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.[6] It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.

Cryogenian
A map of the world as it appeared at the start of the Cryogenian, c. 720 Ma
Chronology
Etymology
Name formalityFormal
Name ratified1990
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitPeriod
Stratigraphic unitSystem
Time span formalityFormal
Lower boundary definitionDefined chronometrically with an interim calibrated age of c. 720 Ma. GSSP is in progress.
Lower boundary definition candidatesThe first appearance of widespread glaciation.[4]
Lower boundary GSSP candidate section(s)To be determined
Upper boundary definition
  • Worldwide distinct cap carbonates.
  • Beginning of a distinctive pattern of secular changes in carbon isotopes.
Upper boundary GSSPEnorama Creek section, Flinders Ranges, South Australia
31.3314°S 138.6334°E / -31.3314; 138.6334
Upper GSSP ratifiedMarch 2004[5]
Atmospheric and climatic data
Mean atmospheric O2 contentc. 12 vol %
(60 % of modern)
Mean atmospheric CO2 contentc. 1300 ppm
(5 times pre-industrial)
Mean surface temperaturec. 5 °C
(9 °C below modern)

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").

Ratification

The Cryogenian Period was ratified in 1990 by the International Commission on Stratigraphy.[7] 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,[8] but changed in 2015 to 720 million years.[6]

This could cause ambiguity because estimates of rock ages are variable and are subject to 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. This means that rocks can be recognized as Cambrian in the field, without extensive lab testing.

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.[8]

Climate

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.[9]

Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.[10]

Diamictite of the Elatina Formation in South Australia, formed during the Marinoan glaciation of the late Cryogenian

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.[11] 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".[12] Between the Sturtian and Marinoan glaciations was a so-called "Cryogenian interglacial period" marked by relatively warm climate and anoxic oceans,[13] along with marine transgression.[14]

Paleogeography
Main article: Rodinia § Geodynamics

Before the start of the Cryogenian, around 750 Ma, the cratons that made up the supercontinent Rodinia started to rift apart. The superocean Mirovia began to close while the superocean Panthalassa began to form. The cratons (possibly) later assembled into another supercontinent called Pannotia, in the Ediacaran.

Eyles and Young state, "Most Neoproterozoic glacial deposits accumulated as glacially influenced marine strata along rifted continental margins or interiors." Worldwide deposition of dolomite might have reduced atmospheric carbon dioxide. The break up along the margins of Laurentia at about 750 Ma occurs at about the same time as the deposition of the Rapitan Group in North America, contemporaneously with the Sturtian in Australia. A similar period of rifting at about 650 Ma occurred with the deposition of the Ice Brook Formation in North America, contemporaneously with the Marinoan in Australia.[9] The Sturtian and Marinoan are local divisions within the Adelaide Rift Complex.

Cryogenian biota and fossils

Between the Sturtian and Marinoan glaciations, global biodiversity was very low.[13]

Fossils of testate amoeba (or Arcellinida) first appear during the Cryogenian Period.[15] Since 2009, some researchers have argued that during the Cryogenian Period, potentially the oldest known fossils of sponges, and therefore animals, were formed.[16][17][18] However, it is unclear whether these fossils actually belong to sponges, though the authors do not rule out the possibility of such fossils to represent proto-sponges or complex microbial precursors to sponge-grade organisms.[19] The issue of whether or not biology was impacted by this event has not been settled, for example Porter (2000) suggests that new groups of life evolved during this period, including the red algae and green algae, stramenopiles, ciliates, dinoflagellates, and testate amoeba.[20]

The end of the period also saw the origin of heterotrophic plankton, which would feed on unicellular algae and prokaryotes, ending the bacterial dominance of the oceans.[21]

See also

References
  1. Arnaud, Emmanuelle; Halverson, Galen P.; Shields-Zhou, Graham Anthony (30 November 2011). "Chapter 1 The geological record of Neoproterozoic ice ages". Memoirs. Geological Society of London. 36 (1): 1–16. doi:10.1144/M36.1.
  2. 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.
  3. 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.
  4. 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.
  5. 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: 13–30. doi:10.1080/00241160500409223. Retrieved 6 December 2020.
  6. "Chart". International Commission on Stratigraphy. Archived from the original on 13 January 2017. Retrieved 14 February 2017.
  7. 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.
  8. "GSSP Table - Precambrian". Geologic Timescale Foundation. Retrieved 7 September 2013.
  9. 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.
  10. Dave Lawrence (2003). "Microfossil lineages support sloshy snowball Earth". Geotimes.
  11. Shields, G. A. (2008). "Palaeoclimate: Marinoan meltdown". Nature Geoscience. 1 (6): 351–353. Bibcode:2008NatGe...1..351S. doi:10.1038/ngeo214.
  12. Hoffman, P.F. 2001. Snowball Earth theory
  13. 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): 1–8. doi:10.1038/s41598-019-51495-0. ISSN 2045-2322. PMC 6803686. PMID 31636318. Retrieved 11 September 2023.
  14. 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. doi:10.1130/G49134.1. ISSN 0091-7613. Retrieved 11 September 2023.
  15. Porter, S.A. & Knoll, A.H. (2000). "Testate amoeba in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon". Paleobiology. 26 (3): 360–385. doi:10.1666/0094-8373(2000)026<0360:TAITNE>2.0.CO;2. ISSN 0094-8373. S2CID 54636062.
  16. Love; Grosjean, Emmanuelle; Stalvies, Charlotte; Fike, David A.; Grotzinger, John P.; Bradley, Alexander S.; Kelly, Amy E.; Bhatia, Maya; Meredith, William; et al. (2009). "Fossil steroids record the appearance of Demospongiae during the Cryogenian period" (PDF). Nature. 457 (7230): 718–721. Bibcode:2009Natur.457..718L. doi:10.1038/nature07673. PMID 19194449. S2CID 4314662. Archived from the original (PDF) on 2018-05-08. Retrieved 2009-04-15.
  17. Maloof, Adam C.; Rose, Catherine V.; Beach, Robert; Samuels, Bradley M.; Calmet, Claire C.; Erwin, Douglas H.; Poirier, Gerald R.; Yao, Nan; Simons, Frederik J. (17 August 2010). "Possible animal-body fossils in pre-Marinoan limestones from South Australia". Nature Geoscience. 3 (9): 653–659. Bibcode:2010NatGe...3..653M. doi:10.1038/ngeo934.
  18. "Discovery of possible earliest animal life pushes back fossil record". 2010-08-17.
  19. Wallace, M.W.; Hood, A.v.S.; Woon, E.M.S.; Hoffman, K.-H.; Reed, C.P. (2014). "Enigmatic chambered structures in Cryogenian reefs: The oldest sponge-grade organisms?". Precambrian Research. 255: 653–659. doi:10.1016/j.precamres.2014.09.020. hdl:11343/52679.
  20. "Palaeos Proterozoic: Neoproterozoic: Cryogenian".
  21. Fossil fats reveal how complex life kicked off after Snowball Earth phase

Further reading
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