Sohl and Chandler's models showed that changing one of the three main criteria (the paleogeography of the continents was not altered for the different models) was not enough to allow snow to accumulate on low latitude continents. Combining changes to solar luminosity and to atmospheric CO2 to 40 ppm (parts per million) would cause climate conditions needed for a "Snowball Earth", but there is no evidence to support such low numbers of CO2. Changes to all three criteria produced the same pattern seen when only luminosity and CO2 levels were changed.
Glacial Till
Researchers from University of St. Andrews, in Scotland, have collected other evidence that casts some doubt about the "Snowball Earth" theory. The researchers, led by Dr. Dan Condon, looked at tillite deposits in Scotland, Namibia, Ireland, and California. (Tillites are lithified deposits of glacial till that are produced by glaciers. Till is the unsorted rock and debris carried and eventually deposited by a glacial. It can be very fine grained and clay-sized on up to larger boulder-sized pieces.) Evidence of tillites suggests that there was a place for the large glaciers to deposit the rock and debris they carried with them. The Scottish researchers say the evidence recorded in the tillites demonstrates that there were open seas at the time of the "Snowball Earth".
Conclusion
All of the evidence presented by the detractors of the "Snowball Earth" theory eventually lead to the conclusion that part of the oceans were free of ice during the massive glaciation. This free ice region was important to sustain and promote life and allow it to expand after the glaciation events in the Late Precambrian and Cambrian periods. While the proponents of the "Snowball Earth" theory say life survived in isolated pockets across the globe and this was the reason for the explosion of life, the opponents of the theory conclude that such extreme climatic conditions would have devastated life on Earth. For the explosion of life we see after the glaciations there had to be large areas of open ocean for the life to survive and thrive during the glaciation.
Opponents of the "Snowball Earth" theory have not disputed the presence of continental glaciation in the low latitude continents. Climatic models even provide evidence that conditions could have existed to allow such tropical glaciers. However, the opponents do debate that the glaciers covered the oceans, instead arguing for un-glaciated tropical oceans in a theory that has been dubbed "Slushball Earth". Both sides of the debate have collected and present compelling evidence for their theories, and the debate between "Snowball" and "Slushball" is likely to continue until new light can be shed to swing the debate to one side or the other.
