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
Lunar geologic timescale -4500 — – -4000 — – -3500 — – -3000 — – -2500 — – -2000 — – -1500 — – -1000 — – -500 — – 0 — Pre-Nectarian Nectarian I m b r i. 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 Orientalis 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.

Millions of years before present

Impact Basins

Impact basins as categorized by Wilhelms et al. (1987)[4] Note: Italicized are proposed basins.

Basin	Diameter (km)	Age Group
Procellarum	3,200	1
South Pole-Aitken	2,500	1
Tsiolkovskiy-Stark	700	2
Grissom-White	600	2
Insularum	600	2
Marginis	580	2
Flamsteed-Billy	570	2
Balmer-Kapteyn	550	2
Werner-Airy	500	2
Pingré-Hausen	300	2
Al-Khwarizmi/King	590	2
Fecunditatis	990	3
Australe	880	3
Tranquillitatis	800	3
Mutus-Vlacq	700	3
Nubium	690	3
Lomonosov-Fleming	620	3
Ingenii	650	4
Poincaré	340	4
Keeler-Heaviside	780	4
Coulomb-Sarton	530	5
Smythii	840	5
Lorentz	360	6
Arnundsen-Ganswindt	355	7
Schiller-Zucchius	325	7
Planck	325	7
Birkhoff	330	7
Freundlich-Sharonov	600	8
Grimaldi	430	9
Apollo	505	9

Relationship to Earth's geologic time scale

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[5] 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.

See also

• Hadean eon-related topics

References

1. Fernandes V. A., Fritz J., Weiss B., Garrick-Bethel and Shuster D. (2013) The bombardment history of the Moon as recorded by 40Ar-39Ar chronology. Meteor. and Planet. Sci. 48, 241–269. DOI: 10.1111/maps.12054.
2. Fritz J., Bitsch B., Kührt E., Morbidelli A., Tornow C., Wünnemann K., Fernandes V.A., Grenfell L.J., Rauer H., Wagner R. and Werner S.C. (2014) Earth-like habitats in planetary systems. Planetary and Space Science 98, 254–267. https://dx.doi.org/ 10.1016/j.pss.2014.03.003i
3. Don Wilhelms (1987). Geologic History of the Moon. U.S. Geological Survey Professional Paper 1348.
4. Wilhelms, Don; McCauley, John; Trask, Newell (1987). "The Geologic History of the Moon": 148. doi:10.3133/pp1348. Cite journal requires |journal= (help)
5. W. Harland; R. Armstrong; A. Cox; L. Craig; A. Smith; D. Smith (1990). A Geologic time scale 1989. Cambridge University Press.

External links

• Palaeos.org: Hadean eon