Imbrian

Imbrian
Imbrian
3850 – 3200 Ma PreN I N E C
Chronology
−4500 — – −4000 — – −3500 — – −3000 — – −2500 — – −2000 — – −1500 — – −1000 — – −500 — – 0 —	Pre-Nectarian Nectarian Imbrian Eratosthenian Copernican Late Early
	Periods on the Lunar Geologic Timescale. Axis scale: Millions of years ago.;
Usage information
Celestial body	Earth's Moon
Time scale(s) used	Lunar Geologic Timescale
Definition
Chronological unit	Period

Last updated February 02, 2025

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 end of the Late Heavy Bombardment of the Inner Solar System. The impact that created the huge Mare Imbrium basin occurred at the start of the epoch. The other large basins that dominate the lunar near side (such as Mare Crisium, Mare Tranquillitatis, Mare Serenitatis, and Mare Fecunditatis) were also formed in this period. These basins filled with basalt mostly during the subsequent Late Imbrian epoch. The Early Imbrian was preceded by the Nectarian.

Late Imbrian

In the Lunar geologic timescale, the Late Imbrian epoch occurred between 3,800 million years ago to about 3,200 million years ago. It was the epoch during which the mantle below the lunar basins partially melted and filled them with basalt. The melting is thought to have occurred because the impacts of the Early Imbrian thinned the overlying rock – either causing the mantle to rise because of the reduced pressure on it, bringing molten material closer to the surface, or the top melting as heat flowed upwards through the mantle because of reduced overlying thermal insulation. The majority of lunar samples returned to earth for study come from this epoch.^{[ citation needed ]}

Relationship to Earth's geologic time scale

Since little or no geological evidence on Earth exists from the time spanned by the Early and Late Imbrian epoch of the Moon, the Early and Late Imbrian has been used by at least one notable scientific work^[1] as an unofficial subdivision of the terrestrial Hadean eon.

Related Research Articles

The Hadean is the first and oldest of the four known geologic eons of Earth's history, starting with the planet's formation about 4.6 billion years ago, and ended 4.031 billion years ago. The interplanetary collision that created the Moon occurred early in this eon. The Hadean eon was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary.

<span class="mw-page-title-main">Archean</span> Geologic eon, 4031–2500 million years ago

The Archean Eon, in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history, preceded by the Hadean Eon and followed by the Proterozoic. The Archean represents the time period from 4,031 to 2,500 Mya. The Late Heavy Bombardment is hypothesized to overlap with the beginning of the Archean. The Huronian glaciation occurred at the end of the eon.

Mare Orientale is a lunar mare. It is located on the western border of the near side and far side of the Moon, and is difficult to see from an Earthbound perspective. Images from spacecraft have revealed it to be one of the most striking large scale lunar features, resembling a target ring bullseye.

Mare Cognitum is a lunar mare located in a basin or large crater which sits in the second ring of Oceanus Procellarum. To the northwest of the mare is the Montes Riphaeus mountain range, part of the rim of the buried crater or basin containing the mare. Previously unnamed, the mare received its name in 1964 in reference to its selection as the target for the successful impact probe Ranger 7, the first American spacecraft to return closeup images of the Moon's surface.

Mare Nectaris is a small lunar mare or sea located south of Mare Tranquillitatis southwest of Mare Fecunditatis, on the near side of the Moon. Montes Pyrenaeus borders the mare to the east and Sinus Asperitatis fuses to its northwestern edge. It is 84,000 square kilometers in size.

The lunar geological timescale divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian, Nectarian, and Pre-Nectarian. The boundaries of this time scale are related to large impact events that have modified the lunar surface, changes in crater formation through time, and the size-frequency distribution of craters superposed on geological units. The absolute ages for these periods have been constrained by radiometric dating of samples obtained from the lunar surface. However, there is still much debate concerning the ages of certain key events, because correlating lunar regolith samples with geological units on the Moon is difficult, and most lunar radiometric ages have been highly affected by an intense history of bombardment.

The Copernican Period in the lunar geologic timescale runs from approximately 1.1 billion years ago to the present day. The base of the Copernican period is defined by impact craters that possess bright optically immature ray systems. The crater Copernicus is a prominent example of rayed crater, but it does not mark the base of the Copernican period.

The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, which displays characteristics typical of craters of this age, including a surface that is not significantly eroded by subsequent impacts, but which also does not possess a ray system. The massive basaltic volcanism of the Imbrian period tapered off and ceased during this long span of lunar time. The youngest lunar lava flows identified from orbital images are tentatively placed near the end of this period.

