Mesoarchean

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Mesoarchean
Chronology
Proposed redefinition(s)3490–2780 Ma
Gradstein et al., 2012
Proposed subdivisionsVaalbaran Period, 3490–3020 Ma

Gradstein et al., 2012
Pongolan Period, 3020–2780 Ma

Gradstein et al., 2012
Etymology
Name formalityFormal
Alternate spelling(s)Mesoarchaean
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitEra
Stratigraphic unitErathem
Time span formalityFormal
Lower boundary definitionDefined Chronometrically
Lower boundary GSSPN/A
GSSP ratifiedN/A
Upper boundary definitionDefined Chronometrically
Upper boundary GSSPN/A
GSSP ratifiedN/A

The Mesoarchean (/ˌmzɑːrˈkən/, also spelled Mesoarchaean) is a geologic era in the Archean Eon, spanning 3,200 to 2,800 million years ago, which contains the first evidence of modern-style plate subduction and expansion of microbial life. The era is defined chronometrically and is not referenced to a specific level in a rock section on Earth.

Tectonics[edit]

The Mesoarchean era is thought to be the birthplace of modern-style plate subduction, based on geologic evidence from the Pilbara craton in western Australia.[1][2] A convergent margin with a modern-style oceanic arc existed at the boundary between West and East Pilbara approximately 3.12 Ga. By 2.97 Ga, the West Pilbara Terrane converged with and accreted onto the East Pilbara Terrane.[2] A supercontinent, Vaalbara, may have existed in the Mesoarchean.[3]

Environmental conditions[edit]

Analysis of oxygen isotopes in Mesoarchean cherts has been helpful in reconstructing Mesoarchean surface temperatures[4]. These cherts led researchers to draw an estimate of an oceanic temperature around 55-85°C[5] while other studies of weathering rates postulate average temperatures below 50°C.

The Mesoarchean atmosphere contained high levels of atmospheric methane and carbon dioxide, which could be an explanation for the high temperatures during this era.[4] Atmospheric dinitrogen content in the Mesoarchean is thought to have been similar to today, suggesting that nitrogen did not play an integral role in the thermal budget of ancient Earth.[6]

The Pongola glaciation occurred around 2.9 Ga.[7]

Early microbial life[edit]

Microbial life with diverse metabolisms expanded during the Mesoarchean era and produced gases that influenced early Earth's atmospheric composition. Cyanobacteria produced oxygen gas, but oxygen did not begin to accumulate in the atmosphere until later in the Archean.[8]

A snapshot of the supercontinent Vaalbara, which has surrounding controversies on its existence and breakup through the Mesoarchean era into the Neoarchean era.

See also[edit]

  • Geologic time scale – System that relates geological strata to time
  • Glacial period – Interval of time within an ice age that is marked by colder temperatures and glacier advances
  • Ice age – Period of long-term reduction in temperature of Earth's surface and atmosphere
  • Last glacial period

References[edit]

  1. ^ Mints, M.V.; Belousova, E.A.; Konilov, A.N.; Natapov, L.M.; Shchipansky, A.A.; Griffin, W.L.; O'Reilly, S.Y.; Dokukina, K.A.; Kaulina, T.V. (2010). "Mesoarchean subduction processes: 2.87 Ga eclogites from the Kola Peninsula, Russia". Geology. 38 (8): 739–742. doi:10.1130/G31219.1. ISSN 0091-7613.
  2. ^ a b Smithies, R. H.; Van Kranendonk, M. J.; Champion, D. C. (2007). "The Mesoarchean emergence of modern-style subduction". Gondwana Research. Island Arcs: Past and Present. 11 (1): 50–68. doi:10.1016/j.gr.2006.02.001. ISSN 1342-937X.
  3. ^ de Kock, Michiel O.; Evans, David A. D.; Beukes, Nicolas J. (2009). "Validating the existence of Vaalbara in the Neoarchean". Precambrian Research. 174 (1): 145–154. doi:10.1016/j.precamres.2009.07.002. ISSN 0301-9268.
  4. ^ a b Sleep, Norman H.; Hessler, Angela M. (2006). "Weathering of quartz as an Archean climatic indicator". Earth and Planetary Science Letters. 241 (3–4): 594–602. Bibcode:2006E&PSL.241..594S. doi:10.1016/j.epsl.2005.11.020.
  5. ^ Knauth, L. Paul; Lowe, Donald R. (2003). "High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland Supergroup, South Africa". Geological Society of America Bulletin. 115: 566–580. ISSN 0016-7606.
  6. ^ Marty, Bernard; Zimmermann, Laurent; Pujol, Magali; Burgess, Ray; Philippot, Pascal (2013). "Nitrogen isotopic composition and density of the Archean atmosphere". Science. 342 (6154): 101–104. doi:10.1126/science.1240971.
  7. ^ Robert E. Kopp; Joseph L. Kirschvink; Isaac A. Hilburn & Cody Z. Nash (2005). "The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis". Proc. Natl. Acad. Sci. U.S.A. 102 (32): 11131–6. Bibcode:2005PNAS..10211131K. PMC 1183582. PMID 16061801.
  8. ^ Lepot, Kevin (2020). "Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon". Earth-Science Reviews. 209: 103296. doi:10.1016/j.earscirev.2020.103296. ISSN 0012-8252.

External links[edit]