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, Eratosthenian, Imbrian ( Late and Early epochs), Nectarian, and Pre-Nectarian. The boundar ...
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 Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
) to 3.920 billion years ago, when the
Nectaris Basin
Mare Nectaris (Latin ''nectaris'', the "Sea of Nectar") is a small lunar mare or sea (a volcanic lava plain noticeably darker than the rest of the Moon's surface) located south of Mare Tranquillitatis southwest of Mare Fecunditatis, on the near ...
was formed by a large impact. It is followed by the
Nectarian
The Nectarian Period of the lunar geologic timescale was from 3.920 billion years ago to 3.850 billion 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 Orientale Basin) that marks the approximate beginning of the
Nectarian
The Nectarian Period of the lunar geologic timescale was from 3.920 billion years ago to 3.850 billion 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 rock, 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 ...
, 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 (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
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 the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...
evidence on
Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
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 the first and oldest of the four geologic eons of Earth's history, starting with the planet's formation about 4.6 billion years ago (estimated 4567.30 ± 0.16 million years ago set by the age of the oldest solid material ...
eon. In particular, the
Hadean eon
The Hadean ( ) is the first and oldest of the four geologic eons of Earth's history, starting with the planet's formation about 4.6 billion years ago (estimated 4567.30 ± 0.16 million years ago set by the age of the oldest solid material ...
is subdivided into the
Cryptic era,
Basin Groups 1-9,
Nectarian
The Nectarian Period of the lunar geologic timescale was from 3.920 billion years ago to 3.850 billion 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, 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