The Cryogenian is a geologic period that lasted from 720 to 635 million years ago.[6] It is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran.The Cryogenian is a geologic period that lasted from 720 to 635 million years ago.[6] It is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran.