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 and geochronology. It is used primarily by Earth scientists to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardised international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units.
The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.
The Hadean is the first and oldest of the four known geologic eons of Earth's history, starting with the planet's formation about 4.54 Bya, now defined as Mya set by the age of the oldest solid material in the Solar System found in some meteorites about 4.567 billion years old. The supposed interplanetary collision that created the Moon occurred early in this eon. The Hadean ended 4.031 billion years ago and was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary.
Mare Fecunditatis is a lunar mare in the eastern half of the visible Moon. The mare has a maximum diameter of 840 km.
Mare Humboldtianum is a lunar mare located just to the east of Mare Frigoris, in the center of Humboldtianum basin. It is located along the northeastern limb of the Moon, and continues on to the far side. Due to its location, the visibility of this feature can be affected by libration, and on occasion it can be hidden from view from Earth.
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 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. Ejecta from Nectaris form the upper part of the densely cratered terrain found in lunar highlands.
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 Vredefort impact structure is one of the largest verified impact structures on Earth. The crater, which has since been eroded away, has been estimated at 170–300 kilometres (110–190 mi) across when it was formed. The remaining structure, comprising the deformed underlying bedrock, is located in present-day Free State province of South Africa. It is named after the town of Vredefort, which is near its centre. The structure's central uplift is known as the Vredefort Dome. The impact structure was formed during the Paleoproterozoic Era, 2,023 billion years ago. It is the second-oldest known impact structure on Earth, after Yarrabubba.
The Eoarchean is the first era of the Archean Eon of the geologic record. It spans 431 million years, from the end of the Hadean Eon 4031 Mya to the start of the Paleoarchean Era 3600 Mya. The beginnings of life on Earth have been dated to this era and evidence of archaea and cyanobacteria date to 3500 Mya, comparatively shortly after the Eoarchean. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar.
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 history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution.
The oldest dated rocks formed on Earth, as an aggregate of minerals that have not been subsequently broken down by erosion or melted, are more than 4 billion years old, formed during the Hadean Eon of Earth's geological history. Meteorites that were formed in other planetary systems can pre-date Earth. Particles from the Murchison meteorite were dated in January 2020 to be 7 billion years old.
The Borealis quadrangle is a quadrangle on Mercury surrounding the north pole down to 65° latitude. It was mapped in its entirety by the MESSENGER spacecraft, which orbited the planet from 2008 to 2015, excluding areas of permanent shadow near the north pole. Only approximately 25% of the quadrangle was imaged by the Mariner 10 spacecraft during its flybys in 1974 and 1975. The quadrangle is now called H-1.
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized astronomical event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided into the terrestrial planets and their natural satellites of the inner Solar System, including Mercury, Venus, Earth and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although it used to be widely accepted, it remained difficult to provide an overwhelming amount of evidence for the hypothesis. However, recent re-appraisal of the cosmo-chemical constraints indicates that there was likely no late spike in the bombardment rate.
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 the first life forms likely arose.
Pre-Tolstojan, also Pretolstojan Period, refers to the oldest period of the history of Mercury, 4500–3900 MYA. It is the "first period of the Eomercurian Era and of the Mercurian Eon, as well as being the first period in Mercury's geologic history", and refers to its formation and the 600 million or so years in its aftermath. Mercury was formed with a tiny crust, mantle, and a giant core and as it evolved it faced heavy bombardments that created most of the craters and intercrater plains seen on the planet's surface today. Many of the smaller basins and multi-ring basins were created during this period. Considered a "dead" planet, its geology is highly diverse with craters forming the dominant terrain.
The Chaotian is a proposed time division of the geologic time scale. First proposed in 2010 as an eon, it is named after Chaos, the primeval void in Greek mythology. This proposal defines the Chaotian eon as a Solar System-wide time between the initiation of planetary formation and the hypothesised collision of the trojan dwarf planet Theia with the proto-Earth.
The Imbrian is a lunar geologic period divided into two epochs, the Early and Late.
