Part of the Neoproterozoic Era
Rodinian Period - Cryogenian Period - Ediacaran Period
Rodinian Period - Cryogenian Period - Early Ediacaran Epoch
The Cryogenian Period is the first period of the Neoproterozoic Era and the fifth of the Proterozoic Eon. The Cryogenian begins with the first appearance of δ13C anomalies (δ13C is an isotopic signature measuring the ratio of Carbon-12 to Carbon-13 isotopes) and ends with the conclusion of the Marinoan glaciation. The Cryogenian includes the two largest glaciations in the planet's history, the Sturtian and the Marinoan, both of which are believed to have encompassed the entire planet (though a small minority of scientists still exists that contends that the events were only regional). These "ice ages" are reffered to as "Snowball Earths". The Sturtian glaciation lasted from 750 MYA until 700 MYA, while the Marinoan persisted from 650 MYA until 635 MYA. The supercontinent of Pannotia began to form after the breakup of the existing supercontinent of Rodinia at around 750 MYA. Testate amoebae and sponges (the first animals) first appeared during the Cryogenian.
The Cryogenian is not further subdivided into epochs.
Cryogenian Timescale:
Cryogenian Period - 850-635 MYA