2018-06-07. Ancient Earth froze over in a geologic instant.

posted Jun 10, 2018, 3:22 AM by Alan Gould
By Lucas Joel, Science Magazine. For GSS Life and Climate chapter 8. Excerpt: Earth’s ice is melting at a rapid clip today. But some scientists think that during several ancient episodes, the planet plunged into a deep freeze known as “Snowball Earth,” when ice sheets grew to cover almost the entire planet. However, the number of these episodes, their extent, and just how fast Earth turned into an ice cube have long been a mystery. Now, analysis of a newly discovered rock sequence in Ethiopia supports a Snowball Earth event some 717 million years ago and suggests it took place in mere thousands of years—the geologic equivalent of a cold snap. The new work, grounded in Earth’s rock record, means the Snowball Earth hypothesis is “hanging in there, big time,” says Carol Dehler, a geologist at Utah State University in Logan, who was not involved in the research. ...Maclennan and colleagues ventured to the small town of Samre, Ethiopia, where they came across a type of rock—which they later dated to roughly 717 million years old—that could have only formed through glacial activity. These rocks, called diamictites, are made of huge boulders transported great distances by glaciers. Buried just below those glacial rocks were older layers of carbonate rocks. As the ancient supercontinent Rodinia was breaking apart, these rocks formed in shallow waters with the aid of microbial marine organisms—a sign that the same location was warm just a bit earlier in time, Maclennan explains. Together, these layers suggest the ancient climate quickly shifted from tropical paradise to frozen wasteland, Maclennan and colleagues report this month in Geology.... http://www.sciencemag.org/news/2018/06/ancient-earth-froze-over-geologic-instant