Cryogenian | ||||||||||||||||||||
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Chronology | ||||||||||||||||||||
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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.[4] | |||||||||||||||||||
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°19′53″S 138°38′00″E / 31.3314°S 138.6334°E | |||||||||||||||||||
Upper GSSP ratified | March 2004[5] | |||||||||||||||||||
Atmospheric and climatic data | ||||||||||||||||||||
Mean atmospheric O2 content | c. 12 vol % (55 % of modern) | |||||||||||||||||||
Mean atmospheric CO2 content | c. 1300 ppm (5 times pre-industrial) | |||||||||||||||||||
Mean surface temperature | c. 5 °C (8.5 °C below pre-industrial) |
−4500 — – — – −4000 — – — – −3500 — – — – −3000 — – — – −2500 — – — – −2000 — – — – −1500 — – — – −1000 — – — – −500 — – — – 0 — |
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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.[6] It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
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 planet in a state known as a snowball Earth. After 70 million years it ended, but was quickly followed by the global Marinoan glaciation. There is controversy over whether these glaciations covered the entire planet, or if a band of open sea survived near the equator (slushball Earth).
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