Pre-Nectarian

The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.

Pre-Nectarian
4533 – 3920 Ma PreN I N E C
Chronology
−4500 — – −4000 — – −3500 — – −3000 — – −2500 — – −2000 — – −1500 — – −1000 — – −500 — – 0 — Pre-Nectarian Nectarian Imbrian Eratosthenian Copernican Late Early       Periods on the Lunar Geologic Timescale. Axis scale: Millions of years ago.
Usage information
Celestial body	Earth's Moon
Time scale(s) used	Lunar Geologic Timescale
Definition
Chronological unit	Period

Description

Pre-Nectarian rocks are rare in the lunar sample suite; they are mostly composed of lunar highlands material which have been heavily churned, brecciated, and thermally affected by subsequent impacts, particularly during the Heavy Bombardment Eon^[1][2] (HBE; a period of 0.6-1 Gy from the formation of the Moon until at least the formation of the Imbrium Basin ~3.9 Ga, or even later with the formation of Orientale Basin) that marks the approximate beginning of the Nectarian period. The primary pre-Nectarian lunar highland material is dominated by the rock type anorthosite, which suggests that the early stage of lunar crustal formation occurred via mineral crystallization of a global magma ocean.

This geologic period has been informally subdivided into the Cryptic Era (4.533 - 4.172 Ga ago) and Basin Groups 1-9 (4.172 - 3.92 Ga ago),^[3] but these divisions are not used on any geologic maps. Similarly the later period has also been called the Aitkenian period.

Millions of years before present

Impact basins

Lunar impact basins
as categorized by Wilhelms et al. (1987)^[4]

Basin name Diameter Age- group (km) (nr.) Procellarum 3,200 1 South Pole-Aitken 2,500 Tsiolkovskiy-Stark 700 2 Grissom-White 600 Insularum 600 Marginis 580 Flamsteed-Billy 570 Balmer-Kapteyn 550 Werner-Airy 500 Pingré-Hausen 300 Al-Khwarizmi / King 590 Fecunditatis 990 3 Australe 880 Tranquillitatis 800 Mutus-Vlacq 700 Nubium 690 Lomonosov-Fleming 620	Basin name Diameter Age- group (km) (nr.) Ingenii 650 4 Poincaré 340 Keeler-Heaviside 780 Coulomb-Sarton 530 5 Smythii 840 Lorentz 360 6 Amundsen-Ganswindt 355 7 Schiller-Zucchius 325 Planck 325 Birkhoff 330 Freundlich-Sharonov 600 8 Grimaldi 430 9 Apollo 505
	For basins with no article, the two prominent craters' names are separately linked to their respective articles.
	Names of proposed basins are italicized.