Editing Cryogenian

{{short description|Second period of the Neoproterozoic Era, with major glaciation}}
{{Infobox geologic timespan
| name                         = Cryogenian
| color                        = Cryogenian
| top_bar                      = all time
| time_start                   = 720
| time_start_prefix            = c.{{space}}
| time_end                     = 635
| time_end_prefix              = c.{{space}}
| image_map                    = Mollweide Paleographic Map of Earth, 690 Ma (Cryogenian Period).png
| caption_map                  = A map of Earth as it appeared during the early Cryogenian, {{circa}} 690 Ma
| image_outcrop                =
| caption_outcrop              =
| image_art                    =
| caption_art                  =
<!--Chronology--> 
| timeline                     = Cryogenian
<!--Etymology-->
| name_formality               = Formal
| name_accept_date             = 1990
| alternate_spellings          =
| synonym1                     =
| synonym1_coined              =
| synonym2                     =
| synonym2_coined              =
| synonym3                     =
| synonym3_coined              =
| nicknames                    =
| former_names                 =
| proposed_names               =
<!--Usage Information-->
| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
<!--Definition-->
| chrono_unit                  = Period
| strat_unit                   = System
| proposed_by                  =
| timespan_formality           = Formal
| lower_boundary_def           = Defined chronometrically with an interim calibrated age of c. 720 Ma. GSSP is in progress.
| lower_def_candidates         =  The first appearance of widespread glaciation.<ref name="Shields-Zhou-2016">{{cite journal|last1=Shields-Zhou|first1=Graham A.|last2=Porter|first2=Susannah|last3=Halverson|first3=Galen P.|title=A new rock-based definition for the Cryogenian Period (circa 720 – 635 Ma)|journal=Episodes|volume=39|issue=1|year=2016|pages=3–8|issn=0705-3797|doi=10.18814/epiiugs/2016/v39i1/89231|doi-access=free |url=https://discovery.ucl.ac.uk/id/eprint/1496826/1/Shields-Zhou%20et%20al%20%282016%29%20Cryogenian%20Period.pdf}}</ref>
| lower_gssp_candidates        = To be determined
| upper_boundary_def           =
* Worldwide distinct cap carbonates.
* Beginning of a distinctive pattern of secular changes in [[carbon isotope]]s.
| upper_gssp_location          = Enorama Creek section, [[Flinders Ranges]], [[South Australia]]
| upper_gssp_coords            = {{Coord|31.3314|S|138.6334|E|display=inline}}
| upper_gssp_accept_date       = March 2004<ref>{{cite journal |last1=Knoll |first1=Andrew H. |last2=Walter |first2=Malcolm R. |last3=Narbonne |first3=Guy M. |last4=Christie-Black |first4=Nicholas |title=The Ediacaran Period: a new addition to the geologic time scale |journal=Lethaia |date=3 March 2006 |volume=39 |issue=1 |pages=13–30 |doi=10.1080/00241160500409223 |bibcode=2006Letha..39...13K |url=https://stratigraphy.org/gssps/files/ediacaran.pdf |access-date=6 December 2020}}</ref>
<!--Atmospheric and Climatic Data-->
| o2                           = 12
| co2                          = 1300
| temp                         = 5
| sea_level                    =
}}
{{Life timeline}}
The '''Cryogenian''' (from {{langx|grc|κρύος|krýos}}, meaning "cold" and {{lang|grc|γένεσις}}, <small>romanized:</small> {{Transliteration|grc|génesis}}, meaning "birth") is a [[geologic period]] that lasted from {{Mya|720 |635}}.<ref name="ICS" /> 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 change]]s. 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 Earth|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 sheet]]s blocking off [[sunlight]] would nevertheless have significantly hindered [[primary production]] in the [[shallow sea]]s and caused major [[mass extinction]]s and [[biosphere]] turnovers.

==Ratification==
The Cryogenian Period was ratified in 1990 by the [[International Commission on Stratigraphy]].<ref name="Plumb-1991">{{cite journal |last=Plumb |first=Kenneth A. |title=New Precambrian time scale |journal=Episodes |year=1991 |volume=14 |series=2 |issue=2 |pages=134–140 |doi=10.18814/epiiugs/1991/v14i2/005 |access-date=7 September 2013 |url=http://www.stratigraphy.org/bak/Precambrian.pdf |doi-access=free }}</ref> 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&nbsp;million years,<ref name="GSSPTable">{{cite web |title=GSSP Table - Precambrian |url=https://engineering.purdue.edu/Stratigraphy/gssp/index.php?parentid=181 |publisher=Geologic Timescale Foundation |access-date=7 September 2013}}</ref> but changed in 2015 to 720&nbsp;million years.<ref name="ICS">{{cite web |url=http://www.stratigraphy.org/index.php/ics-chart-timescale |title=Chart |publisher=International Commission on Stratigraphy |access-date=2017-02-14 |url-status=dead |archive-url=https://web.archive.org/web/20170113013553/http://www.stratigraphy.org/index.php/ics-chart-timescale |archive-date=2017-01-13 |df=dmy-all}}</ref>

