binary asteroids in the Solar System. Importantly, fragments moving in the same direction as the disk's rotation stayed in orbit and contributed to growth, while those coming the opposite way fell back. Thus, some material destined for the Moon scattered over Earth: we walk on rocks that once traveled through space.
The Moon is iron-poor, which long didn't fit the single-impact hypothesis: such a collision would have mixed crust and mantle material, enriching the satellite. The new multi-impact model naturally solves this puzzle.