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A period of the Proterozoic eon that began 850 Ma ago and ended 630 (+5, -30) Ma ago. Its start is a fixed date and its end is defined by the termination of the Varinger (Marinoan) glaciation and a change in the 13C content of rocks. The Cryogenian followed the Tonian period and preceded the Ediacaran period.

Subjects: Earth Sciences and Geography.

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