Editing Snowball Earth (section)

==Scientific dispute==
The argument against the hypothesis is evidence of fluctuation in ice cover and melting during "snowball Earth" deposits. Evidence for such melting comes from evidence of glacial dropstones,<ref name=Condon2002/> geochemical evidence of climate cyclicity,<ref name="Rieu"/> and interbedded glacial and shallow marine sediments.<ref name=Young1999/> A longer record from Oman, constrained to 13°N, covers the period from 712 to 545 million years ago—a time span containing the [[Cryogenian|Sturtian and Marinoan]] glaciations—and shows both glacial and ice-free deposition.<ref name=Kilner2005>{{cite journal
| author = Kilner, B. |author2=Niocaill, C.M. |author3=Brasier, M.
| year = 2005
| title = Low-latitude glaciation in the Neoproterozoic of Oman
| journal = [[Geology (journal)|Geology]]
| volume = 33
| issue = 5
| pages = 413–6
| doi = 10.1130/G21227.1
|bibcode = 2005Geo....33..413K }}</ref> The snowball Earth hypothesis does not explain the alternation of glacial and interglacial events, nor the oscillation of glacial sheet margins.<ref name="Chumakov2008">{{cite journal |last1=Chumakov |first1=N. M. |year=2008 |title=A problem of Total Glaciations on the Earth in the Late Precambrian |journal=Stratigraphy and Geological Correlation |volume=16 |issue=2 |pages=107–119 |bibcode=2008SGC....16..107C |doi=10.1134/S0869593808020019 |s2cid=129280178}}</ref>

There have been difficulties in recreating a snowball Earth with [[global climate model]]s. Simple GCMs with mixed-layer oceans can be made to freeze to the equator; a more sophisticated model with a full dynamic ocean (though only a primitive sea ice model) failed to form sea ice to the equator.<ref name=Poulsen2001>{{cite journal
| author = Poulsen, C.J. |author2=Pierrehumbert, R.T. |author3=Jacob, R.L.
| year = 2001
| title = Impact of ocean dynamics on the simulation of the Neoproterozoic ''snowball Earth''
| journal = [[Geophysical Research Letters]]
| volume = 28
| issue = 8
| pages = 1575–8
| doi = 10.1029/2000GL012058
| bibcode=2001GeoRL..28.1575P
|s2cid=2190435 | doi-access = free
}}</ref> In addition, the levels of {{co2}} necessary to melt a global ice cover have been calculated to be 130,000 ppm,<ref name=Crowley2001/> which is considered by some to be unreasonably large.<ref>{{cite journal |last1=Bao |first1=Huiming |last2=Lyons |first2=J. R. |last3=Zhou |first3=Chuanming |title=Triple oxygen isotope evidence for elevated CO2 levels after a Neoproterozoic glaciation |journal=[[Nature (journal)|Nature]] |date=22 May 2008 |volume=453 |issue=7194 |pages=504–506 |doi=10.1038/nature06959 |pmid=18497821 |bibcode=2008Natur.453..504B |s2cid=205213330 }}</ref>

Strontium isotopic data have been found to be at odds with proposed snowball Earth models of silicate weathering shutdown during glaciation and rapid rates immediately post-glaciation. Therefore, methane release from permafrost during [[marine transgression]] was proposed to be the source of the large measured carbon excursion in the time immediately after glaciation.<ref name=Kennedy2001>{{cite journal |last1=Kennedy |first1=Martin J. |last2=Christie-Blick |first2=Nicholas |last3=Sohl |first3=Linda E. |title=Are Proterozoic cap carbonates and isotopic excursions a record of gas hydrate destabilization following Earth's coldest intervals? |journal=[[Geology (journal)|Geology]] |year=2001 |volume=29 |issue=5 |pages=443 |doi=10.1130/0091-7613(2001)029<0443:APCCAI>2.0.CO;2 |bibcode=2001Geo....29..443K }}</ref>

==="Zipper rift" hypothesis===
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Nick Eyles suggests that the Neoproterozoic Snowball Earth was in fact no different from any other glaciation in Earth's history, and that efforts to find a single cause are likely to end in failure.<ref name=Eyles2004 /> The "zipper rift" hypothesis proposes two pulses of continental "unzipping"—first, the breakup of Rodinia, forming the proto-Pacific Ocean; then the splitting of the continent [[Baltica]] from [[Laurentia]], forming the proto-Atlantic—coincided with the glaciated periods.
The associated tectonic uplift would form high plateaus, just as the [[East African Rift]] is responsible for high topography; this high ground could then host glaciers.

