Popsicle PlanetThe atmospheric concentration of this heat-trapping greenhouse gas dropped so low in the Neoproterozoic that the planet froze over completely for 10 million years, killing off most life, which at the time consisted primarily of microbes and algae. In a dramatic reversal of fortunes, carbon dioxide then grew so abundant in the atmosphere that the ice thawed and Earth roasted, according to the hypothesis. The planet swung between icehouse and greenhouse at least four times, severely stressing the established organisms. Ultimately, this crisis may have triggered the evolution of the first recognizable animals. Seen from space during the Neoproterozoic glacial periods, Earth would have looked like a well-packed snowball, according to the new hypothesis. No patches of blue ocean. No clouds in the sky. Just ice, with perhaps some bare rock. The Snowball Earth hypothesis comes at an opportune time, when many scientists are starting to focus attention on the Precambrian time, especially its turbulent ending.
by Richard Monastersky
August 22, 1998
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