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 ({{Period start|Cambrian}} 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.<ref>{{Cite journal |last1=Sanchez |first1=Evelyn A. M. |last2=Uhlein |first2=Alexandre |last3=Fairchild |first3=Thomas R. |date=2021-01-01 |title=Treptichnus pedum in the Três Marias Formation, south-central Brazil, and its implications for the Ediacaran-Cambrian transition in South America |url=https://www.sciencedirect.com/science/article/abs/pii/S0895981120305265 |journal=Journal of South American Earth Sciences |volume=105 |pages=102983 |doi=10.1016/j.jsames.2020.102983 |bibcode=2021JSAES.10502983S |issn=0895-9811|url-access=subscription }}</ref>

Currently, there is no consensus on what global event is a suitable candidate to mark the start of the Cryogenian Period, but a [[ice age|global glaciation]] would be a likely candidate.<ref name="GSSPTable" />

==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.<ref name="Eyles-1994">{{cite book|last1=Eyles|first1=Nicholas|last2=Young|first2=Grant|editor1-last=Deynoux|editor1-first=M.|editor2-last=Miller|editor2-first=J.M.G.|editor3-last=Domack|editor3-first=E.W.|editor4-last=Eyles|editor4-first=N.|editor5-last=Fairchild|editor5-first=I.J.|editor6-last=Young|editor6-first=G.M.|editor-link3=Eugene Domack|title=Geodynamic controls on glaciation in Earth history, in Earth's Glacial Record|date=1994|publisher=Cambridge University Press|location=Cambridge|isbn=0521548039|pages=[https://archive.org/details/earthsglacialrec0000unse/page/5 5–10]|url=https://archive.org/details/earthsglacialrec0000unse/page/5}}</ref>

[[Glacier]]s extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.<ref>{{cite web |title = Microfossil lineages support sloshy snowball Earth |author = Dave Lawrence |year = 2003 |publisher = Geotimes |url = http://www.agiweb.org/geotimes/apr03/WebExtra041803.html}}</ref>

[[File:Elatina Fm diamictite.JPG|thumb|[[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.<ref>{{Cite journal | last1 = Shields | first1 = G. A. | title = Palaeoclimate: Marinoan meltdown | doi = 10.1038/ngeo214 | journal = Nature Geoscience | volume = 1 | issue = 6 | pages = 351–353 | year = 2008 |bibcode = 2008NatGe...1..351S }}</ref> 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]]".<ref>Hoffman, P.F. 2001. [http://www.snowballearth.org ''Snowball Earth theory'']</ref> Between the Sturtian and Marinoan glaciations was a so-called "Cryogenian interglacial period" marked by relatively warm climate and [[Anoxic event|anoxic oceans]],<ref name="Xu-2019">{{Cite journal |last1=Xu |first1=Lingang |last2=Frank |first2=Anja B. |last3=Lehmann |first3=Bernd |last4=Zhu |first4=Jianming |last5=Mao |first5=Jingwen |last6=Ju |first6=Yongze |last7=Frei |first7=Robert |date=21 October 2019 |title=Subtle Cr isotope signals track the variably anoxic Cryogenian interglacial period with voluminous manganese accumulation and decrease in biodiversity |journal=[[Scientific Reports]] |language=en |volume=9 |issue=1 |page=15056 |doi=10.1038/s41598-019-51495-0 |issn=2045-2322 |pmc=6803686 |pmid=31636318 |bibcode=2019NatSR...915056X }}</ref> along with marine transgression.<ref>{{Cite journal |last1=Freitas |first1=B.T. |last2=Rudnitzki |first2=I.D. |last3=Morais |first3=L. |last4=Campos |first4=M.D.R. |last5=Almeida |first5=R.P. |last6=Warren |first6=L.V. |last7=Boggiani |first7=P.C. |last8=Caetano-Filho |first8=S. |last9=Bedoya-Rueda |first9=C. |last10=Babinski |first10=M. |last11=Fairchild |first11=T.R. |last12=Trindade |first12=R.I.F. |date=30 August 2021 |title=Cryogenian glaciostatic and eustatic fluctuations and massive Marinoan-related deposition of Fe and Mn in the Urucum District, Brazil |url=https://pubs.geoscienceworld.org/geology/article/49/12/1478/607268/Cryogenian-glaciostatic-and-eustatic-fluctuations |journal=[[Geology (journal)|Geology]] |language=en |volume=49 |issue=12 |pages=1478–1483 |doi=10.1130/G49134.1 |bibcode=2021Geo....49.1478F |hdl=11449/222880 |s2cid=239629114 |issn=0091-7613 |access-date=11 September 2023}}</ref>

