Mesoarchean

The Mesoarchean (/ˌmiːzoʊɑːrˈkiːən/, also spelled Mesoarchaean) is a geologic era within the Archean Eon, spanning 3,200 to 2,800 million years ago. The era is defined chronometrically and is not referenced to a specific level in a rock section on Earth. Fossils from Australia show that stromatolites have grown on Earth since the Mesoarchean.[1][2] The Pongola glaciation occurred around 2,900 million years ago.[3] The first supercontinent Vaalbara broke up during this era about 2,800 million years ago.

Mesoarchean
3200 – 2800 Ma
Chronology
-4500 —
–
-4000 —
–
-3500 —
–
-3000 —
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-2500 —
–
-2000 —
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-1500 —
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-1000 —
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-500 —
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0 —
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 earliest reefs date from this era, and were probably formed by stromatolites.[1][2] Analysis of oxygen isotopes in cherts led to an oceanic temperature estimate around 55-85 ºC,[4] while other studies of weathering rates postulate average temperatures below 50 ºC.[5] Dinitrogen content in the atmosphere is thought to have been fundamentally similar to today's, and the partial pressure of carbon dioxide was probably lower than 0.7 bar.[6]

See also
  • 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
  1. Allwood, Abigail C.; Walter, Malcolm R.; Kamber, Balz S.; Marshall, Craig P.; Burch, Ian W. (8 June 2006). "Stromatolite reef from the Early Archaean era of Australia". Nature. 441 (7094): 714–718. Bibcode:2006Natur.441..714A. doi:10.1038/nature04764. PMID 16760969.
  2. Nelson, Jon (15 April 1997). "Stromatolites: Our Mysterious Ancient Reefs". Lake Superior Magazine. Archived from the original on 18 February 2019. Retrieved 10 March 2018.
  3. 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. Retrieved 2011-06-19.
  4. Knauth, L. P. Lowe, D. R. High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland group, South Africa, Geol. Soc. Amer. Bull. 115 (2003) 566 – 580.
  5. Sleep, Norman H.; Hessler, Angela M. (January 2006). "Weathering of quartz as an Archean climatic indicator" (PDF). Earth and Planetary Science Letters. 241 (3–4): 594–602. Bibcode:2006E&PSL.241..594S. doi:10.1016/j.epsl.2005.11.020. Archived (PDF) from the original on 10 March 2018. Retrieved 10 March 2018.
  6. Marty, Bernard; Zimmermann, Laurent; Pujol, Magali; Burgess, Ray; Philippot, Pascal (4 October 2013). "Nitrogen Isotopic Composition and Density of the Archean Atmosphere". Science. 342 (6154): 101–104. arXiv:1405.6337. Bibcode:2013Sci...342..101M. doi:10.1126/science.1240971. ISSN 0036-8075. PMID 24051244.
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