Late accretionary history of Earth and Moon preserved in lunar impactites

Late accretion describes the final addition of Earth's mass following Moon formation and includes a period of Late Heavy Bombardment (LHB), which occurred either as a short-lived cataclysm triggered by a late giant planet orbital instability or a declining bombardment during late accretion. Using genetically characteristic ruthenium and molybdenum isotope compositions of lunar impact-derived rocks, we show that the impactors during the LHB and the entire period of late accretion were the same type of bodies and that they originated in the terrestrial planet region. Because a cataclysmic LHB would have, in part, resulted in compositionally distinct projectiles, we conclude that the LHB reflects the tail end of accretion. This implies that the giant planet orbital instability occurred during the main phase of planet formation. Last, because of their inner solar system origin, late-accreted bodies cannot be the primary source of Earth's water.

Automated summary

Late accretion refers to the final addition of Earth's mass after the formation of the Moon, including a period of Late Heavy Bombardment (LHB) triggered by a late giant planet orbital instability. Research shows that impactors during the LHB and late accretion were of the same type and originated in the terrestrial planet region, suggesting that the LHB represents the end of accretion. Additionally, late-accreted bodies, originating from the inner solar system, cannot be the primary source of Earth's water.