An Etymological Dictionary of Astronomy and Astrophysics

Any of several episodes in the history of the Earth where our planet was entirely covered by glacial ice from pole to pole. There are at least three such episodes.

The first one, called the Huronian glaciation, extended from 2.4 billion years ago to 2.1 billion years (lasting about 300 million years).
In the last billion years, the Earth has experienced two more global glaciations: the Sturtian glaciation, which began 720 million years ago and, following a brief interglacial episode, the Marinoan glaciation, which ended 635 million years ago. During such episodes the global mean temperature would be about -50°C because most of the Sun’s radiation would be reflected back to space by the icy surface. The average equatorial temperature would be about -20°C, roughly similar to present Antarctica. Without the moderating effect of the oceans, temperature fluctuations associated with the day-night and seasonal cycles would be greatly enhanced. Because of its solid surface, the climate on a snowball earth would have much in common with present Mars (http://www.snowballearth.org).

Etymology (EN): The term snowball Earth was coined in 1989 by Joe Kirschvink, a biomagnetist and paleomagnetist at the Caifornia Institute of Technology in Pasadena, USA; → earth.