Snowball Earth

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Snowball Earth refers to the hypothesis that the Earth's surface became nearly or entirely frozen at least once, sometime earlier than 650 million years ago. The geological community generally accepts this hypothesis because it best explains sedimentary deposits generally regarded as of glacial origin at tropical paleolatitudes and other otherwise enigmatic features in the geological record. Opponents to the hypothesis contested the implications of the geological evidence for global glaciation, the geophysical feasibility of an ice- or slush-covered ocean,[2][3] and the difficulty of escaping an all-frozen condition. There are a number of unanswered questions, including whether the Earth was a full snowball, or a "slushball" with a thin equatorial band of open (or seasonally open) water.

The geological time frames under consideration come before the sudden multiplication of life forms on earth known as the Cambrian explosion and the most recent snowball episode may have triggered the evolution of multi-cellular life on earth. Another, much earlier and longer, snowball episode, the Huronian glaciation (2.4 to 2.1 billion years) may have been triggered by the oxygen catastrophe.

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