https://en.wikipedia.org/wiki/Snowball_Earth
https://blog.udn.com/edd/108761269
雪球地球是為了解釋一些地質現象而提出的假說。該假說認為在新元古代時候曾經發生過一次嚴重的冰河期，以至於地球上的海洋全部被凍結，僅僅在厚達兩公里的冰層下存有少量因地熱而融化的液態水。
加州理工學院地質教授約瑟夫·柯世韋因克於1992年首度使用「雪球地球」這個詞[2]。從那以後該假說得到了哈佛大學地質教授保羅·菲利克斯·霍夫曼及其同事丹尼爾·施拉格的大力支持和完善[3][4][5]。
The Snowball Earth is a geohistorical hypothesis that proposes during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen with no liquid oceanic or surface water exposed to the atmosphere. The most academically referred period of such global glaciation is believed to have occurred sometime before 650 mya during the Cryogenian period.
Proponents of the hypothesis argue that it best explains sedimentary deposits that are generally believed to be of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean,[3][4] and they emphasize the difficulty of escaping an all-frozen condition. Several unanswered questions remain, including whether Earth was a full snowball or a "slushball" with a thin equatorial band of open (or seasonally open) water. The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity.