== Paleogeography ==
{{main|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]].<ref>{{Cite journal |last1=Nance |first1=R. Damian |last2=Evans |first2=David A. D. |last3=Murphy |first3=J. Brendan |date=2022-09-01 |title=Pannotia: To be or not to be? |url=https://www.sciencedirect.com/science/article/pii/S0012825222002124 |journal=Earth-Science Reviews |volume=232 |pages=104128 |doi=10.1016/j.earscirev.2022.104128 |bibcode=2022ESRv..23204128N |issn=0012-8252|url-access=subscription }}</ref>

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 [[Myr|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.<ref name="Eyles-1994"/> The Sturtian and Marinoan are local divisions within the [[Adelaide Rift Complex]].<ref>{{Cite journal |last1=Haines |first1=Peter W. |last2=Turner |first2=Simon P. |last3=Kelley |first3=Simon P. |last4=Wartho |first4=Jo-Anne |last5=Sherlock |first5=Sarah C. |date=2004-11-15 |title=40Ar–39Ar dating of detrital muscovite in provenance investigations: a case study from the Adelaide Rift Complex, South Australia |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X04005230 |journal=Earth and Planetary Science Letters |volume=227 |issue=3 |pages=297–311 |doi=10.1016/j.epsl.2004.08.020 |issn=0012-821X|url-access=subscription }}</ref>

== Cryogenian biota and fossils ==
Between the Sturtian and Marinoan glaciations, global biodiversity was very low.<ref name="Xu-2019" />

Fossils of [[test (biology)|testate]] amoeba (or [[Arcellinida]]) first appear during the Cryogenian Period.<ref>{{cite journal |title = Testate amoeba in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon |author1=Porter, S.A. |author2=Knoll, A.H.  |name-list-style=amp |year = 2000 |journal = Paleobiology |volume = 26 |issue = 3 |pages = 360–385 |doi = 10.1666/0094-8373(2000)026<0360:TAITNE>2.0.CO;2 |bibcode=2000Pbio...26..360P |s2cid=54636062 |issn = 0094-8373|url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:3708936 |url-access = subscription }}</ref> Since 2009, some researchers have argued that during the Cryogenian Period, potentially the oldest known fossils of [[sponges]], and therefore [[animals]], were formed.<ref>{{cite journal |title = Fossil steroids record the appearance of Demospongiae during the Cryogenian period |url = http://eaps.mit.edu/geobiology/recent%20pubs/Love%20et%20al%202009.pdf |author = Love |year = 2009 |journal = Nature |doi = 10.1038/nature07673 |last2 = Grosjean |first2 = Emmanuelle |last3 = Stalvies |first3 = Charlotte |last4 = Fike |first4 = David A. |last5 = Grotzinger |first5 = John P. |last6 = Bradley |first6 = Alexander S. |last7 = Kelly |first7 = Amy E. |last8 = Bhatia |first8 = Maya |last9 = Meredith |first9 = William |volume = 457 |issue = 7230 |pages = 718–721 |pmid = 19194449 |bibcode = 2009Natur.457..718L |s2cid = 4314662 |display-authors = etal |access-date = 2009-04-15 |archive-date = 2018-05-08 |archive-url = https://web.archive.org/web/20180508132248/http://eaps.mit.edu/geobiology/recent%20pubs/Love%20et%20al%202009.pdf |url-status = dead }}</ref><ref>{{cite journal|last1=Maloof|first1=Adam C.|first2=Catherine V.|last2=Rose|first3=Robert|last3=Beach|first4=Bradley M.| last4=Samuels|first5=Claire C.|last5=Calmet|first6=Douglas H.|last6=Erwin|first7=Gerald R.|last7=Poirier|first8=Nan|last8=Yao|first9=Frederik J.|last9=Simons|title=Possible animal-body fossils in pre-Marinoan limestones from South Australia|journal=Nature Geoscience|date=17 August 2010|volume=3|pages=653–659|doi=10.1038/ngeo934|issue=9|bibcode = 2010NatGe...3..653M}}</ref><ref>{{cite web |title = Discovery of possible earliest animal life pushes back fossil record |date = 2010-08-17 |url = http://www.physorg.com/news201273825.html}}</ref> 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.<ref>{{cite journal|author1=Wallace, M.W.|author2=Hood, A.v.S.|author3=Woon, E.M.S.|author4=Hoffman, K.-H.|author5=Reed, C.P.|year=2014|title=Enigmatic chambered structures in Cryogenian reefs: The oldest sponge-grade organisms?|journal=Precambrian Research|volume=255|pages=653–659|doi=10.1016/j.precamres.2014.09.020|bibcode=2014PreR..255..109W |hdl=11343/52679|hdl-access=free}}</ref> 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]], [[stramenopile]]s, [[ciliate]]s, [[dinoflagellate]]s, and testate amoeba.<ref>{{Cite web|url=http://palaeos.com/proterozoic/neoproterozoic/cryogenian/cryogenian2.html|title = Palaeos Proterozoic: Neoproterozoic: Cryogenian}}</ref>

