Life may have survived far north of equator during ‘Snowball Earth’

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https://www.science.org/content/article/life-may-have-survived-far-north-equator-during-snowball-earth

By Adam Mann, Science. 

Excerpt: More than 600 million years ago, the planet was frozen from pole to pole, covered in half-kilometer-thick ice sheets that darkened every ocean. How sea life clung on during Snowball Earth, as this inhospitable period is known, has long been a mystery. A new study bolsters the idea that the global glaciation wasn’t all encompassing. Geochemical evidence from ancient rocks suggests zones of open ocean may have been present north of the Tropic of Cancer, a region that was previously considered too cold to host life during this period. “There’s a habitable zone,” says Shuhai Xiao, a geobiologist at the Virginia Polytechnic Institute and State Universityand co-author of the new work. And it’s “perhaps wider than previously thought.” ...Climate models since the 1960s have shown how planetary deep freezes can arise from a simple feedback loop. When temperatures drop, Earth’s ice caps expand, reflecting sunlight and creating further cooling. If the ice manages to creep to roughly 30° to 40° latitude—about where North Africa and the continental United States are today—the global climate enters a runaway freezing cycle and glaciers end up covering the entire planet within a few hundred years. The geological record indicates Earth has experienced at least two such periods. The most recent one is known as the Marinoan Ice Age, between 654 million and 635 million years ago. Life was limited to the oceans and large creatures had yet to evolve, but fossils show that microscopic eukaryotes such as algae lived before and after the episode....

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