Varanger glaciation
| Cryogenian | ||||||||||||||||||||
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 A map of the world as it appeared at the start of the Cryogenian, c. 720 Ma[citation needed] | ||||||||||||||||||||
| 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 is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran.
The Cryogenian was a time of drastic climate changes. After the long environmental stability/stagnation during the Boring Billion, the Sturtian glaciation began at the beginning of Cryogenian, freezing the entire planet in a state of severe icehouse climate known as a snowball Earth. After 70 million years it ended, but was quickly followed by another global ice age, the Marinoan glaciation. There is controversy over whether these glaciations indeed covered the entire planet, or whether a band of open sea survived near the equator (i.e. "slushball Earth"), but the extreme climates with massive expanse of ice sheets blocking off sunlight would nevertheless have significantly hindered primary production in the shallow seas and caused major mass extinctions and biosphere turnovers.
- ^ a b Arnaud, Emmanuelle; Halverson, Galen P.; Shields-Zhou, Graham Anthony (30 November 2011). "Chapter 1 The geological record of Neoproterozoic ice ages". Memoirs. 36 (1). Geological Society of London: 1–16. doi:10.1144/M36.1.
- ^ a b Hoffman, Paul F.; Abbot, Dorian S.; Ashkenazy, Yosef; Benn, Douglas I.; Brocks, Jochen J.; Cohen, Phoebe A.; Cox, Grant M.; Creveling, Jessica R.; Donnadieu, Yannick; Erwin, Douglas H.; Fairchild, Ian J.; Ferreira, David; Goodman, Jason C.; Halverson, Galen P.; Jansen, Malte F. (2017-11-03). "Snowball Earth climate dynamics and Cryogenian geology-geobiology". Science Advances. 3 (11): e1600983. doi:10.1126/sciadv.1600983. ISSN 2375-2548. PMC 5677351. PMID 29134193.
- ^ Brocks, Jochen J. (2018-09-28). Lyons, Timothy W.; Droser, Mary L.; Lau, Kimberly V.; Porter, Susannah M. (eds.). "The transition from a cyanobacterial to algal world and the emergence of animals". Emerging Topics in Life Sciences. 2 (2): 181–190. doi:10.1042/ETLS20180039. ISSN 2397-8554.
- ^ Shields-Zhou, Graham A.; Porter, Susannah; Halverson, Galen P. (2016). "A new rock-based definition for the Cryogenian Period (circa 720 – 635 Ma)" (PDF). Episodes. 39 (1): 3–8. doi:10.18814/epiiugs/2016/v39i1/89231. ISSN 0705-3797.
- ^ Knoll, Andrew H.; Walter, Malcolm R.; Narbonne, Guy M.; Christie-Black, Nicholas (3 March 2006). "The Ediacaran Period: a new addition to the geologic time scale" (PDF). Lethaia. 39 (1): 13–30. Bibcode:2006Letha..39...13K. doi:10.1080/00241160500409223. Retrieved 6 December 2020.
- ^ Cite error: The named reference
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