The Huronian glaciation (or Makganyene glaciation) was a glaciation that extended from 2400 million years ago to 2100 million years ago, 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.
It is the oldest known ice age, occurring at a time when in biological sense, only simple, unicellular life existed on Earth.
It is possible that there were multiple contributing factors.
As Solar radiation was notably less intense at the time, surface temperatures on Earth were above the freezing point of water primarily because of the greenhouse effect produced by high levels of atmospheric methane. The Huronian glaciation occurred at around the time that aerobic organisms evolved, the Great Oxygenation Event. This rise of oxygen resulted in the elimination of methane in the atmosphere, which in turn could have led to decreased temperatures.
Drawdown of atmospheric carbon dioxide, also a greenhouse gas (albeit weaker), has also been suggested. CO2 levels could have been reduced due to increased silicate weathering of fresh basaltic surfaces or due to a 250 million year lull in volcanic activity reducing the amount of CO2 released thereby.
Finally, the placement of the continental landmasses (a probable cause of the Cryogenian glaciation), and the Earth's orbit around the Sun may have been contributing factors.
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