For the entire history of our species, humans have lived on a planet capped by a chunk of ice at each pole. But Earth has been ice-free for about 75 percent of the time since complex life first appeared. This variation in background climate, between partly glaciated and ice-free, has puzzled geologists for decades.
Over the last 540 million years, as the Earth’s tectonic plates have shifted, researchers have found that periods of…
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