|
| url = http://geology.geoscienceworld.org/cgi/content/abstract/23/2/153
| accessdate =27 April 2007
|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 doi
| 10.1016/0012-821X(94)90253-4}}</ref>
Skeptics suggest that the palaeomagnetic data could be corrupted if the Earth's magnetic field was substantially different from today's. Depending on the rate of cooling of the Earth's core, it is possible that during the Proterozoic, its [[magnetic field]] did not approximate a [[dipole|dipolar]] distribution, with a North and South pole 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. Paleomagnetic data would then have to be re-interpreted as particles could align pointing to a 'West Pole' rather than the North Pole. Alternatively, the Earth's dipolar field could have 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 pole would occur around the same time as the Gaskiers glaciation.<ref>{{cite doi
| 10.1016/j.epsl.2010.02.038}}</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 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.
| coauthors = Van Der Voo, R.; 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
| url = http://www.agu.org/pubs/crossref/1994.../93JB01723.shtml
| accessdate =11 March 2008
| doi = 10.1029/93JB01723
| bibcode=1994JGR....99.4625M
}}</ref> Moreover, further evidence is accumulating that large-scale remagnetization events have taken place, that may require revision of the position of the paleomagnetic poles.<ref
name=Font2010pm>{{cite journal
| author = Font, E
| coauthors = C.F. Ponte Neto, 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
| url = http://www.sciencedirect.com/science/article/pii/S1342937X11001250
| accessdate =6 May 2011
| doi = 10.1016/j.gr.2011.04.005
}}</ref><ref name=Rowan2010pm>{{cite journal
| author = Rowan, C. J.
| coauthors = Tait, J.
| year = 2010
| title = Oman's low latitude "Snowball Earth" pole revisited: Late Cretaceous remagnetisation of Late Neoproterozoic carbonates in Northern Oman| journal = The Smithsonian/NASA Astrophysics Data System
| volume = American Geophysical Union, Fall Meeting 2010
| issue = abstract #GP33C–0959
| bibcode = 2010AGUFMGP33C0959R
| last2 = Tait
| pages = 0959
}}</ref>
-->
Ada satu deposit, Elatina di Australia, yang jelas didepositkan pada latitude rendah; tarikhnya sungguh terbataas, dan signalnya benar-benar asli.<ref name=Sohl1999>{{cite journal
| author = Sohl, L.E.
| doi = 10.1046/j.1365-3091.2002.00466.x
| url =
}}</ref> <!--Thus the glacial origin of many of the key occurrences for snowball Earth has been contested.<ref name="Eyles2004" />
As of 2007, there was only one "very reliable" – still challenged<ref name="Eyles2004" /> – datum point identifying tropical [[tillite]]s,<ref name="Evans" /> which makes statements of equatorial ice cover somewhat presumptuous. However evidence of sea-level glaciation in the tropics during the [[Sturtian]] is accumulating.<ref name='Macdonald2010'>{{cite doi
| 10.1126/science.1183325
| laysummary=10.1126/science.327.5970.1186 }}</ref>
Evidence of possible glacial origin of sediment includes:
* [[Dropstones]] (stones dropped into marine sediments), which can be deposited by glaciers or other phenomena.<ref name=Donovan1997>{{cite journal
| author = Donovan, SK
| coauthors = Pickerill, RK
| date = 27 April 2007 1997
| title = Dropstones: their origin and significance: a comment
| journal = Palaeogeography, Palaeoclimatology, Palaeoecology
| volume = 131
| issue = 1
| pages = 175–8
| doi = 10.1016/S0031-0182(96)00150-2
}}</ref>
* [[Varves]] (annual sediment layers in periglacial lakes), which can form at higher temperatures.<ref name=Thunell1995>{{cite journal
| author = Thunell, R.C.
| coauthors = Tappa, E., Anderson, D.M.
| date = 1 December 1995
| title = Sediment fluxes and varve formation in Santa Barbara Basin, offshore California
| journal = Geology
| volume = 23
| issue = 12
| pages = 1083–6
| doi = 10.1130/0091-7613(1995)023<1083:SFAVFI>2.3.CO;2
| url = http://geology.geoscienceworld.org/cgi/content/abstract/23/12/1083
| accessdate =27 April 2007
|bibcode = 1995Geo....23.1083T }}</ref>
* [[Glacial striation]]s (formed by embedded rocks scraped against bedrock): similar striations are from time to time formed by [[mudflow]]s or tectonic movements.<ref name=Jensen1996>{{cite journal
| author = Jensen, PA
| coauthors = Wulff-pedersen, E.
