Lunar geologic timescale

Lunar geologic timescale
Name	Lunar geologic timescale
Time start	4567 Ma
Time end	0 Ma
Era	Hadean–Quaternary (analogous)
Introduced	1960s

Lunar geologic timescale The lunar geologic timescale organizes the stratigraphy and chronology of the Moon using mapped lithologies, crater density, sample ages, and remote sensing, providing a framework comparable to the Geologic time scale used on Earth. It is applied in studies by institutions such as the United States Geological Survey, NASA, European Space Agency, and the Soviet Union era Luna programme teams, and is informed by returned samples from missions like Apollo program and Luna. The timescale underpins correlations between lunar events, solar system bombardment histories, and planetary geology analyses by groups including the International Astronomical Union.

Overview and Definitions

The timescale divides lunar history into formal and informal intervals defined by stratigraphic markers identified in maps produced by the United States Geological Survey, stratigraphers at the Smithsonian Institution, and researchers from institutions such as the Jet Propulsion Laboratory and Moscow State University. Key terms include chronostratigraphy, used by bodies like the International Commission on Stratigraphy for terrestrial work, and relative stratigraphy applied in lunar mapping by teams from the Lunar and Planetary Institute and the Planetary Science Institute. Definitions rely on boundaries tied to events recognized by investigators from Caltech, Massachusetts Institute of Technology, and Brown University.

Chronostratigraphic Divisions

Standard divisions include the Pre-Nectarian, Nectarian, Imbrian, Eratosthenian, and Copernican systems, terms established through collaborative work involving experts from Harvard University, University of Arizona, and the Max Planck Institute for Solar System Research. The Imbrian is often split into Early and Late Imbrian in publications by California Institute of Technology teams analyzing Apollo samples. Each division is tied to mapped basins studied by investigators at University College London and Brown University and to crater-forming events cataloged in compilations by researchers at the Lunar and Planetary Laboratory.

Basis and Methods of Dating

Dating methods combine radiometric age determinations from samples returned by the Apollo program and Luna missions, crater counting calibrated using chronologies developed at Caltech and the Southwest Research Institute, and stratigraphic superposition mapped by the United States Geological Survey and the Lunar and Planetary Institute. Isotopic systems employed include uranium–lead analyses by teams at Carnegie Institution for Science, argon–argon methods refined at University of Oxford, and samarium–neodymium work from laboratories at Johnson Space Center. Remote sensing datasets from Clementine, Lunar Reconnaissance Orbiter, and Kaguya (SELENE) missions provide spectral and morphology constraints used by researchers at NASA and Japan Aerospace Exploration Agency.

Correlation with Terrestrial and Solar System Events

Researchers at Brown University, Harvard University, and the Smithsonian Institution correlate lunar stratigraphy with the late heavy bombardment hypothesis proposed in contexts involving Carl Sagan and debated in studies by teams at Southwest Research Institute and University of Colorado Boulder. Correlations extend to the formation age of the Earth–Moon system explored by investigators from Caltech and MIT, and to meteorite chronologies studied at the Natural History Museum, London and the Field Museum. Lunar basin-forming events are compared with impact histories on Mercury, Mars, and asteroid populations like the Main Belt as analyzed by researchers at the Max Planck Institute for Solar System Research and the INAF.

Geological Processes and Major Events by Period

The Pre-Nectarian encompasses accretion and early differentiation tied to work by scientists at Carnegie Institution for Science and studies of the Moon's crustal formation by University of Arizona labs. The Nectarian records basin formation as characterized in mapping by the United States Geological Survey and basin analyses by Brown University. The Imbrian includes mare basalt volcanism interpreted from Apollo basalt suites handled at Johnson Space Center and effusive histories modeled by teams at Caltech. The Eratosthenian reflects decreasing volcanic activity recognized in publications from Lunar and Planetary Institute researchers, while the Copernican is marked by young, bright-ray craters cataloged using data from Lunar Reconnaissance Orbiter and curated by the Smithsonian Institution.

Stratigraphic Units and Key Formations

Major stratigraphic units include the highland anorthosite crust sampled by Apollo 16 teams and analyzed by geochemists at Carnegie Institution for Science, the basaltic mare units investigated by Apollo 11 and Apollo 12 teams and studied at Johnson Space Center, and basin ejecta sequences such as those from the Imbrium Basin mapped by scientists at the United States Geological Survey and Harvard University. Key formations recognized in global maps are named following conventions promoted by the International Astronomical Union and formalized in atlases published by NASA and the United States Geological Survey.

History of Classification and Revisions

Origins of the lunar timescale trace to mid-20th century mapping efforts by the United States Geological Survey and the Soviet Luna programme teams, formalization during the Apollo program era with contributions from Caltech, Harvard University, and NASA scientists, and subsequent refinements using radiometric ages from Johnson Space Center laboratories and crater-count calibration updates from researchers at Southwest Research Institute and Brown University. Later epochs of revision involve datasets from Clementine, Lunar Reconnaissance Orbiter, and international teams at the European Space Agency and Japan Aerospace Exploration Agency integrating remote sensing, sample analysis, and stratigraphic nomenclature.

Category:Lunar geology