|
| issue = 5
}}</ref> (model yang berikutnya menunjukkan bahwa es itu bahkan mendekat sampai 25° atau kurang dari kathulistiwa tanpa memulai glasiasi total<ref name=Meert1994pm/>). Jadi, kehadiran deposit glasial dekat dengan wilayah tropis tampaknya menunjuk kepada penutupan es global.
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Critical to an assessment of the validity of the theory, therefore, is an understanding of the reliability and significance of the evidence that led to the belief that ice ever reached the tropics. This evidence must prove two things:
# that a bed contains sedimentary structures that could have been created only by glacial activity;
# that the bed lay within the tropics when it was deposited.
During a period of global glaciation, it must also be demonstrated that glaciers were active at different global locations at the same time, and that no other deposits of the same age are in existence.
This last point is very difficult to prove. Before the [[Ediacaran]], the biostratigraphic markers usually used to correlate rocks are absent; therefore there is no way to prove that rocks in different places across the globe were deposited at the same time. The best that can be done is to estimate the age of the rocks using radiometric methods, which are rarely accurate to better than a million years or so.<ref name=Eyles2004/>
The first two points are often the source of contention on a case-to-case basis. Many glacial features can also be created by non-glacial means, and estimating the latitude of landmasses even as little as {{Ma|200}} can be riddled with difficulties.<ref name=Briden1971>{{cite journal
| author = Briden, J.C.
| coauthors = Smith, A.G.; Sallomy, J.T.
| year = 1971
| title = The geomagnetic field in Permo-Triassic time
| journal = Geophys. JR astr. Soc.
| volume = 23
| pages = 101–117
| doi = 10.1111/j.1365-246X.1971.tb01805.x
}}</ref>
-->
=== Palaeomagnetisme ===
Mengingat plat tektonik bergerak setiap saat, penentuan posisinya pada suatu waktu dalam sejarah tidaklah mudah. Selain pertimbangan bagaimana daratan dapat cocok merapat, latitude deposit batu-batuan dapat dibatasi oleh palaeomagnetisme. Ketika batuan sedimentari terbentuk, mineral bermagnet di dalamnya cenderung menyesuaikan diri dengan medan magnet bumi. Melalui pengukuran cermat [[palaeomagnetisme]], dimungkinkan untuk memperkirakan [[latitude]] (tapi [[longitude]] tidak) di mana matriks batuan itu didepositkan. Pengukuran paleomagnet mengindikasikan bahwa sejumlah sedimen glasial pada catatan batuan era [[Neoproterozoic]] didepositkan di dalam jangkauan 10 derajat dari kathulistiwa,<ref name="Evans">{{cite journal
| 