The pre-Nectarian period of the
lunar geologic timescale
The lunar geological timescale (or selenological timescale) divides the history of Earth's Moon into five generally recognized periods: the Copernican period, Copernican, Eratosthenian, Imbrian (Late Imbrian, Late and Early Imbrian, Early epochs), ...
runs from 4.533 billion years ago (the time of the initial formation of the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
) to 3.920 billion years ago, when the
Nectaris Basin was formed by a large impact. It is followed by the
Nectarian
The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris for ...
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 (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
The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris for ...
period. The primary pre-Nectarian lunar highland material is dominated by the rock type
anorthosite
Anorthosite () is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most c ...
, which suggests that the early stage of lunar crustal formation occurred via mineral crystallization of a global
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
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.
Impact basins
Relationship to Earth's geologic time scale
Since little or no
geological
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...
evidence on
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
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
The Hadean ( ) is a Eon (geology), geologic eon of History of Earth, Earth history preceding the Archean. On Earth, the Hadean began with the Formation of the Earth, planet's formation about 4.54 billion years ago (although the start of the H ...
eon
Eon or Eons may refer to: Time
* Aeon, an indefinite long period of time
* Eon (geology), a division of the geologic time scale
Arts and entertainment
Fictional characters
* Eon, in the 2007 film ''Ben 10: Race Against Time''
* Eon, in the ...
. In particular, it is sometimes found that the
Hadean eon
The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid material ...
is subdivided into the
Cryptic era
Cryptic may refer to:
In science:
* Cryptic species complex, a group of species that are very difficult to distinguish from one another
* Crypsis, the ability of animals to blend in to avoid observation
* Cryptic era, earliest period of the Eart ...
,
Basin Groups
Basin Groups refers to 9 subdivisions of the lunar Pre-Nectarian geologic period. It is the second era of the Hadean.
Definition
The motivation for creating the Basin Groups subdivisions was to place 30 pre-Nectarian impact basins into 9 relativ ...
1-9,
Nectarian
The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris for ...
and
Lower Imbrian
The Imbrian is a lunar geologic period divided into two epochs, the Early and Late.
Early Imbrian
In the lunar geologic timescale, the Early Imbrian epoch occurred from 3,850 million years ago to about 3,800 million years ago. It overlaps the en ...
, though the first two of these lunar divisions are informal and collectively make up the pre-Nectarian.
See also
*
References
External links
Palaeos.org: Hadean eon{{Webarchive, url=https://web.archive.org/web/20160728124239/http://www.palaeos.org/Hadean , date=2016-07-28
Hadean