Contents

Paleoproterozoic

First era of the Proterozoic Eon

Paleoproterozoic
2500 – 1600 Ma Pha. Proterozoic Archean Had.
Paleoproterozoic stromatolites
Chronology
−2500 — – −2400 — – −2300 — – −2200 — – −2100 — – −2000 — – −1900 — – −1800 — – −1700 — – −1600 — – P r o t e r o z o i c A Neoarchean P a l a e o p r o t e r o z o i c Mesoproterozoic Siderian Rhyacian Orosirian Statherian   An approximate timescale of key Paleoproterozoic events. Axis scale: millions of years ago.
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	1991[1]
Upper boundary definition	Defined Chronometrically
Upper GSSA ratified	1991[1]

The Paleoproterozoic Era^[4] (also spelled Palaeoproterozoic) is the first of the three sub-divisions (eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from 2,500 to 1,600 million years ago (2.5–1.6 Ga). It is further subdivided into four geologic periods, namely the Siderian, Rhyacian, Orosirian and Statherian.

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] It was during this era that the continents first stabilized.^{[clarification needed]}

Atmosphere[edit]

The Earth's atmosphere was originally a weakly reducing atmosphere consisting largely of nitrogen, methane, ammonia, carbon dioxide and inert gases, in total comparable to Titan's atmosphere.^[6] When oxygenic photosynthesis evolved in cyanobacteria during the Mesoarchean, the increasing amount of byproduct dioxygen began to deplete the reductants in the ocean, land surface and the atmosphere. Eventually all surface reductants (particularly ferrous iron, sulfur and atmospheric methane) were exhausted, and the atmospheric free oxygen levels soared permanently during the Siderian and Rhyacian periods in an aerochemical event called the Great Oxidation Event, which brought atmospheric oxygen from near none to up to 10% of the modern level.^[7]

Life[edit]

At the beginning of the preceding Archean eon, almost all existing lifeforms were single-cell prokaryotic anaerobic organisms whose metabolism was based on a form of cellular respiration that did not require oxygen, and autotrophs were either chemosynthetic or relied upon anoxygenic photosynthesis. After the Great Oxygenation Event, the then mainly archaea-dominated anaerobic microbial mats were devastated as free oxygen is highly reactive and biologically toxic to cellular structures. This was compounded by a 300-million-year-long global icehouse event known as the Huronian glaciation — at least partly due to the depletion of atmospheric methane, a powerful greenhouse gas — resulted in what is widely considered one of the first and most significant mass extinctions on Earth.^[8][9] The organisms that thrived after the extinction were mainly aerobes that evolved bioactive antioxidants and eventually aerobic respiration, and surviving anaerobes were forced to live symbiotically alongside aerobes in hybrid colonies, which enabled the evolution of mitochondriaineukaryotic organisms.

The Palaeoproterozoic represents the era from which the oldest cyanobacterial fossils, those of Eoentophysalis belcherensis from the Kasegalik Formation in the Belcher IslandsofNunavut, are known.^[10]

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.^[11][12][13] While there is some debate as to the exact time at which eukaryotes evolved,^[14][15] current understanding places it somewhere in this era.^[16][17][18] Statherian fossils from the Changcheng GroupinNorth China provide evidence that eukaryotic life was already diverse by the late Palaeoproterozoic.^[19]

Geological events[edit]

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 and Eburnean 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 and Torngat 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 and Mazatzal orogenies in southern North America.

That pattern of collision belts supports the formation of a Proterozoic supercontinent named ColumbiaorNuna.^[20][21] That continental collisions suddenly led to mountain building at large scale is interpreted as having resulted from increased biomass and carbon burial during and after the Great Oxidation Event: Subducted carbonaceous sediments are hypothesized to have lubricated compressive deformation and led to crustal thickening.^[22]

Felsic volcanism in what is now northern Sweden led to the formation of the Kiruna and Arvidsjaur porphyries.^[23]

The lithospheric mantleofPatagonia's oldest blocks formed.^[24]

Wikimedia Commons has media related to Paleoproterozoic.

See also[edit]

• Boring Billion – Earth history, 1.8 to 0.8 billion years ago
• Suavjärvi impact structure – Lake and claimed impact structure in Karelia, northwest Russia
• Francevillian biota – Possible Palaeoproterozoic multicellular fossils from Gabon
• Vredefort impact structure – Largest verified impact structure on Earth, about 2 billion years old
• Sudbury Basin – Third largest verified astrobleme on earth, remains of an Paleoproterozoic Era impact
• Neoarchean – Fourth era of the Archean Eon, which immediately preceded the Paleoproterozoic

References[edit]

External links[edit]

• EssayWeb Paleoproterozoic Era
• First breath: Earth's billion-year struggle for oxygen New Scientist, #2746, 5 February 2010 by Nick Lane. Posits an earlier much longer snowball period, c2.4 - c2.0 Gya, triggered by the Great Oxygenation Event.
• The information on eukaryotic lineage diversification was gathered from a New York Times opinion blog by Olivia Judson. See the text here: [1].
• Paleoproterozoic (chronostratigraphy scale)