650 million years ago, the Earth’s water completely froze over-an event known as a snowball earth. Such extreme conditions should have wiped out life, but there is a clear continuity of microbes from before and after this event. How? Adiv Paradise, a graduate student from the University of Toronto, and his colleagues have an idea. Using a model with variable starlight and greenhouse gas output from volcanoes, they found that some snowball earths still have large pockets of dry, arid land, like the cold deserts of Antarctica, and can still have some regions where liquid water can flow, creating local hydrological cylces. This gives hope for observations of exoplanets, as snowball exoplanets may still be habitable.
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