First era of the Proterozoic Eon
Paleoproterozoic 2500 – 1600Ma Chronology −2500 —
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Proposed redefinition(s) 2420–1780 Ma Gradstein et al., 2012 Proposed subdivisions Oxygenian Period, 2420–2250 Ma Gradstein et al., 2012 Jatulian/Eukaryian Period, 2250–2060 Ma Gradstein et al., 2012 Columbian Period, 2060–1780 Ma
Gradstein et al., 2012 Etymology Name formality Formal Alternate spelling(s) Palaeoproterozoic 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 GSSA ratified 1990[ 1] Upper boundary definition Defined Chronometrically Upper GSSA ratified 1990[ 1]
ThePaleoproterozoic Era [ 4] Palaeoproterozoic ) is the first of the three sub-divisions (eras ) of theProterozoic eon , and also the longest era of the Earth'sgeological history , spanning from2,500 to 1,600 million years agoGa ). It is further subdivided into fourgeologic periods , namely theSiderian ,Rhyacian ,Orosirian andStatherian .
Paleontological evidence suggests that the Earth's rotational rate ~1.8 billion years ago equated to 20-hour days, implying a total of ~450 days per year.[ 5] continents first stabilized.[clarification needed
TheEarth's atmosphere was originally a weaklyreducing atmosphere consisting largely ofnitrogen ,methane ,ammonia ,carbon dioxide andinert gases , in total comparable toTitan's atmosphere .[ 6] oxygenic photosynthesis evolved incyanobacteria during theMesoarchean , the increasing amount ofbyproduct dioxygen began to deplete thereductants in theocean ,land surface and the atmosphere. Eventually all surface reductants (particularlyferrous iron ,sulfur andatmospheric methane ) were exhausted, and the atmosphericfree oxygen levels soared permanently during the Siderian and Rhyacian periods in anaerochemical event called theGreat Oxidation Event , which brought atmospheric oxygen from near none to up to 10% of the modern level.[ 7]
At the beginning of the precedingArchean eon, almost all existing lifeforms weresingle-cell prokaryotic anaerobic organisms whosemetabolism was based on a form ofcellular respiration that did not require oxygen, andautotrophs were eitherchemosynthetic or relied uponanoxygenic photosynthesis . After the Great Oxygenation Event, the then mainlyarchaea -dominated anaerobicmicrobial mats were devastated as free oxygen is highly reactive and biologically toxic to cellular structures. This was compounded by a 300-million-year -longglobal icehouse event known as theHuronian glaciation — at least partly due to the depletion of atmospheric methane, a powerfulgreenhouse gas — resulted in what is widely considered one of the first and most significantmass extinctions on Earth.[ 8] [ 9] aerobes that evolvedbioactive antioxidants and eventuallyaerobic respiration , and surviving anaerobes were forced to livesymbiotically alongside aerobes in hybrid colonies, which enabled the evolution ofmitochondria ineukaryotic organisms .
The Palaeoproterozoic represents the era from which the oldest cyanobacterial fossils, those ofEoentophysalis belcherensis from the Kasegalik Formation in theBelcher Islands ofNunavut , are known.[ 10] [ 11]
Many crown node eukaryotes (from which the modern-day eukaryotic lineages would have arisen) have been approximately dated to around the time of the Paleoproterozoic Era.[ 12] [ 13] [ 14] [ 15] [ 16] [ 17] [ 18] [ 19] fossils from theChangcheng Group inNorth China provide evidence that eukaryotic life was already diverse by the late Palaeoproterozoic.[ 20]
During this era, the earliest global-scale continent-continent collision belts developed. The associated continent and mountain building events are represented by the 2.1–2.0 Ga Trans-Amazonian andEburnean orogens in South America and West Africa; the ~2.0 GaLimpopo Belt in southern Africa; the 1.9–1.8 GaTrans-Hudson ,Penokean , Taltson–Thelon,Wopmay ,Ungava andTorngat orogens in North America, the 1.9–1.8 GaNagssugtoqidian Orogen in Greenland; the 1.9–1.8 Ga Kola–Karelia,Svecofennian , Volhyn-Central Russian, and Pachelma orogens in Baltica (Eastern Europe); the 1.9–1.8 GaAkitkan Orogen in Siberia; the ~1.95 Ga Khondalite Belt; the ~1.85 Ga Trans-North China Orogen in North China; and the 1.8-1.6 GaYavapai andMazatzal orogenies in southern North America.
That pattern of collision belts supports the formation of a Proterozoic supercontinent namedColumbia orNuna .[ 21] [ 22] [ 23]
Felsic volcanism in what is now northern Sweden led to the formation of theKiruna andArvidsjaur porphyries .[ 24]
Thelithospheric mantle ofPatagonia's oldest blocks formed.[ 25]
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