The Huronian glaciation (or Makganyene glaciation) was a glaciation that extended from 2.4 billion years ago (Ga) to 2.1 Ga, during the Siderian and Rhyacian periods of the Paleoproterozoic era. The Huronian glaciation followed 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, which do not retain heat as well as methane does.
Discovery and name
This geological formation, in the geographic area of Lake Huron, 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 billion years ago.
The Gowganda formation (2.3 Ga) contains "the most widespread and most convincing glaciogenic deposits of this era", according to Eyles and Young. Similar deposits are found in Michigan (2.1–2 Ga), the Black Hills (2.6–1.6 Ga), Chibougamau, Canadian Northern Territories (2.1 Ga) and Wyoming. Similar age deposits occur in the Griquatown Basin (2.3 Ga), India (1.8 Ga) and Australia (2.5—2.0 Ga).
Causes and effects
Before the Huronian Ice Age, most organisms were anaerobic, but around this time, the cyanobacteria evolved photosynthesis. These bacteria were able to reproduce at exponential rates due to their new ecological niche, exploiting the near-limitless 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 oxidization of surface iron and the decomposition of life forms. However, as the population of the cyanobacteria continued to grow, these oxygen sinks became saturated. This had consequences:
As oxygen "polluted" the mostly methane atmosphere, a mass extinction occurred of most life forms, which were anaerobic, as oxygen was toxic to them.
Methane turned from dominant in the atmosphere to a trace gas, as it was oxidized into carbon dioxide and water. A different atmosphere emerged: thinner, with less powerful greenhouse gas, and Earth's temperature dropped (all the more so that solar luminosity was lower than now at that time). Thus began the Huronian Ice Age.
The Huronian Ice Age is thought to be Snowball Earth Episode I, and to have practically stopped photosynthesis.
Oscillations and the end of the Huronian era
These formations include interglacial periods. These interglacials, and eventually the end of the glacial era, could be the result of a build-up of carbon dioxide in Earth's atmosphere from volcanic sources, because photosynthetic consumption of this gas was below its production by out-gassing. This would result in an increased greenhouse effect, leading to warming and interglacial periods. Then photosynthesis would resume, and CO2 concentration would drop sufficiently that glaciation would occur again. Reasons why glaciation did not resume at the end of the Huronian era are still debated.
- 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.
- 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 0-521-54803-9.
- Kopp, Robert (14 June 2005). "The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis" (PDF). PNAS. 102 (32): 11131–6. doi:10.1073/pnas.0504878102. PMC . PMID 16061801. Retrieved 8 August 2016.
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