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 after 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 does not retain heat as well as methane does.
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It is the oldest and longest ice age, occurring at a time when, in a biological sense, only simple, unicellular life existed on Earth. This ice age led to a mass-extinction on Earth.
Name origin
This geological era was named for two non-glacial sediment deposits found between three separate horizons of glacial deposits of the Huronian Supergroup deposited between 2.5 and 2.2 billion years ago in the geographic area of Lake Huron.
Geological context
The tectonic setting was one of a rifting continental margin. New continental crust would have resulted in chemical weathering. That coupled with reduced solar luminosity would have caused an 'antigreenhouse' effect as carbon dioxide in Earth's atmosphere was reduced. Volcanic sources in turn would have replenished that carbon dioxide, resulting in warming and interglacial periods. 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
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 sun. 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 led to a mass extinction of most life forms, which were anaerobic, as oxygen was toxic to them. As oxygen "polluted" the mostly methane atmosphere, and methane bonded with oxygen to form carbon dioxide and water, a different, thinner atmosphere emerged, and Earth began to lose heat. Thus began the Huronian Ice Age.