Mesoarchean

Mesoarchean
Mesoarchean
3200 – 2800 Ma Pha. Proterozoic Archean Had'n
Chronology
−3200 — – −3150 — – −3100 — – −3050 — – −3000 — – −2950 — – −2900 — – −2850 — – −2800 — –	A ; r ; c ; h ; e ; a ; n Paleoarchean Mesoarchean Neoarchean
	Events of the Mesoarchean. ; Axis scale: millions of years ago.;
Proposed redefinition(s)	3490–2780 Ma; Gradstein et al., 2012;
Proposed subdivisions	Vaalbaran Period, 3490–3020 Ma; Gradstein et al., 2012; Pongolan Period, 3020–2780 Ma; Gradstein et al., 2012;
Etymology
Name formality	Formal
Alternate spelling(s)	Mesoarchaean
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 boundary GSSP	N/A
GSSP ratified	N/A
Upper boundary definition	Defined Chronometrically
Upper boundary GSSP	N/A
GSSP ratified	N/A

Life timeline

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Sexual reproduction

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Earliest multicellular life

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Karoo ice age*

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Earliest apes / humans

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Quaternary ice age*

(million years ago)

*Ice Ages

The Mesoarchean (/ˌmiːzoʊɑːrˈkiːən/, 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[]

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[]

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[]

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.