Editing Snowball Earth (section)

===Cyclic climate fluctuations===
Using the ratio of mobile [[cation]]s to those that remain in soils during chemical weathering (the chemical index of alteration), it has been shown that chemical weathering varied in a cyclic fashion within a glacial succession, increasing during interglacial periods and decreasing during cold and arid glacial periods.<ref name="Rieu">{{cite journal
|author1=R. Rieu |author2=P.A. Allen |author3=M. Plötze |author4=T. Pettke | title=Climatic cycles during a Neoproterozoic "snowball" glacial epoch
| journal=Geology
| year=2007
| volume=35
| issue=4
| pages=299–302
| doi = 10.1130/G23400A.1|bibcode = 2007Geo....35..299R }}</ref> This pattern, if a true reflection of events, suggests that the "snowball Earths" bore a stronger resemblance to [[Timeline of glaciation#Nomenclature of Quaternary glacial cycles|Pleistocene]] [[ice age]] cycles than to a completely frozen Earth.

In addition, glacial sediments of the [[Port Askaig Tillite Formation]] in Scotland clearly show interbedded cycles of glacial and shallow marine sediments.<ref name=Young1999>{{cite journal
| author = Young, G.M.
| year = 1999
| title = Some aspects of the geochemistry, provenance and palaeoclimatology of the Torridonian of NW Scotland
| journal = Journal of the Geological Society
| volume = 156
| issue = 6
| pages = 1097–1111
| doi = 10.1144/gsjgs.156.6.1097
| bibcode = 1999JGSoc.156.1097Y
| s2cid = 128600222
}}</ref> The significance of these deposits is highly reliant upon their dating. Glacial sediments are difficult to date, and the closest dated bed to the Port Askaig group is 8&nbsp;km stratigraphically above the beds of interest. Its dating to 600&nbsp;Ma means the beds can be tentatively correlated to the Sturtian glaciation, but they may represent the advance or retreat of a snowball Earth.