Figure 21.25Ancient glaciations. (a) The first map shows the extent of the Permian-Carboniferous glaciation, which occurred more than 300 million years ago. At that time, the southern continents were assembled into the giant continent Gondwana, and the ice cap was situated in the Southern Hemisphere, centered over Antarctica, which is home to a continental glacier today. The second map shows the distribution of Permian-Carboniferous glacial deposits today. (b) Permian glacial deposits from South Africa. (c) Late Proterozoic glacial deposits. (d) The development of a late Proterozoic Snowball Earth. Geologists debate the extent to which ice covered the globe, but some think even the oceans became frozen.