Huronian glaciation

The Huronian glaciation (or Makganyene glaciation)[1] was a period where several ice ages occurred during the deposition of the Huronian Supergroup. The deposition of the Huronian extended from 2.5 billion years ago (Gya) to 2.2 Gya, during the Siderian and Rhyacian periods of the Paleoproterozoic era. This led to the deposition of several diamictites. They are, from the oldest to youngest, the Ramsay, Bruce, and Gowganda Formations. This was not a time of continuous glaciation. Most of the deposits of the Huronian are typical passive margin deposits in a marine setting. Although the glaciations were expected to be extensive, there's no solid evidence as of yet, that it was a snowball Earth scenario. The diamictites within the Huronian are on par in thickness with Quaternary analogs. The term Huronian is a lithostratigraphic supergroup and should not be used to describe glacial cycles. The North American Stratigraphic Code, defines the proper naming of geologic physical and chrono units.[2] Diachronic or geochronometric units should be used. Evidence for this early ice age comes from glacial deposits identified within stratigraphic record the Huronian Supergroup. Within it are three distinct formations of diamictite. Although there are other glacial deposits recognized throughout the world, the Huronian is restricted to the North American Midwest. Other deposits are known from South Africa.[3] The Huronian glaciation broadly coincides with the Great Oxygenation Event (GOE), a time when increased atmospheric oxygen decreased atmospheric methane. The oxygen combined with the methane to form carbon dioxide and water, reducing the efficacy of the greenhouse effect as water precipitated out of the air.[4] The combination of increasing free oxygen and climatic stresses likely caused an extinction event, the first and longest lasting in the Earth's history.[5][6]

Discovery and name

In 1907, Arthur Philemon Coleman first inferred a "lower Huronian ice age"[7][8] from analysis of a geological formation near Lake Huron in North America. This formation consists of two non-glacial sediment deposits found between three horizons of glacial deposits of the Huronian Supergroup, deposited between 2.5 and 2.2 Gya.[9] Despite the name, the Huronian glaciation does not in fact represent a single glaciation. The confusion of the terms glaciation and ice age has led to the more recent impression that the entire time period represents a single glacial event, with some proposing that the Earth was entirely frozen.[10] However, only a small minority of the identified rock formations are known to be associated with glacial conditions, and evidence for a global glaciation is lacking in the rock record.

Other evidence

The Gowganda Formation (2.3 Gya) contains "the most widespread and most convincing glaciogenic deposits of this era", according to Eyles and Young. Similar deposits are found in Michigan (2.23–2.15 Gya), the Black Hills (2.6–1.6 Gya), Chibougamau, Canadian Northern Territories (2.1 Gya) and Wyoming. Similar age deposits occur in the Griquatown Basin (2.3 Gya), India (1.8 Gya) and Australia (2.5—2.0 Gya).[9]

Geological context

The tectonic setting was one of a rifting continental margin. New continental crust would have resulted in chemical weathering. This weathering would pull CO2 out of the atmosphere, cooling the planet through the reduction in greenhouse effect.

Causes and effects
See also: Great Oxidation Event

Before the Huronian Ice Age, most organisms were anaerobic, but around this time, the cyanobacteria evolved oxygenic photosynthesis. These bacteria were able to reproduce at exponential rates due to their new ecological niche, exploiting the abundant energy of the sunlight. Their photosynthesis produced oxygen as a waste product expelled into the air. At first, most of this oxygen was absorbed through the oxidation of surface iron and the decomposition of life forms. However, as the population of the cyanobacteria continued to grow, these oxygen sinks became saturated.[10]

As oxygen "polluted" the atmosphere and oxidised methane, a mass extinction occurred of most life forms, which were anaerobic and to whom oxygen was toxic. Methane's fraction of the atmosphere was reduced to trace gas levels, as it was oxidised into carbon dioxide and water. A different atmosphere emerged which was thinner, with less powerful greenhouse gases. Despite water's efficacy as a greenhouse gas, it readily precipitates out of the air. Earth's temperature dropped, partly because solar luminosity was lower at that time so the Earth was more vulnerable to a decline in greenhouse gases.[6]

See also

References
  1. Tang, Haoshu; Chen, Yanjing (1 September 2013). "Global glaciations and atmospheric change at ca. 2.3 Ga". Geoscience Frontiers. 4 (5): 583–596. doi:10.1016/j.gsf.2013.02.003.
  2. https://ngmdb.usgs.gov/Info/NACSN/05_1547.pdf
  3. Bekker, Andrey (2020), Gargaud, Muriel; Irvine, William M.; Amils, Ricardo; Claeys, Philippe (eds.), "Huronian Glaciation", Encyclopedia of Astrobiology, Berlin, Heidelberg: Springer, pp. 1–9, doi:10.1007/978-3-642-27833-4_742-5, ISBN 978-3-642-27833-4, retrieved 16 March 2022
  4. EPA.gov page "Understanding Global Warming Potentials"
  5. "Geologists uncover ancient mass extinction from 2 billion years ago". 5 September 2019.
  6. Plait, Phil (28 July 2014). "When a Species Poisons an Entire Planet". Slate Magazine. Retrieved 16 March 2022.
  7. Coleman, A. P. (1 March 1907). "A lower Huronian ice age". American Journal of Science. s4-23 (135): 187–192. Bibcode:1907AmJS...23..187C. doi:10.2475/ajs.s4-23.135.187. ISSN 0002-9599.
  8. Bekker, Andrey (2014). "Huronian Glaciation". Encyclopedia of Astrobiology. pp. 1–8. doi:10.1007/978-3-642-27833-4_742-4. ISBN 978-3-642-27833-4.
  9. Eyles, Nicholas; Young, Grant (1994). Deynoux, M.; Miller, J.M.G.; Domack, E.W.; Eyles, N.; Fairchild, I.J.; Young, G.M. (eds.). Geodynamic controls on glaciation in Earth history, in Earth's Glacial Record. Cambridge: Cambridge University Press. pp. 3–5. ISBN 978-0-521-54803-8.
  10. Kopp, Robert (14 June 2005). "The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis". PNAS. 102 (32): 11131–6. Bibcode:2005PNAS..10211131K. doi:10.1073/pnas.0504878102. PMC 1183582. PMID 16061801.
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