Snowball Earth may hide a far stranger climate cycle than anyone expected

During the Sturtian glacial period during the Neoproterozoic Era, Earth underwent periods of global glaciation, which have been described as either "Snowball" and "Slushball" Earth scenarios. In Snowball Earth models, the planet was completely covered in ice for around 56 million years. In the Slushball models, portions of thin or patchy ice or even open water still existed in the tropics. However, there are some inconsistencies between these models and geological and biological evidence.