| date = 1 March 1996
| title = Glacial or non-glacial origin for the Bigganjargga tillite, Finnmark, Northern Norway
| journal = Geological Magazine
| volume = 133
| issue = 2
| pages = 137–45
| url = http://geolmag.geoscienceworld.org/cgi/content/abstract/133/2/137
| accessdate =27 April 2007
| doi = 10.1017/S0016756800008657
}}</ref>
* [[Diamictite]]s (poorly sorted conglomerates). Originally described as glacial [[till]], most were in fact formed by [[debris flow]]s.<ref name=Eyles2004>{{cite journal
| author = Eyles, N.
| coauthors = Januszczak, N.
| year = 2004
| title = 'Zipper-rift': A tectonic model for Neoproterozoic glaciations during the breakup of Rodinia after 750 Ma
| journal = Earth-Science Reviews
| volume = 65
| issue = 1–2
| pages = 1–73
| doi = 10.1016/S0012-8252(03)00080-1
| url = http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V62-4B723V6-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=757070dcaa8d8b501170dfde579d792f
|format=PDF| accessdate =4 May 2007
| bibcode=2004ESRv...65....1E
}}</ref>
===Open-water deposits===
It appears that some deposits formed during the snowball period could only have been formed in the presence of an active hydrological cycle. Bands of glacial deposits up to 5,500 meters thick, separated by small (meters) bands of non-glacial sediments, demonstrate that glaciers were melting and re-forming repeatedly for tens of millions of years; solid oceans would not permit this scale of deposition.<ref name=Condon2002>{{cite journal
| author = Condon, D.J.
| coauthors = Prave, A.R., Benn, D.I.
| date = 1 January 2002
| title = Neoproterozoic glacial-rainout intervals: Observations and implications
| journal = Geology
| volume = 30
| issue = 1
| pages = 35–38
| doi = 10.1130/0091-7613(2002)030<0035:NGRIOA>2.0.CO;2
| url = http://geology.geoscienceworld.org/cgi/content/abstract/30/1/35
| accessdate =4 May 2007
|bibcode = 2002Geo....30...35C
}}</ref> It is considered possible that [[ice stream]]s such as seen in [[Antarctica]] today could be responsible for these sequences.
Further, sedimentary features that could only form in open water, for example [[wave-formed ripples]], far-traveled [[ice-rafted debris]] and indicators of photosynthetic activity, can be found throughout sediments dating from the snowball Earth periods. While these may represent 'oases' of [[meltwater]] on a completely frozen Earth,<ref name=Halverson2004>{{cite journal
| author = Halverson, G.P.
| coauthors = Maloof, A.C., Hoffman, P.F.
| year = 2004
| title = The Marinoan glaciation (Neoproterozoic) in northeast Svalbard
| journal = Basin Research
| volume = 16
| issue = 3
| pages = 297–324
| doi = 10.1111/j.1365-2117.2004.00234.x
| url = http://geoweb.princeton.edu/people/maloof/downloads/marinoan.pdf
| accessdate =5 May 2007
}}</ref> computer modelling suggests that large areas of the ocean must have remained ice free arguing that a "hard" snowball is not plausible in terms of energy balance and general circulation models.<ref name="Peltier">{{cite book
| last= Peltier
| first=W.R.
| authorlink=
| editor=Jenkins, G.S., McMenamin, M.A.S., McKey, C.P., & Sohl, L.
| title=The Extreme Proterozoic: Geology, Geochemistry, and Climate
| year=2004 |publisher=American Geophysical union |pages=107–124
| chapter=Climate dynamics in deep time: modeling the "snowball bifurcation" and assessing the plausibility of its occurrence}}</ref>
-->
=== Rasio isotop karbon ===
Ada dua isotop karbon stabil di air laut: [[karbon-12]] (<sup>12</sup>C) dan [[karbon-13]] (<sup>13</sup>C) yang jarang ada, keseluruhan membentuk 1.109 persen atom karbon. Proses biokimia, di antaranya [[fotosintesis]], cenderung memilih melibatkan isotop <sup>12</sup>C yang lebih ringan. Jadi pelaku fotosintesis di lautan, baik [[protista]] dan [[algae]], cenderung kekurangan <sup>13</sup>C, relatif terhadap yang banyak ditemukan di sumber vulkanik primer untuk karbon di bumi. Maka, suatu lautan dengan kehidupan fotosintesis akan mengandung rasio <sup>13</sup>C/<sup>12</sup>C yang lebih kecil dalam bekas-bekas organik, terutama dibandingkan dengan air laut. Komponen organik sedimen membatu (''lithified sediment'') akan selamanya sedikit, tetapi terukur, kekurangan <sup>13</sup>C.
| 