The end of the period also saw the origin of [[heterotroph]]ic [[plankton]], which would feed on [[Unicellular organism|unicellular]] [[algae]] and [[prokaryote]]s, ending the [[bacteria]]l dominance of the oceans.<ref>[https://newatlas.com/fossil-fats-snowball-earth/58292/ Fossil fats reveal how complex life kicked off after Snowball Earth phase]</ref> The unicellular algae ([[Archaeplastida]]) went through a big bang of diversification, and their population went up by a factor of a hundred to a thousand.<ref>[https://www.sciencealert.com/this-groundbreaking-period-in-earth-s-history-gave-rise-to-the-first-animals We Finally Know Which Groundbreaking Period in Earth's History Gave Rise to The First Animals]</ref><ref>[https://www.bbc.com/news/science-environment-40948972 The algae that terraformed Earth]</ref>

==See also==
* {{annotated link|Timeline of glaciation}}

==References==
{{Reflist|colwidth=32em}}

==Further reading==
* {{cite web|title=Cryogenian Period |work=GeoWhen Database |url=http://www.stratigraphy.org/geowhen/stages/Cryogenian.html |access-date=January 5, 2006 |archive-url=https://web.archive.org/web/20051202005002/http://www.stratigraphy.org/geowhen/stages/Cryogenian.html |archive-date=December 2, 2005 |url-status=dead }}
* {{cite journal | author=James G. Ogg | title=Status on Divisions of the International Geologic Time Scale | journal=Lethaia | year=2004 | volume=37 | issue= 2| pages=183–199 | doi=10.1080/00241160410006492 | bibcode=2004Letha..37..183O }}
* {{cite journal | last=Brain | first=C. K. |author2=Prave, A. R. |author3=Hoffmann, K. H. |author4=Fallick, A. E. |author5=Herd, D. A. |author6=Sturrock, C. |author7=Young, I. |author8=Condon, D. J. |author9=Allison, S. G.  | title=The first animals: ca. 760-million-year-old sponge-like fossils from Namibia | year=2012 | journal= [[South African Journal of Science]] | volume=108 | doi=10.4102/sajs.v108i1/2.658 | pages=1–8|url=https://repository.up.ac.za/bitstream/2263/18222/1/Brain_First%282012%29.pdf |doi-access=free }}
* {{cite journal|last1=Hoffman|first1=Paul F.|last2=Abbot|first2=Dorian S.|display-authors=et al|title=Snowball Earth climate dynamics and Cryogenian geology-geobiology|journal=Science Advances|date=November 8, 2017|volume=3|issue=11|pages=e1600983|publisher=American Association for the Advancement of Science|doi=10.1126/sciadv.1600983|pmid=29134193|pmc=5677351|bibcode=2017SciA....3E0983H|s2cid=1465316|doi-access=free}}

== External links ==
* {{IMDb title|2380395|Australia: The Time Traveller's Guide (2012)}}
* {{YouTube|87hHbiWBwmY|Miracle Planet : Snowball Earth}} (2010s) BBC/CBC/NHK

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[[Category:Cryogenian| ]]
[[Category:Neoproterozoic|*02]]
[[Category:Geological periods]]
[[Category:Ice ages]]
[[Category:Glaciology]]
[[Category:Geology controversies]]
[[Category:Proterozoic geochronology]]