Along the Acasta River, Northwest Territories, Canada 65°10′26″N115°33′14″W / 65.1738°N 115.5538°W / 65.1738; -115.5538
Lower GSSA ratified
2023[1]
Upper boundary definition
Defined Chronometrically
Upper GSSA ratified
1991[2]
The Archean Eon (IPA: /ɑːrˈkiːən/ar-KEE-ən, also spelled Archaean or Archæan), 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 Ma (millions of years ago). The Late Heavy Bombardment is hypothesized to overlap with the beginning of the Archean. The Huronian glaciation occurred at the end of the eon.
The Earth during the Archean was mostly a water world: there was continental crust, but much of it was under an ocean deeper than today's oceans. Except for some rare relict crystals, today's oldest continental crust dates back to the Archean. Much of the geological detail of the Archean has been destroyed by subsequent activity. The Earth's atmosphere was also vastly different in composition from today's: the prebiotic atmosphere was a reducing atmosphere rich in methane and lacking free oxygen.
The earliest known life, mostly represented by shallow-water microbial mats called stromatolites, started in the Archean and remained simple prokaryotes (archaea and bacteria) throughout the eon. The earliest photosynthetic processes, especially those by early cyanobacteria, appeared in the mid/late Archean and led to a permanent chemical change in the ocean and the atmosphere after the Archean.
^"Global Boundary Stratotype Section and Point". International Commission of Stratigraphy. Retrieved 29 October 2023.
^Plumb, K. A. (1 June 1991). "New Precambrian time scale". Episodes. 14 (2): 139–140. doi:10.18814/epiiugs/1991/v14i2/005.
The Archean Eon (IPA: /ɑːrˈkiːən/ ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the...
ago and was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary. Hadean rocks are...
an informal unit of geologic time, subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of...
Archean subduction is a contentious topic involving the possible existence and nature of subduction in the Archean, a geologic eon extending from 4.0-2...
longest eon of the Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozoic, and is the most recent part of the Precambrian...
Archean felsic volcanic rocks are felsic volcanic rocks that were formed in the Archean Eon (4 to 2.5 billion years ago). The term "felsic" means that...
Archean Soundtrack are a British rock/hip hop band from London, England. It was formed by actors from the accredited East 15 Acting School in 2009. Archean...
ɑːrˈkiːən/ EE-oh-ar-KEE-ən; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record. It spans 431 million years, from the end of...
these mountains to rolling hills. The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the...
events took place in the early to middle Archean. Significant cratonization continued into the late Archean, accompanied by voluminous mafic magmatism...
formation of the planet and ended 4.0 billion years ago. The following Archean and Proterozoic eons produced the beginnings of life on Earth and its earliest...
The Dharwar Craton is an Archean continental crust craton formed between 3.6-2.5 billion years ago (Ga), which is located in southern India and considered...
MEE-zoh-ar-KEE-ən, MEZ-oh-, also spelled Mesoarchaean) is a geologic era in the Archean Eon, spanning 3,200 to 2,800 million years ago, which contains the first...
"Australian island arcs through time: Geodynamic implications for the Archean and Proterozoic". Gondwana Research. 19 (3): 716–734. Bibcode:2011GondR...
continents. The rock exposed in the oldest regions of shields, which is of Archean age (over 2500 million years old), mostly belong to granite-greenstone...
that formed at different times in Earth's history: Archean and Phanerozoic subcontinental mantle. Archean lithosphere is strongly depleted in fertile melt...
NEE-oh-ar-KEE-ən; also spelled Neoarchaean) is the last geologic era in the Archean Eon that spans from 2800 to 2500 million years ago—the period being defined...
arc largely consists of Archean age rocks of the Superior craton. In areal distribution, these rocks consist of about 60% Archean granitic plutons and granitic...
February 2024. eukar Brocks JJ, Logan GA, Buick R, Summons RE (August 1999). "Archean molecular fossils and the early rise of eukaryotes". Science. 285 (5430):...
spelled Palaeoarchaean (formerly known as the early Archean), is a geologic era within the Archean Eon. The name derives from Greek "Palaios" ancient....
Stromatolites were much more abundant in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria, younger (that...
East Antarctica is geologically varied. Its formation began during the Archean Eon (4,000 Ma–2,500 Ma), and stopped during the Cambrian Period. It is...
Vaalbara today Vaalbara is a hypothetical Archean supercontinent consisting of the Kaapvaal Craton (now in eastern South Africa) and the Pilbara Craton...
Cenozoic, although fossilized soils are preserved from as far back as the Archean. Collectively the Earth's body of soil is called the pedosphere. The pedosphere...
climate of the Archean is not well known, the study of the oxygen isotopes in the cherts of the time seem to show that the climate of the Archean was warm or...
chronostratigraphic eonothem. There are four formally defined eons: the Hadean, Archean, Proterozoic and Phanerozoic. An era is the second largest geochronologic...
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