The Population of Impactors after the Giant Impact

After the Moon-forming impact, the Earth and Moon would have been subject to impacts by asteroids, comets, and leftovers of accretion. All are plausible sources of the impactors that produced the Late Heavy Bombardment (LHB). The LHB might have included a "Lunar Cataclysm," or cratering spike, near 3.9 Ga. A mechanism for such a cataclysm involving asteroid showers following the breakup of a large main-belt asteroid has recently been proposed. However, this model, while reasonable, requires a massive main belt or unlikely breakup event.