Mesoarchean
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The Mesoarchean (, also spelled Mesoarchaean) is a
geologic Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ...
era in the
Archean Eon The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Archea ...
, spanning , 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 The Pilbara () is a large, dry, thinly populated region in the north of Western Australia. It is known for its Aboriginal peoples; its ancient landscapes; the red earth; and its vast mineral deposits, in particular iron ore. It is also a g ...
craton in western
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
. 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. A
supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...
,
Vaalbara Vaalbara was an Archean supercontinent consisting of the Kaapvaal Craton (now in eastern South Africa) and the Pilbara Craton (now in north-western Western Australia). E. S. Cheney derived the name from the last four letters of each craton's name ...
, may have existed in the Mesoarchean.


Environmental conditions

Analysis of oxygen isotopes in Mesoarchean cherts has been helpful in reconstructing Mesoarchean surface temperatures. These cherts led researchers to draw an estimate of an oceanic temperature around 55-85°C while other studies of
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
rates postulate average temperatures below 50°C. The Mesoarchean atmosphere contained high levels of atmospheric
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
and
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, which could be an explanation for the high temperatures during this era. 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. The Pongola
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate bet ...
occurred around 2.9 Ga, triggered by the evolution of atmospheric photosynthesis.


Early microbial life

Microbial life with diverse metabolisms expanded during the Mesoarchean era and produced gases that influenced
early Earth The early Earth is loosely defined as Earth in its first one billion years, or gigayear (Ga, 109y). The “early Earth” encompasses approximately the first gigayear in the evolution of our planet, from its initial formation in the young Solar ...
's atmospheric composition.
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
produced
oxygen gas Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
, but oxygen did not begin to accumulate in the atmosphere until later in the
Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...
.


See also

* * * *


References


External links


Mesoarchean (chronostratigraphy scale)
*03 Geological eras Precambrian geochronology {{Geochronology-stub