Mesoarchean
Template:Short description Template:Infobox geologic timespan
The Mesoarchean (Template:IPAc-en Template:Respell, also spelled Mesoarchaean) is a geologic era in the Archean Eon, spanning Template:Ma, 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
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.<ref>Template:Cite journal</ref><ref name=Smithies2007>Template:Cite journal</ref> 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.<ref name=Smithies2007/> A supercontinent, Vaalbara, may have existed in the Mesoarchean.<ref>Template:Cite journal</ref>
Environmental conditions
Analysis of oxygen isotopes in Mesoarchean cherts has been helpful in reconstructing Mesoarchean surface temperatures.<ref name=Sleep2006>Template:Cite journal</ref> These cherts led researchers to draw an estimate of an oceanic temperature around 55-85°C<ref>Template:Cite journal</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 budget of ancient Earth.<ref>Template:Cite journal</ref>
Template:Anchor 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>Template:Cite journal</ref>
Early microbial life
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.<ref>Template:Cite journal</ref> Small oases of relatively oxygenated water did exist in some nearshore shallow marine environments by this era, however.<ref>Template:Cite journal</ref>
See also
References
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External links
Template:Archean Footer Template:Ice Ages Template:Geological history Template:Portal bar