Credit: MTU 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. A new model, described in a study published in the Proceedings of the National Academy of Sciences , offers an explanation for these inconsistencies. Instead of consistent periods of ice, the new model suggests that cycles of glaciation and warm periods make more sense during the Sturtian period. Issues with 'Snowball' and 'Slushball' Earth models The dramatic swings in global temperature that cause periods of glaciation are linked to carbon and oxygen cycles.…