Pre-Nectarian
| Pre-Nectarian | ||||||
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| Chronology | ||||||
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| Usage information | ||||||
| Celestial body | Earth's Moon | |||||
| Time scale(s) used | Lunar Geologic Timescale | |||||
| Definition | ||||||
| Chronological unit | Period | |||||
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.
Description
[edit]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.
Impact basins
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| For basins with no article, the two prominent craters' names are separately linked to their respective articles. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Names of proposed basins are italicized. |
Relationship to Earth's geologic time scale
[edit]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
[edit]References
[edit]- ^ 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.
- ^ 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
- ^ Don Wilhelms (1987). Geologic History of the Moon. U.S. Geological Survey Professional Paper 1348.
- ^ Wilhelms, Don; McCauley, John; Trask, Newell (1987). The geologic history of the Moon. Professional Paper. US Geological Survey. p. 148. doi:10.3133/pp1348.
- ^ W. Harland; R. Armstrong; A. Cox; L. Craig; A. Smith; D. Smith (1990). A Geologic time scale 1989. Cambridge University Press.
External links
[edit]- Palaeos.org: Hadean eon Archived 2016-07-28 at the Wayback Machine