Editing Cryogenian (section)

{{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.