Cryogenian

The Cryogenian Period which includes the Sturtian and Marinoan (formerly known as the Varanger) ice ages is the geological Period before the Ediacaran (Late Precambrian), and lasts from approximately 800Ma to 635Ma. The name is derived from the glacial deposits characteristic of the Period, indicating that at this time, the Earth was rocked by the most severe ice ages in history, with glaciers extending to the equator on several occasions. These glaciations are represented by tillite deposits in Congo, Australia, China, North America, Sahara, Oman, Ireland, Scotland, Norway, and many other locations around the world. It is generally considered to be divisible into at least two (Sturtian around 800Ma and Marinoan/Varanger 650Ma) major worldwide glaciations, with several other more localised glaciations. The tillite deposits occur also in locations which were at low latitudes during the Cryogenian, which lead to the hypothesis of Snowball Earth.

The population of acritarchs crashed during this glaciation and it is claimed that oxygen levels in the atmosphere increased after the glaciation. There are a number of enigmatic features with regard to this glaciation including indications of glaciation at very low latitudes and the presence of limestones -- normally warm water sediments above, below and intermixed with glacial deposits. Paleomagnetism seems to indicate very high continental drift rates leading some geologists to question whether some of the phenomena might be due to magnetic pole wandering (Inertial Interchange True Polar Wander - see the work of J. Kirshvink) rather than plate motion and low latitude glaciation.

Other known world wide glaciations include the Huronian from 2400Ma to 2100Ma, Andean-Saharan from 450-420Ma, the Karoo glaciation from 360Ma to 260Ma, and the Cenozoic glaciation which started 30Ma in Antarctica and are not over.