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Warm band may have girdled snowball Earth

In the era before multicelled animals appeared some 550 million years ago, extreme cold may have clutched Earth in a death grip for millions of years. According to the controversial snowball Earth theory, the planet swung between deep freeze and feverish heat several times during a 200-million-year period preceding the multicellular explosion.

Offering an alternative to the snowball theory's ice-engulfed planet, a team of researchers from Texas and Canada now demonstrates that a swath of liquid ocean may have hugged the planet's midriff even during the chilliest episodes.

"That life survived through this episode seems to favor this open-ocean solution," says William T. Hyde of Texas A&M University in College Station. He and his colleagues describe their computer simulations in the May 25 Nature.

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