Cryogenian
The Cryogenian (from Ancient Greek: κρύος, romanized: krýos, meaning "cold" and γένεσις, romanized: génesis, meaning "birth") is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
| Cryogenian | ||||||||||||||||||||
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A map of the world as it appeared at the start of the Cryogenian, c. 720 Ma | ||||||||||||||||||||
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| Etymology | ||||||||||||||||||||
| Name formality | Formal | |||||||||||||||||||
| Name ratified | 1990 | |||||||||||||||||||
| Usage information | ||||||||||||||||||||
| Celestial body | Earth | |||||||||||||||||||
| Regional usage | Global (ICS) | |||||||||||||||||||
| Time scale(s) used | ICS Time Scale | |||||||||||||||||||
| Definition | ||||||||||||||||||||
| Chronological unit | Period | |||||||||||||||||||
| Stratigraphic unit | System | |||||||||||||||||||
| Time span formality | Formal | |||||||||||||||||||
| Lower boundary definition | Defined chronometrically with an interim calibrated age of c. 720 Ma. GSSP is in progress. | |||||||||||||||||||
| Lower boundary definition candidates | The first appearance of widespread glaciation. | |||||||||||||||||||
| Lower boundary GSSP candidate section(s) | To be determined | |||||||||||||||||||
| Upper boundary definition |
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| Upper boundary GSSP | Enorama Creek section, Flinders Ranges, South Australia 31.3314°S 138.6334°E | |||||||||||||||||||
| Upper GSSP ratified | March 2004 | |||||||||||||||||||
| Atmospheric and climatic data | ||||||||||||||||||||
| Mean atmospheric O2 content | c. 12 vol % (60 % of modern) | |||||||||||||||||||
| Mean atmospheric CO2 content | c. 1300 ppm (5 times pre-industrial) | |||||||||||||||||||
| Mean surface temperature | c. 5 °C (9 °C below modern) | |||||||||||||||||||
−4500 — – — – −4000 — – — – −3500 — – — – −3000 — – — – −2500 — – — – −2000 — – — – −1500 — – — – −1000 — – — – −500 — – — – 0 — |
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The Cryogenian was a time of drastic biosphere changes. After the previous Boring Billion years of stability, at the beginning of Cryogenian the severe Sturtian glaciation began, freezing the entire Earth in a planetary state known as a Snowball Earth. After 70 million years it ended, but was quickly followed by the Marinoan glaciation, which was also a global event. These events are the subject of much scientific controversy specifically over whether these glaciations covered the entire planet or a band of open sea survived near the equator (termed "slushball Earth").