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 form the upper part of the densely cratered terrain found in lunar highlands. The period ended with the formation of the Imbrium basin, which initiated the Imbrian Period. Magnetic anomalies found in some Nectarian Period basins suggest that the Moon possessed a core dynamo magnetic field at that time.

The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.

The Cryptic era is an informal term for the earliest geologic evolution of the Earth and Moon. It is the oldest (informal) era of the Hadean eon, and it is commonly accepted to have begun close to about 4.533 billion years ago when the Earth and Moon formed, and lasted to about 4.15 billion years ago. No samples exist to date the transition between the Cryptic era and the following Basin Groups era for the Moon, though sometimes it is stated that this era ended 4150 million years ago for one or both of these bodies. Neither this time period, nor any other Hadean subdivision, has been officially recognized by the International Commission on Stratigraphy.

The geology of the Moon is quite different from that of Earth. The Moon lacks a true atmosphere, and the absence of free oxygen and water eliminates erosion due to weather. Instead, the surface is eroded much more slowly through the bombardment of the lunar surface by micrometeorites. It does not have any known form of plate tectonics, it has a lower gravity, and because of its small size, it cooled faster. In addition to impacts, the geomorphology of the lunar surface has been shaped by volcanism, which is now thought to have ended less than 50 million years ago. The Moon is a differentiated body, with a crust, mantle, and core.

Basin Groups refers to 9 subdivisions of the lunar Pre-Nectarian geologic period. It is the second era of the Hadean.

The geological history of the Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.

The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere.

The Noachian is a geologic system and early time period on the planet Mars characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water. The absolute age of the Noachian period is uncertain but probably corresponds to the lunar Pre-Nectarian to Early Imbrian periods of 4100 to 3700 million years ago, during the interval known as the Late Heavy Bombardment. Many of the large impact basins on the Moon and Mars formed at this time. The Noachian Period is roughly equivalent to the Earth's Hadean and early Archean eons when Earth's first life forms likely arose.

The Hesperian is a geologic system and time period on the planet Mars characterized by widespread volcanic activity and catastrophic flooding that carved immense outflow channels across the surface. The Hesperian is an intermediate and transitional period of Martian history. During the Hesperian, Mars changed from the wetter and perhaps warmer world of the Noachian to the dry, cold, and dusty planet seen today. The absolute age of the Hesperian Period is uncertain. The beginning of the period followed the end of the Late Heavy Bombardment and probably corresponds to the start of the lunar Late Imbrian period, around 3700 million years ago (Mya). The end of the Hesperian Period is much more uncertain and could range anywhere from 3200 to 2000 Mya, with 3000 Mya being frequently cited. The Hesperian Period is roughly coincident with the Earth's early Archean Eon.

Magma oceans are vast fields of surface magma that exist during periods of a planet's or some natural satellite's accretion when the celestial body is completely or partly molten.

<span class="mw-page-title-main">Volcanism on the Moon</span> Volcanic processes and landforms on the Moon

Volcanism on the Moon is represented by the presence of volcanoes, pyroclastic deposits and vast lava plains on the lunar surface. The volcanoes are typically in the form of small domes and cones that form large volcanic complexes and isolated edifices. Calderas, large-scale collapse features generally formed late in a volcanic eruptive episode, are exceptionally rare on the Moon. Lunar pyroclastic deposits are the result of lava fountain eruptions from volatile-laden basaltic magmas rapidly ascending from deep mantle sources and erupting as a spray of magma, forming tiny glass beads. However, pyroclastic deposits formed by less common non-basaltic explosive eruptions are also thought to exist on the Moon. Lunar lava plains cover large swaths of the Moon's surface and consist mainly of voluminous basaltic flows. They contain a number of volcanic features related to the cooling of lava, including lava tubes, rilles and wrinkle ridges.

References

↑ W. Harland; R. Armstrong; A. Cox; L. Craig; A. Smith; D. Smith (1990). A Geologic time scale 1989. Cambridge University Press.

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[1] W. Harland; R. Armstrong; A. Cox; L. Craig; A. Smith; D. Smith (1990). A Geologic time scale 1989. Cambridge University Press.

[1]

v t e Hadean Eon
Cryptic Basin Groups Nectarian Lower Imbrian
The Hadean does not have any subdivisions recognized by the International Commission on Stratigraphy. These subdivisions represent one proposal that is loosely based on the lunar geologic timescale.