That the planet was covered by glacial ice for long periods during the Neoproterozoic is now an acceptable but still debated hypothesis, and there is some paper against the Snowball Earth. According to Allen (2008) there is evidence indicating that some oceans are ice-free and therefore contradicts the fact that the entire planet was covered by glacial ice. Snowball Earth may be according to Hoffman (1998) a reason for a collapse of biological productivity at the ocean surface. . Hoffman (1998) presents evidence that supports this rationale for global glaciation. Allen (2008) agrees with this to some extent. In Allen's report (2008) he accepts that there were cold periods and that the ice occupied tropical latitudes. But he contradicts a completely frozen land and points to deposited sedimentary rock. He argues that the rocks indicate some ice-free oceans and that sediments were transported out by glaciers. Both Allen (2008) and Hoffman (1998) then thought that the glaciation ended quickly due to very high levels of carbon dioxide. According to Hoffman (1998) carbon dioxide levels increased due to the release ...