News of the WeekPaleoclimatology

Snowball Earth Has Melted Back To a Profound Wintry Mix

Science  05 Mar 2010:
Vol. 327, Issue 5970, pp. 1186
DOI: 10.1126/science.327.5970.1186

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In 1998, a handful of geoscientists breathed new life into a daring idea: that Earth froze over from pole to pole more than a half-billion years ago, threatening life with extinction but perhaps prodding it to greater evolutionary heights. On page 1241 of this week's issue of Science, geoscientists report evidence that the tropics also hosted glaciers more than 100 million years before that supposed global freeze. Such low-latitude glaciation is a hallmark of so-called hard snowball Earth scenarios, in which a kilometer of ice sealed off the world ocean. But despite the new work, the much-studied hypothesis has fallen on hard times. Earth was profoundly cold in those geologically weird days, many agree—a "slushball" of a planet, perhaps. But sealed in ice? Unlikely.