View source for Mesoarchean

{{short description|Third era of the Archean Eon}}
{{Infobox geologic timespan
| name                         = Mesoarchean
| color                        = Mesoarchean
| top_bar                      = all time
| time_start                   = {{period start|mesoarchean}}
| time_end                     = {{period end|mesoarchean}}
<!--Chronology-->  
| timeline                     = Mesoarchean
| proposed_boundaries1         = 3490–2780 Ma
| proposed_boundaries1_ref     = Gradstein et al., 2012
| proposed_subdivision1        = Vaalbaran Period, 3490–3020 Ma
| proposed_subdivision1_coined = Gradstein et al., 2012
| proposed_subdivision2        = Pongolan Period, 3020–2780 Ma
| proposed_subdivision2_coined = Gradstein et al., 2012
<!--Etymology-->
| chrono_name                  =
| strat_name                   =
| name_formality               = Formal
| name_accept_date             =
| alternate_spellings          = Mesoarchaean
| former_names                 =
| proposed_names               =
<!--Usage Information--> 
| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
<!--Definition-->
| chrono_unit                  = Era
| strat_unit                   = Erathem
| proposed_by                  =
| timespan_formality           = Formal
| lower_boundary_def           = Defined Chronometrically
| lower_gssa_accept_date       = {{period start ratification|mesoarchean}}
| upper_boundary_def           = Defined Chronometrically
| upper_gssa_accept_date       = {{period end ratification|mesoarchean}}
|image_map=3000 Ma paleoglobe.png|caption_map=A reconstruction of the Earth's continents during the middle Mesoarchean, c. 3 Ga.{{citation needed|reason=Description on Wikimedia Commons page is "own work" with no cited sources|date=June 2024}}|image_art=Banded iron formation (Goldman Meadows Formation, Mesoarchean; Atlantic City Iron Mine, South Pass, Wyoming, USA) 2 (30749219994).jpg|caption_art=[[Banded iron formation]] created during the Mesoarchean era|image_outcrop=Archean.png|caption_outcrop=Artist impression of the [[Archean]] eon}}

The '''Mesoarchean''' ({{IPAc-en|ˌ|m|iː|z|oʊ|.|ɑr|ˈ|k|iː|ə|n|,_|,|m|E|z|ou|-}} {{respell|MEE|zoh|ar|KEE|ən|,_|MEZ|oh|-}}, also spelled '''Mesoarchaean''') is a [[geology|geologic]] [[era (geology)|era]] in the [[Archean|Archean Eon]], spanning {{Ma|Mesoarchean|Neoarchean}}, which contains the first evidence of modern-style [[Subduction|plate subduction]] and expansion of [[Microorganism|microbial life.]] The era is defined [[Absolute dating|chronometrically]] and is not referenced to a specific level in a rock section on Earth.

== Tectonics ==
The Mesoarchean era is thought to be the birthplace of modern-style plate subduction, based on geologic evidence from the [[Pilbara craton|Pilbara Craton]] in western [[Australia]].<ref>{{cite journal |last1=Mints |first1=M.V. |last2=Belousova |first2=E.A. |last3=Konilov |first3=A.N. |last4=Natapov |first4=L.M. |last5=Shchipansky |first5=A.A. |last6=Griffin |first6=W.L. |last7=O'Reilly |first7=S.Y. |last8=Dokukina |first8=K.A. |last9=Kaulina |first9=T.V. |date=2010 |title=Mesoarchean subduction processes: 2.87 Ga eclogites from the Kola Peninsula, Russia |journal=Geology |issn=0091-7613 |doi=10.1130/G31219.1 |bibcode=2010Geo....38..739M |volume=38 |issue=8 |pages=739–742 }}</ref><ref name=Smithies2007>{{cite journal |last1=Smithies |first1=R. H. |last2=Van Kranendonk |first2=M. J. |last3=Champion |first3=D. C. |date=2007 |title=The Mesoarchean emergence of modern-style subduction |series=Island Arcs: Past and Present |journal=Gondwana Research |issn=1342-937X |doi=10.1016/j.gr.2006.02.001 |bibcode=2007GondR..11...50S |volume=11 |issue=1 |pages=50–68 |url=https://www.sciencedirect.com/science/article/pii/S1342937X06000669|url-access=subscription }}</ref> A [[Convergent boundary|convergent margin]] with a modern-style [[Volcanic arc|oceanic arc]] existed at the boundary between West and East Pilbara approximately 3.12 Ga. By 2.97 Ga, the [[Pilbara|West Pilbara Terrane]] converged with and accreted onto the East Pilbara Terrane.<ref name=Smithies2007/> A [[supercontinent]], [[Vaalbara]], may have existed in the Mesoarchean.<ref>{{cite journal |last1=de Kock |first1=Michiel O. |last2=Evans |first2=David A. D. |last3=Beukes |first3=Nicolas J. |date=2009 |title=Validating the existence of Vaalbara in the Neoarchean|journal=Precambrian Research |issn=0301-9268 |doi=10.1016/j.precamres.2009.07.002 |bibcode=2009PreR..174..145D |volume=174 |issue=1 |pages=145–154 |url=https://www.sciencedirect.com/science/article/pii/S0301926809001429|url-access=subscription }}</ref>

