Snowball Earth hypothesis, in geology and climatology, an explanation first proposed by American geobiologist J.L. Kirschvink suggesting that Earth’s oceans and land surfaces were covered by ice from the poles to the Equator during at least two extreme cooling events between 2.4 billion and 580 million years ago.
The evidence for this hypothesis is found in old rocks that preserved signs of Earth’s ancient magnetic field. Measurements of these rocks indicate that rocks known to be associated with the presence of ice were formed near the Equator. In addition, there is a 45-metre- (147.6-foot-) thick layer of manganese ore in the Kalahari Desert with an age corresponding to the end of the 2.4 billion-year “Snowball Earth” period; its deposition is thought to have been caused by rapid and massive changes in global climate as the worldwide covering of ice melted.
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