The Paleoproterozoic Era (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 (2.5–1.6 Year). It is further subdivided into four , 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.
Atmosphere
The Earth's atmosphere was originally a weakly reducing atmosphere consisting largely of
nitrogen,
methane,
ammonia,
carbon dioxide and
, in total comparable to Titan's atmosphere.
When oxygenic photosynthesis evolved in
cyanobacteria during the
Mesoarchean, the increasing amount of
byproduct dioxygen began to deplete the
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.
Life
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
were either
chemosynthetic or relied upon anoxygenic photosynthesis. After the Great Oxygenation Event, the then mainly
archaea-dominated anaerobic
were devastated as free oxygen is highly reactive and biologically toxic to cellular structures. This was compounded by a 300-
million years-long
icehouse Earth 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
on Earth.
The organisms that thrived after the extinction were mainly
that evolved bioactive antioxidants and eventually aerobic respiration, and surviving anaerobes were forced to live
alongside aerobes in hybrid colonies, which enabled the evolution of
mitochondria in eukaryotic organisms.
The Palaeoproterozoic represents the era from which the oldest cyanobacterial fossils, those of Eoentophysalis belcherensis from the Kasegalik Formation in the Belcher Islands of Nunavut, are known.
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.
Geological events
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 orogeny Orogeny in South America and West Africa; the ~2.0 Ga
Limpopo Belt in southern Africa; the 1.9–1.8 Ga Trans-Hudson,
Penokean orogeny, Taltson–Thelon,
Wopmay orogen, Ungava and Torngat orogens in North America, the 1.9–1.8 Ga Nagssugtoqidian 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 Ga
Akitkan 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 Ga
Yavapai orogeny and
Mazatzal orogeny orogenies in southern North America.
That pattern of collision belts supports the formation of a Proterozoic supercontinent named Columbia or Nuna.[John Parnell, Connor Brolly: Increased biomass and carbon burial 2 billion years ago triggered mountain building. Nature Communications Earth & Environment, 2021, (Open Access).]
Felsic volcanism in what is now northern Sweden led to the formation of the Kiruna Porphyry and Arvidsjaur porphyries.
The lithospheric mantle of Patagonia's oldest blocks formed.
See also
-
, which immediately preceded the Paleoproterozoic
External links
