Pre-Nectarian
Encyclopedia
The Pre-Nectarian Period of the lunar geologic timescale
runs from 4533 million years ago (the time of the initial formation of the Moon
) to 3920 million years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian
period. 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 Late Heavy Bombardment
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), but these divisions are not used on any geologic maps.
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 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.
Lunar geologic timescale
The lunar geological timescale divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian , Nectarian, and Pre-Nectarian...
runs from 4533 million years ago (the time of the initial formation of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
) to 3920 million years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian
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...
period. 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 Late Heavy Bombardment
Late Heavy Bombardment
The Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
that marks the approximate beginning of the Nectarian
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...
Period. The primary Pre-Nectarian lunar highland material is dominated by the rock type anorthosite
Anorthosite
Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar , and a minimal mafic component...
, which suggests that the early stage of lunar crustal formation occurred via mineral crystallization of a global magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
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.
Relationship to Earth's geologic time scale
Since little or no geologicalGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
evidence on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
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
Hadean
The Hadean is the geologic eon before the Archean. It started with the formation of the Earth about 4.7 Ga and ended roughly 3.8 Ga, though the latter date varies according to different sources. The name "Hadean" derives from Hades, Greek for "Underworld", referring to the "hellish"...
eon. In particular, it is sometimes found that the Hadean eon is subdivided into the Cryptic era
Cryptic era
The Cryptic era is an informal term that refers to the earliest geologic evolution of the Earth and Moon. It is the oldest era of the Hadean eon, and it is commonly accepted to have begun close to 4567.17 million years ago when the Earth and Moon formed...
, Basin Groups
Basin Groups
Basin Groups refers to 9 informal subdivisions of the lunar Pre-Nectarian geologic period.-Definition:The motivation for creating the Basin Groups subdivisions was to place 30 pre-Nectarian impact basins into 9 relative age groups...
1-9, Nectarian
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...
and Lower Imbrian
Lower Imbrian
In the lunar geologic timescale, the Early Imbrian epoch occurred between 3850 million years ago to about 3800 million years ago. It overlaps the end of the Late Heavy Bombardment of the inner solar system. The impact which created the huge Mare Imbrium basin occurred at the start of the epoch...
, though the first two of these lunar divisions are informal and collectively make up the Pre-Nectarian.