Huronian glaciation

The Huronian glaciation (or Makganyene glaciation) was a glaciation that extended from 2.4 billion years ago (Gya) to 2.1 Gya, 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. It is the oldest and longest ice age, occurring at a time when only simple, unicellular life existed on Earth. This ice age led to a mass extinction on Earth. In 1907, Arthur Philemon Coleman first inferred a 'lower Huronian ice age' from analysis of a geological formation near Lake Huron. 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 billion years ago. 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 (2.1–2 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). 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. 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. This had consequences: The Huronian Ice Age is thought to be the first time Earth was completely covered in ice, and to have practically stopped photosynthesis. 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.