Mesoarchean

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Mesoarchean
3200 – 2800 Ma
A reconstruction of the Earth's continents during the middle Mesoarchean, c. 3 Ga.
Artist impression of the Archean eon
Banded iron formation created during the Mesoarchean era
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 body
Era
Stratigraphic unitErathem
Time span formalityFormal
Lower boundary definitionDefined Chronometrically
Lower GSSA ratified1991[citation needed]
Upper boundary definitionDefined Chronometrically
Upper GSSA ratified1991[citation needed]

The Mesoarchean (

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

Hypothesized supercontinent Vaalbara during the Mesoarchean era, breaking up in the Neoarchean era
Alternative configuration of Vaalbara

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.[3][4] 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.[4] A supercontinent, Vaalbara, may have existed in the Mesoarchean.[5]

Environmental conditions

Analysis of

oxygen isotopes in Mesoarchean cherts has been helpful in reconstructing Mesoarchean surface temperatures.[6] These cherts led researchers to draw an estimate of an oceanic temperature around 55-85°C[7] while other studies of weathering
rates postulate average temperatures below 50°C.

The Mesoarchean atmosphere contained high levels of 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.[8]

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.[9]

Early microbial life

Microbial life with diverse metabolisms expanded during the Mesoarchean era and produced gases that influenced

oxygenated water did exist in some nearshore shallow marine environments by this era, however.[11]

See also

  • Geologic time scale – System that relates geologic 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
     – Period of major glaciations of the northern hemisphere (115,000–12,000 years ago)

References

External links