Frozen Earth NPR's Richard Harris reports on a newly discovered climate calamity on Earth. Scientists report evidence that the earth plunged into a series of deep freezes so severe that even the oceans were covered with ice. These freezes were in turn punctuated by a series of heat spells. All this happened between 550 and 750 million years ago. Scientists now wonder whether those climate extremes helped trigger the evolution of advanced plants and animals on Earth.