Collisions and impact processes have been important throughout the history of the solar system, including that of the Earth. Small bodies in the early solar system, the planetesimals, grew through collisions, ultimately forming the planets. The Earth started growing ca. 4.56 Ga in this way. Its early history was dominated by violent impacts and collisions, of which we only have circumstantial evidence. The Earth was still growing and had reached ∼70%–80% of its present mass when at ca. 4.5 Ga a Mars-sized protoplanet collided with Earth, leading to the formation of the moon—at least according to the currently most popular...