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Roughly 650 million years ago vast sheets of glaciers stretched from the poles to the tropics, entombing Earth within a frozen skin that lingered for millions of years. And this had happened before: Our “pale blue dot” has transformed into a pearly-white “snowball Earth” at least three times in our planet’s history. But these deep freezes present a conundrum: They should have been deadly and yet life clearly survived. There is both geologic evidence our earliest microscopic ancestors did not freeze to death and genetic indications the lineages of a range of single-celled organisms extend beyond snowball Earth. The question is how.

A new study published to the preprint server arXiv and submitted to Earth and Planetary Science Letters might provide a resolution. Adiv Paradise, an astronomy graduate student at the University of Toronto (U.T.), and his colleagues modeled a variety of possible snowball worlds—varying the numbers of volcanoes they host and the amount of stellar light they receive—only to find many of these worlds would never escape snowball status. Those that had little volcanic activity would never emit enough carbon dioxide to spark the runaway global warming needed to wake them from their cryogenic slumber (as likely happened on Earth). Yet surprisingly, many of these worlds could also support large unfrozen pockets of land. Some of those areas remain dry, like the McMurdo Dry Valleys in Antarctica, but others develop local hydrological cycles, allowing liquid water to pool and flow across their surfaces.

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Category: Science