Ай геологиясы: Нектарийге дейінгі кезең

Geologic period, 4533 to 3920 million years ago
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 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 (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), but these divisions are not used on any geologic maps. Similarly the later period has also been called the Aitkenian period.

+ Lunar impact basinsas categorized by Wilhelms et al. (1987) 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 Arnundsen Ganswindt 355 7 Schiller Zucchius 325 Planck 325 Birkhoff 330 Freundlich Sharonov 600 8 Grimaldi 430 9 Apollo 505

Since little or no geological evidence on Earth exists from the time spanned by the pre Nectarian period of the Moon, the pre Nectarian has been used as a guide by at least one notable scientific work to subdivide the unofficial terrestrial Hadean eon. In particular, it is sometimes found that the Hadean eon is subdivided into the Cryptic era, Basin Groups 1 9, Nectarian and Lower Imbrian, though the first two of these lunar divisions are informal and collectively make up the pre Nectarian.