http://www.sciencemag.org/news/2019/04/ancient-snowball-earth-thawed-out-flash

An artist’s impression of what Earth looked like during the Snowball Earth glaciations.

More than half a billion years ago, our planet was a giant snowball hurtling through space. Glaciers blanketed the globe all the way to the equator in one of the mysterious “Snowball Earth” events geologists think occurred at least twice in Earth’s ancient past. Now, scientists have found that the final snowball episode likely ended in a flash about 635 million years ago—a geologically fast event that may have implications for today’s human-driven global warming.