Pre-Nectarian

The earliest recognized period of lunar geologic history, extending from the Moon’s formation to the beginning of the Nectarian period. Its record is dominated by ancient crust and heavily degraded impact basins.

Lunar geologic timescale: A chronology that divides the Moon’s geologic history into periods and epochs, chiefly using impact basins and crater counts. Pre-Nectarian is the timescale’s earliest recognized period.
Lunar basin: A large impact structure on the Moon, typically formed by an energetic collision that excavated and deformed the crust. Basin formation supplies the major events used to subdivide early lunar history.
Apollo 16: The 1972 Apollo mission that landed in the lunar highlands near the Descartes region and returned rock and soil samples. Its highland samples provide evidence about ancient lunar crust and impact history.
Late Heavy Bombardment: A proposed interval of unusually intense impact bombardment in the inner Solar System, traditionally placed near 3.9 billion years ago. Its timing and intensity remain debated partly because ancient lunar impact records are incomplete.
Nectarian: A lunar geologic period following the Pre-Nectarian, associated with the formation of the Nectaris basin. The formation of this period’s eponymous basin marks the Pre-Nectarian’s end.
South Pole–Aitken basin: The Moon’s largest known impact basin, occupying much of its far-side southern hemisphere. Its ancient age makes it a key candidate marker within early lunar history.
Apollo 17: The final crewed Apollo lunar mission, which landed in the Taurus–Littrow valley in 1972. Its samples include impact-related materials used in reconstructing early lunar chronology.
Lunar cataclysm hypothesis: The hypothesis that a sharp increase in lunar impact rates occurred around 3.9 billion years ago. It interprets some ancient lunar ages differently from a steady decline in impacts.
Lunar impact crater: A roughly circular lunar depression formed when an impactor excavates and alters the surface. Crater abundance and degradation help identify Pre-Nectarian terrain.
Nectaris basin: A large impact basin on the Moon’s near side whose formation defines the beginning of the Nectarian period. Its formation provides the boundary ending the Pre-Nectarian.

Linked from 2 pages