Basin Groups
Encyclopedia
Basin Groups refers to 9 informal subdivisions of the lunar Pre-Nectarian
geologic period
.
period is defined by the formation of the Nectaris impact basin.
The age of the Nectaris basin is somewhat contentious, with the most frequently cited numbers placing it at 3.92 Ga, or more infrequently at 3.85 Ga. Recently, however, it has been suggested that the Nectaris basin could be, in fact, much older and might have formed at ~4.1 Ga. Basin Groups are not used as a geologic period on any of the United States Geological Survey
lunar geologic maps. Basin Groups 1-9 and the earlier (informal) Cryptic era
together make up the totality of the Pre-Nectarian
period.
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
and Basin Groups 1-9 (which collectively make up the Pre-Nectarian
), and the Nectarian
and Lower Imbrian
. The first lifeforms (self replicating RNA
molecules, see RNA world hypothesis
) may have evolved on earth around 4 bya
during this era.
Pre-Nectarian
The Pre-Nectarian Period of the lunar geologic timescale runs from 4533 million years ago to 3920 million years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period...
geologic period
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...
.
Definition
The motivation for creating the Basin Groups subdivisions was to place 30 pre-Nectarian impact basins into 9 relative age groups. The relative age of the first basin in each group is based on crater densities and superposition relationships, whereas the other basins are included based on weaker grounds. Basin Group 1 has no official age for its base, and the boundary between Basin Group 9 and the NectarianNectarian
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 is defined by the formation of the Nectaris impact basin.
The age of the Nectaris basin is somewhat contentious, with the most frequently cited numbers placing it at 3.92 Ga, or more infrequently at 3.85 Ga. Recently, however, it has been suggested that the Nectaris basin could be, in fact, much older and might have formed at ~4.1 Ga. Basin Groups are not used as a geologic period on any of the United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
lunar geologic maps. Basin Groups 1-9 and the earlier (informal) 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...
together make up the totality of the Pre-Nectarian
Pre-Nectarian
The Pre-Nectarian Period of the lunar geologic timescale runs from 4533 million years ago to 3920 million years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period...
period.
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...
and Basin Groups 1-9 (which collectively make up the Pre-Nectarian
Pre-Nectarian
The Pre-Nectarian Period of the lunar geologic timescale runs from 4533 million years ago to 3920 million years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period...
), and 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...
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...
. The first lifeforms (self replicating RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
molecules, see RNA world hypothesis
RNA world hypothesis
The RNA world hypothesis proposes that life based on ribonucleic acid pre-dates the current world of life based on deoxyribonucleic acid , RNA and proteins. RNA is able both to store genetic information, like DNA, and to catalyze chemical reactions, like an enzyme protein...
) may have evolved on earth around 4 bya
Bya
In astronomy, geology, and paleontology, bya or "b.y.a." is an acronym for billion years ago. This abbreviation is commonly used as a unit of time to denote length of time before the present...
during this era.