Banded iron formations have been taken as unavoidable evidence for global ice cover, since they require dissolved iron ions and anoxic waters to form; however, the limited extent of the Neoproterozoic banded iron deposits means that they may have formed in inland seas rather than in frozen oceans. Such seas can experience a wide range of chemistries; high rates of evaporation could concentrate iron ions, and a periodic lack of circulation could allow anoxic bottom water to form. Continental rifting, with associated subsidence, tends to produce such landlocked water bodies. This rifting, and associated subsidence, would produce the space for the fast deposition of sediments, negating the need for an immense and rapid melting to raise the global sea levels.

===High-obliquity hypothesis===
A competing hypothesis to explain the presence of ice on the equatorial continents was that Earth's [[axial tilt]] was quite high, in the vicinity of 60°, which would place Earth's land in high "latitudes", although supporting evidence is scarce.<ref>{{cite web
| url= http://www.livescience.com/7105-day-earth-fell.html
| title= LiveScience.com: The Day The Earth Fell Over| website= [[Live Science]]| date= 25 August 2006}}</ref> A less extreme possibility would be that it was merely Earth's magnetic pole that wandered to this inclination, as the magnetic readings which suggested ice-filled continents depend on the magnetic and rotational poles being relatively similar. In either of these two situations, the freeze would be limited to relatively small areas, as is the case today; severe changes to Earth's climate are not necessary.

===Inertial interchange true polar wander===
The evidence for low-latitude glacial deposits during the supposed snowball Earth episodes has been reinterpreted via the concept of inertial interchange [[true polar wander]].<ref name=Kirschvink1997>{{cite journal
| author = Kirschvink, J.L.
|author2=Ripperdan, R.L. |author3=Evans, D.A. 
| date = 25 July 1997
| title = Evidence for a Large-Scale Reorganization of Early Cambrian Continental Masses by Inertial Interchange True Polar Wander
| journal = [[Science (journal)|Science]]
| volume = 277
| issue = 5325
| pages = 541–545
| doi = 10.1126/science.277.5325.541
|s2cid=177135895 }}</ref><ref name=Meert1999>{{cite journal
| author = Meert, J.G.
| year = 1999
| title = A palaeomagnetic analysis of Cambrian true polar wander
| journal = [[Earth and Planetary Science Letters]]
| volume = 168
| issue = 1–2
| pages = 131–144
| doi = 10.1016/S0012-821X(99)00042-4
| bibcode=1999E&PSL.168..131M
}}</ref>
This hypothesis, created to explain palaeomagnetic data, suggests that Earth's orientation relative to its axis of rotation shifted one or more times during the general time-frame attributed to snowball Earth. This could feasibly produce the same distribution of glacial deposits without requiring any of them to have been deposited at equatorial latitude.<ref>{{cite web |url=http://www.pppl.gov/colloquia_pres/WC01OCT08_Maloof.pdf |title= Rock magnetic evidence for rapid motion of the solid Earth with respect to its spin axis |year= 2008 |access-date=2010-05-13 |url-status=dead |archive-url=https://web.archive.org/web/20110607213103/http://www.pppl.gov/colloquia_pres/WC01OCT08_Maloof.pdf |archive-date=7 June 2011}}</ref> While the physics behind the proposition is sound, the removal of one flawed data point from the original study rendered the application of the concept in these circumstances unwarranted.<ref name=Torsvik1998>{{cite journal
| author = Torsvik, T.H.
| date = 2 January 1998
| title = Polar Wander and the Cambrian
| journal = [[Science (journal)|Science]]
| volume = 279
| issue = 5347
| page = 9
| doi = 10.1126/science.279.5347.9a
|bibcode = 1998Sci...279....9T | doi-access = free
}}</ref>