Editing Snowball Earth (section)

===Palaeomagnetism===
The snowball Earth hypothesis was first posited to explain what were then considered to be glacial deposits near the equator. Since tectonic plates move slowly over time, ascertaining their position at a given point in Earth's long history is not easy. In addition to considerations of how the recognizable landmasses could have fit together, the latitude at which a rock was deposited can be constrained by palaeomagnetism.

When [[sedimentary rock]]s form, magnetic minerals within them tend to align with [[Earth's magnetic field]]. Through the precise measurement of this palaeomagnetism, it is possible to estimate the [[latitude]] (but not the [[longitude]]) where the rock matrix was formed. Palaeomagnetic measurements have indicated that some sediments of glacial origin in the Neoproterozoic rock record were deposited within 10 degrees of the equator,<ref name="Evans">{{cite journal
| author=D.A.D. Evans
| title=Stratigraphic, geochronological, and palaeomagnetic constraints upon the Neoproterozoic climatic paradox
| journal=American Journal of Science
| year=2000
| volume=300
| issue=5
| pages=347–433
| doi = 10.2475/ajs.300.5.347| bibcode=2000AmJS..300..347E
}}</ref> although the accuracy of this reconstruction is in question.<ref name=Eyles2004 /> This palaeomagnetic location of apparently glacial sediments (such as [[dropstone]]s) has been taken to suggest that glaciers extended from land to sea level in tropical latitudes at the time the sediments were deposited. It is not clear whether this implies a global glaciation or the existence of localized, possibly land-locked, glacial regimes.<ref name=Young1995>{{cite journal
| author = Young, G.M.
| date = 1 February 1995
| title = Are Neoproterozoic glacial deposits preserved on the margins of Laurentia related to the fragmentation of two supercontinents?
| journal = Geology
| volume = 23
| issue = 2
| pages = 153–6
| doi = 10.1130/0091-7613(1995)023<0153:ANGDPO>2.3.CO;2
|bibcode = 1995Geo....23..153Y }}</ref> Others have even suggested that most data do not constrain any glacial deposits to within 25° of the equator.<ref name=Meert1994nmse>{{Cite journal| doi = 10.1016/0012-821X(94)90253-4| title = The Neoproterozoic (1000–540 Ma) glacial intervals: No more snowball earth?| year = 1994| last1 = Meert | first1 = J. G.| last2 = Van Der Voo | first2 = R.| journal = Earth and Planetary Science Letters| volume = 123| issue = 1–3| pages = 1–13| bibcode=1994E&PSL.123....1M | hdl = 2027.42/31585| hdl-access = free}}</ref>

Skeptics suggest that the palaeomagnetic data could be corrupted if Earth's ancient magnetic field was substantially different from today's. Depending on the rate of cooling of [[Internal structure of Earth|Earth's core]], it is possible that during the Proterozoic, the [[Earth's magnetic field|magnetic field]] did not approximate a simple [[dipole|dipolar]] distribution, with north and south [[Poles of astronomical bodies|magnetic poles]] roughly aligning with the planet's axis as they do today. Instead, a hotter core may have circulated more vigorously and given rise to 4, 8 or more poles. Palaeomagnetic data would then have to be re-interpreted, as the sedimentary minerals could have aligned pointing to a "west pole" rather than the [[north magnetic pole]]. Alternatively, Earth's dipolar field could have been oriented such that the poles were close to the equator. This hypothesis has been posited to explain the extraordinarily rapid motion of the magnetic poles implied by the Ediacaran palaeomagnetic record; the alleged motion of the north magnetic pole would occur around the same time as the [[Gaskiers glaciation]].<ref>{{Cite journal| doi = 10.1016/j.epsl.2010.02.038| title = Incompatible Ediacaran paleomagnetic directions suggest an equatorial geomagnetic dipole hypothesis| year = 2010| last1 = Abrajevitch | first1 = A.| last2 = Van Der Voo | first2 = R.| journal = Earth and Planetary Science Letters| volume = 293| issue = 1–2| pages = 164–170| bibcode=2010E&PSL.293..164A}}</ref>

Another weakness of reliance on palaeomagnetic data is the difficulty in determining whether the magnetic signal recorded is original, or whether it has been reset by later activity. For example, a mountain-building [[orogeny]] releases hot water as a by-product of [[Metamorphism|metamorphic]] reactions; this water can circulate to rocks thousands of kilometers away and reset their magnetic signature. This makes the authenticity of rocks older than a few million years difficult to determine without painstaking mineralogical observations.<ref name=Meert1994pm>{{cite journal
| author = Meert, J.G.
| author2 = Van Der Voo, R.
| author3 = Payne, T.W.
| year = 1994
| title = Paleomagnetism of the Catoctin volcanic province: A new Vendian-Cambrian apparent polar wander path for North America
| journal = Journal of Geophysical Research
| volume = 99
| issue = B3
| pages = 4625–41
| doi = 10.1029/93JB01723
| bibcode=1994JGR....99.4625M
}}</ref> Moreover, further evidence is accumulating that large-scale remagnetization events have taken place which may necessitate revision of the estimated positions of the palaeomagnetic poles.<ref name=Font2010pm>{{cite journal
| author = Font, E
| author2 = C.F. Ponte Neto
| author3 = M. Ernesto
| year = 2011
| title = Paleomagnetism and rock magnetism of the Neoproterozoic Itajaí Basin of the Rio de la Plata craton (Brazil): Cambrian to Cretaceous widespread remagnetizations of South America
| journal = Gondwana Research
| volume = 20
| issue = 4
| pages = 782–797
| doi = 10.1016/j.gr.2011.04.005
| bibcode = 2011GondR..20..782F
}}</ref><ref name=Rowan2010pm>{{cite journal
| author = Rowan, C. J.
| author2 = Tait, J.
| year = 2010
| title = Oman's low latitude "Snowball Earth" pole revisited: Late Cretaceous remagnetisation of Late Neoproterozoic carbonates in Northern Oman
| journal = American Geophysical Union, Fall Meeting
| volume = 2010
| pages = GP33C–0959
| bibcode = 2010AGUFMGP33C0959R
}}</ref>

There is currently only one deposit, the Elatina deposit of Australia, that was indubitably deposited at low latitudes; its depositional date is well-constrained, and the signal is demonstrably original.<ref name=Sohl1999>{{cite journal
| author = Sohl, L.E. |author2=Christie-blick, N. |author3=Kent, D.V.
| year = 1999
| title = Paleomagnetic polarity reversals in Marinoan (ca. 600 Ma) glacial deposits of Australia; implications for the duration of low-latitude glaciation in Neoproterozoic time
| journal = Bulletin of the Geological Society of America
| volume = 111
| issue = 8
| pages = 1120–39
| doi = 10.1130/0016-7606(1999)111<1120:PPRIMC>2.3.CO;2
|bibcode = 1999GSAB..111.1120S | url = https://academiccommons.columbia.edu/doi/10.7916/D80P18JS/download
}}</ref>