pre-Nectarian

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 EonFernandes 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.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 (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),{{cite book | title =Geologic History of the Moon | url =http://ser.sese.asu.edu/GHM/ | last = Don Wilhelms | publisher = U.S. Geological Survey Professional Paper 1348 | year = 1987}} but these divisions are not used on any geologic maps. Similarly the later period has also been called the Aitkenian period.

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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{{cite book | title = A Geologic time scale 1989 | publisher = Cambridge University Press | year = 1990 |author1=W. Harland |author2=R. Armstrong |author3=A. Cox |author4=L. Craig |author5=A. Smith |author6=D. Smith }} to subdivide the unofficial terrestrial Hadean eon. In particular, 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.

• {{C|Hadean|Hadean eon–related topics}}

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• [http://www.palaeos.org/Hadean Palaeos.org: Hadean eon] {{Webarchive|url=https://web.archive.org/web/20160728124239/http://www.palaeos.org/Hadean |date=2016-07-28 }}

Category:Hadean