Varanger glaciation
| Cryogenian | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 A map of the world as it appeared at the start of the Cryogenian, c. 720 Ma[1] | ||||||||||||||||||||
| Chronology | ||||||||||||||||||||
| ||||||||||||||||||||
| 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.[5] | |||||||||||||||||||
| Lower boundary GSSP candidate section(s) | To be determined | |||||||||||||||||||
| Upper boundary definition |
| |||||||||||||||||||
| 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[6] | |||||||||||||||||||
| 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 — |
| |||||||||||||||||||||||||||||||||||||||||||||
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.[7] 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.
Ratification
[edit]The Cryogenian Period was ratified in 1990 by the International Commission on Stratigraphy.[8] In contrast to most other time periods, the beginning of the Cryogenian is not linked to a globally observable and documented event. Instead, the base of the period is defined by a fixed rock age, that was originally set at 850 million years,[9] but changed in 2015 to 720 million years.[7]
This could cause ambiguity because estimates of rock age are subject to variable interpretation and laboratory error. For instance, the time scale of the Cambrian Period is not reckoned by rock younger than a given age (538.8 million years), but by the appearance of the worldwide Treptichnus pedum diagnostic trace fossil assemblages, which can be recognized in the field without extensive lab testing.[10]
Currently, there is no consensus on what global event is a suitable candidate to mark the start of the Cryogenian Period, but a global glaciation would be a likely candidate.[9]
Climate
[edit]The name of the geologic period refers to the very cold global climate of the Cryogenian.
Characteristic glacial deposits indicate that Earth suffered the most severe ice ages in its history during this period (Sturtian and Marinoan). According to Eyles and Young, "Late Proterozoic glaciogenic deposits are known from all the continents. They provide evidence of the most widespread and long-ranging glaciation on Earth." Several glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers reaching sea level in low paleolatitudes.[11]
Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.[12]
The Cryogenian is generally considered to be divisible into at least two major worldwide glaciations. The Sturtian glaciation persisted from 720 to 660 million years ago, and the Marinoan glaciation which ended approximately 635 Ma, at the end of the Cryogenian.[13] The deposits of glacial tillite also occur in places that were at low latitudes during the Cryogenian, a phenomenon which led to the hypothesis of deeply frozen planetary oceans called "Snowball Earth".[14] Between the Sturtian and Marinoan glaciations was a so-called "Cryogenian interglacial period" marked by relatively warm climate and anoxic oceans,[15] along with marine transgression.[16]
- ^ Long, Jie; Zhang, Shixi; Luo, Kunli (2019-04-29). "Cryogenian magmatic activity and early life evolution". Scientific Reports. 9 (1): 6586. doi:10.1038/s41598-019-43177-8. ISSN 2045-2322.
- ^ 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.
- ^ a b "Chart". International Commission on Stratigraphy. Archived from the original on 13 January 2017. Retrieved 14 February 2017.
- ^ Plumb, Kenneth A. (1991). "New Precambrian time scale" (PDF). Episodes. 2. 14 (2): 134–140. doi:10.18814/epiiugs/1991/v14i2/005. Retrieved 7 September 2013.
- ^ a b "GSSP Table - Precambrian". Geologic Timescale Foundation. Retrieved 7 September 2013.
- ^ Long, Jie; Zhang, Shixi; Luo, Kunli (2019-04-29). "Cryogenian magmatic activity and early life evolution". Scientific Reports. 9 (1): 6586. doi:10.1038/s41598-019-43177-8. ISSN 2045-2322.
- ^ Eyles, Nicholas; Young, Grant (1994). Deynoux, M.; Miller, J.M.G.; Domack, E.W.; Eyles, N.; Fairchild, I.J.; Young, G.M. (eds.). Geodynamic controls on glaciation in Earth history, in Earth's Glacial Record. Cambridge: Cambridge University Press. pp. 5–10. ISBN 0521548039.
- ^ Dave Lawrence (2003). "Microfossil lineages support sloshy snowball Earth". Geotimes.
- ^ Shields, G. A. (2008). "Palaeoclimate: Marinoan meltdown". Nature Geoscience. 1 (6): 351–353. Bibcode:2008NatGe...1..351S. doi:10.1038/ngeo214.
- ^ Hoffman, P.F. 2001. Snowball Earth theory
- ^ Xu, Lingang; Frank, Anja B.; Lehmann, Bernd; Zhu, Jianming; Mao, Jingwen; Ju, Yongze; Frei, Robert (21 October 2019). "Subtle Cr isotope signals track the variably anoxic Cryogenian interglacial period with voluminous manganese accumulation and decrease in biodiversity". Scientific Reports. 9 (1): 15056. Bibcode:2019NatSR...915056X. doi:10.1038/s41598-019-51495-0. ISSN 2045-2322. PMC 6803686. PMID 31636318.
- ^ Freitas, B.T.; Rudnitzki, I.D.; Morais, L.; Campos, M.D.R.; Almeida, R.P.; Warren, L.V.; Boggiani, P.C.; Caetano-Filho, S.; Bedoya-Rueda, C.; Babinski, M.; Fairchild, T.R.; Trindade, R.I.F. (30 August 2021). "Cryogenian glaciostatic and eustatic fluctuations and massive Marinoan-related deposition of Fe and Mn in the Urucum District, Brazil". Geology. 49 (12): 1478–1483. Bibcode:2021Geo....49.1478F. doi:10.1130/G49134.1. ISSN 0091-7613. S2CID 239629114. Retrieved 11 September 2023.