Basin Groups refers to 9 subdivisions of the lunar
Pre-Nectarian
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 Necta ...
geologic period
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochr ...
. 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 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
Nectarian 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
The United States Geological Survey (USGS), formerly simply known as the 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, ...
lunar geologic maps. Basin Groups 1-9 and the earlier (informal)
Cryptic era together make up the totality of the
Pre-Nectarian
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 Necta ...
period.
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 E ...
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 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 is subdivided into the
Cryptic era and Basin Groups 1-9 (which collectively make up the
Pre-Nectarian
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 Necta ...
), and the
Nectarian 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 ...
. The first lifeforms (self replicating
RNA molecules, see
RNA world hypothesis
The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existenc ...
) may have evolved on earth around 4
bya during this era.
See also
*
*
Cryptic era
*
Geological time scale (Earth)
References
External links
GeoWhen Database
{{Geological history, c
*02
Lunar geologic periods