Huronian glaciation

The Huronian glaciation (or Makganyene glaciation) was a that  extended from 2.4 billion years ago (Gya) to 2.1 Gya, during the  and  periods of the  era. The Huronian glaciation followed the (GOE), a time when increased atmospheric oxygen decreased. The oxygen combined with the methane to form carbon dioxide and water, which do not retain heat as well as methane does.

It is the oldest and longest, occurring at a time when only simple, unicellular life existed on Earth. This ice age led to a on Earth.

Discovery and name
In 1907, first inferred a "lower Huronian ice age" from analysis of a geological formation near. This formation consists of two non-glacial deposits found between three horizons of glacial deposits of the, deposited between 2.5 and 2.2 billion years ago.

Other evidence
The  (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 (2.1–2 Gya), the (2.6–1.6 Gya),,  (2.1 Gya) and Wyoming. Similar age deposits occur in the (2.3 Gya), India (1.8 Gya) and Australia (2.5—2.0 Gya).

Geological context
The was one of a. New would have resulted in. This weathering would pull CO2 out of the atmosphere, cooling the planet through the reduction in greenhouse effect.

Causes and effects
Before the Huronian Ice Age, most organisms were, but around this time, the 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 of surface iron and the decomposition of life forms. However, as the population of the cyanobacteria continued to grow, these oxygen sinks became saturated.

As oxygen "polluted" the mostly methane atmosphere, a mass extinction occurred of most life forms, which were anaerobic and to whom oxygen was toxic. Methane turned from dominant in the atmosphere to a trace gas, as it was oxidized into carbon dioxide and water. A different atmosphere emerged which was thinner, with less powerful es. Earth's temperature dropped, partly because was lower  at that time so the Earth was more vulnerable to a decline in greenhouse gases. The Huronian Ice Age is thought to be the first time, and to have practically stopped photosynthesis.