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How Earth Might Have Turned Into a Snowball

Around 717 million years ago, Earth’s humid landscapes and roiling blue waters transformed into a frigid, barren world. Scientists nicknamed this stage of geological history, and others like it, Snowball Earth.

What exactly froze the planet nearly solid has been a mystery, as has how it remained that way for 56 million years. On Wednesday, a team of researchers at the University of Sydney said they have it figured out. Earth’s glaciation, they say, may have come from a global drop in carbon dioxide emissions, a result of fewer volcanoes expelling the gas into the atmosphere.

Less carbon dioxide makes it more difficult for Earth’s atmosphere to trap heat. If the depletion were extreme enough, they argued, it could have thrust the planet into its longest ice age yet.

The theory, published in the journal Geology, adds insight to the way geological processes influenced Earth’s past climate. It may also help scientists better understand trends in our current climate.

“These days, of course, humans are having a large impact on CO2 in the atmosphere,” said Adriana Dutkiewicz, a sedimentologist at the University of Sydney who led the study. “But back in time, there were no humans, and so everything was basically modulated by geological processes.”

There are many ideas about what turned Earth into a snowball. One popular theory suggests that minerals released by the weathering of igneous rock sucked enough carbon dioxide from the atmosphere to set off a deep freeze.

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