== Environmental conditions ==
Analysis of [[oxygen isotopes]] in Mesoarchean [[Chert|cherts]] has been helpful in reconstructing Mesoarchean surface temperatures.<ref name=Sleep2006>{{cite journal |last1=Sleep |first1=Norman H. |last2=Hessler |first2=Angela M. |date=2006 |title=Weathering of quartz as an Archean climatic indicator |journal=Earth and Planetary Science Letters |bibcode=2006E&PSL.241..594S |doi=10.1016/j.epsl.2005.11.020 |volume=241 |issue=3–4 |pages=594–602 }}</ref> These cherts led researchers to draw an estimate of an oceanic temperature around 55-85°C<ref>{{cite journal |last1=Knauth |first1=L. Paul |last2=Lowe |first2=Donald R. |date=2003 |title=High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland Supergroup, South Africa |journal=Geological Society of America Bulletin |issn=0016-7606 |doi=10.1130/0016-7606(2003)115<0566:HACTIF>2.0.CO;2 |bibcode=2003GSAB..115..566K |volume=115 |pages=566–580 |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/115/5/566/183983/High-Archean-climatic-temperature-inferred-from?redirectedFrom=fulltext|url-access=subscription }}</ref> (131-185 Fahrenheit), while other studies of [[weathering]] rates postulate average temperatures below 50°C (122 Fahrenheit). 

The Mesoarchean atmosphere contained high levels of atmospheric [[methane]] and [[carbon dioxide]], which could be an explanation for the high temperatures during this era.<ref name=Sleep2006/> 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 energy storage|thermal budget]] of ancient Earth.<ref>{{cite journal |last1=Marty |first1=Bernard |last2=Zimmermann |first2=Laurent |last3=Pujol |first3=Magali |last4=Burgess |first4=Ray |last5=Philippot |first5=Pascal |date=2013 |title=Nitrogen isotopic composition and density of the Archean atmosphere |journal=Science |doi=10.1126/science.1240971 |pmid=24051244 |arxiv=1405.6337 |bibcode=2013Sci...342..101M |s2cid=206550098 |volume=342 |issue=6154 |pages=101–104 |url=https://www.science.org/doi/10.1126/science.1240971}}</ref>

{{anchor|Pongola glaciation}}
The [[Pongola glaciation]] occurred around 2.9 Ga, from which there is evidence of ice extending to a palaeolatitude (latitude based on the magnetic field recorded in the rock) of 48 degrees. This glaciation was likely not triggered by the evolution of photosynthetic cyanobacteria, which likely occurred in the interval between the Huronian glaciations and the Makganyene glaciation.<ref>{{cite journal |last1=Kopp |first1=Robert E. |last2=Kirschvink |first2=Joseph L. |last3=Hilburn |first3=Isaac A. |last4=Nash |first4=Cody Z. |date=2005 |title=The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis |journal=Proc. Natl. Acad. Sci. U.S.A. |doi=10.1073/pnas.0504878102 |doi-access=free |bibcode=2005PNAS..10211131K |pmc=1183582 |pmid=16061801 |volume=102 |issue=32 |pages=11131–6}}</ref>

== Early microbial life ==
Microbial life with diverse metabolisms expanded during the Mesoarchean era and produced gases that influenced [[early Earth]]'s [[Atmospheric chemistry|atmospheric composition]]. [[Cyanobacteria]] produced [[Oxygen|oxygen gas]], but oxygen did not begin to accumulate in the atmosphere until later in the [[Archean]].<ref>{{cite journal |last=Lepot |first=Kevin |date=2020 |title=Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon |journal=Earth-Science Reviews |issn=0012-8252 |doi=10.1016/j.earscirev.2020.103296 |doi-access=free |bibcode=2020ESRv..20903296L |s2cid=225413847 |volume=209 |article-number=103296|hdl=20.500.12210/62415 |hdl-access=free }}</ref> Small oases of relatively [[Oxygenation (environmental)|oxygenated]] water did exist in some nearshore shallow marine environments by this era, however.<ref>{{cite journal |last1=Eickmann |first1=Benjamin |last2=Hofmann |first2=Axel |last3=Wille |first3=Martin |last4=Bui |first4=Thi Hao |last5=Wing |first5=Boswell A. |last6=Schoenberg |first6=Ronny |date=15 January 2018 |title=Isotopic evidence for oxygenated Mesoarchaean shallow oceans |journal=[[Nature Geoscience]] |doi=10.1038/s41561-017-0036-x |s2cid=135023426 |volume=11 |issue=2 |pages=133–138 |url=https://www.nature.com/articles/s41561-017-0036-x?error=cookies_not_supported&code=54e99c94-9890-439d-a813-c26d056ce863 |access-date=28 December 2022|url-access=subscription }}</ref>

==See also==
*{{annotated link|Geologic time scale}}
*{{annotated link|Glacial period}}
*{{annotated link|Ice age}}
*{{annotated link|Last glacial period}}

==References==
<references />

==External links==
{{Commons category|Mesoarchean}}
*[https://ghkclass.com/ghkC.html?mesoarchean Mesoarchean (chronostratigraphy scale)]

{{Archean Footer}}
{{Ice Ages}}
{{Geological history|c}}
{{portal bar|Geology|Paleontology}}

[[Category:Archean|*03]]
[[Category:Geological eras]]
[[Category:Precambrian geochronology]]