| Neoarchean | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2800 – 2500Ma | |||||||||||||
 A reconstruction of the Earth's continents during the middle Neoarchean, c. 2.65 Ga.[citation needed] | |||||||||||||
| Chronology | |||||||||||||
| |||||||||||||
| Proposed redefinition(s) | 2780–2420 Ma Gradstein et al., 2012 | ||||||||||||
| Proposed subdivisions | Methanian Period, 2780–2630 Ma Gradstein et al., 2012 | ||||||||||||
| Etymology | |||||||||||||
| Name formality | Formal | ||||||||||||
| Alternate spelling(s) | Neoarchaean | ||||||||||||
| Usage information | |||||||||||||
| Celestial body | Earth | ||||||||||||
| Regional usage | Global (ICS) | ||||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||||
| Definition | |||||||||||||
| Chronological unit | Era | ||||||||||||
| Stratigraphic unit | Erathem | ||||||||||||
| Time span formality | Formal | ||||||||||||
| Lower boundary definition | Defined Chronometrically | ||||||||||||
| Lower GSSA ratified | Not formally defined | ||||||||||||
| Upper boundary definition | Defined Chronometrically | ||||||||||||
| Upper GSSA ratified | 1990[1] | ||||||||||||
TheNeoarchean (/ˌniːoʊ.ɑːrˈkiːən/NEE-oh-ar-KEE-ən; also spelledNeoarchaean) is the lastgeologicera in theArchean Eon that spans from 2800 to 2500 million years ago—the period being definedchronometrically and not referencing a specific level in a rock section onEarth. The era is marked by major developments in complex life and continental formation.
This era saw the rise of oxygen in the atmosphere afteroxygenic photosynthesis evolved incyanobacteria as early as theMesoarchean era. The environmental changes that occurred in the Neoarchean such as its developing atmospheric and soil compositions drastically differentiated the era from others in its encouragement ofmicrobial metabolisms to evolve and diversify.[2] The era could have also seen pre-biotic organic molecules being brought to Earth throughmeteorites,comets, or through abiotic reactions. The growth of juvenilecontinental crust as well as the onset ofplate tectonics in the Archean allowed for the colonization of a larger variety of niches bymicroorganisms through increasing the number of rock types present and thereby increasing the surface's chemical diversity.[2] Some noted metabolisms were able to flourish due to changes in the availability of certain metals while others faced famine: an increase incopper present in the environment in the Neoarchean likely favoredaerobic metabolisms.
Oxygenic photosynthesis may have been limited earlier in the Archean era from a lack ofphosphorus stemming from poor biological recycling inanaerobic conditions. This issue was alleviated in the Neoarchean with the abundance of phosphorus inmagmatic rocks, which when combined with other evolvinggeodynamics such as increasing organic matter burial and higher oxidative states in volcanic sulfur and magmatic iron contributed to a large buildup of oxygen in the atmosphere, leading to theGreat Oxidation Event in thePaleoproterozoic era.[2]
The earliest evidence ofmicrobial oxidation of sulphur, dating to approximately 2.52 Ga, comes from the Gamohaan Formation of South Africa, revealing that sulphur-oxidising bacteria had evolved prior to the Great Oxidation Event.[3]
The earliest potential eukaryote fossils come from Neoarchaean deposits in South Africa dating to 2.8 to 2.7 Ga, resembling present day siphonalean microalgae. However, the identity of these microfossils as eukaryotes is highly controversial and remains disputed.[4]
During this era, the supercontinentKenorland is proposed to have formed about 2.7 billion years ago.[5] Kenorland is of particular interest due to it containing deposits ofvolcanic-hosted massive sulphide,gold, anduranium found in theCanadian Shield. With new research, the validity of Kenorland has been questioned in favor of other Neoarchean supercontinent proposals Superia orVaalbara.[5] Improved geologic knowledge suggests that a part of Kenorland, specifically theChurchill Province, was instead a continental development that formed after the Neoarchean era,Nuna, closer to 1.9 billion years ago.[5] This challenge to the reconstruction is based on research studying northern Kenorland's Paleoproterozoic cover as well as the suture between theRae andHearne cratons.
Thesupercontinent cycle can be studied through patterns that describe how Earth's crust and its mineral deposits were preserved over time sincePangaea.[5] Plate tectonics, having developed earlier in the Archean eon,[2] produced the force necessary formetamorphism andmagmatic activity which greatly contributed to these continental changes.[5] Research on how the supercontinents broke apart and combined into different configurations is involved in linking together deep-interior and surface-level processes as well as the assessment of contrasting models of early Paleoproterozoic geodynamic activity.[5]
.jpg)
