In Siberian permafrost, in the Arctic, in Chile’s nearly rainless Atacama Desert, and in the dark forests of Poland, organisms have been found that appear lifeless yet will revive and become fully functional when propitious environmental conditions arise. The question these discoveries evoke is not merely how life endures in harsh, inhospitable-to-life places, but what, exactly, it retains while doing so. Consider the bdelloid rotifer, a microscopic animal invisible to the naked eye and seemingly indifferent to the usual limits of survival. In a laboratory in Pushchino, Russia, researchers revived rotifers that had been frozen in Siberian permafrost for more than 24,000 years. During that interval, the animals existed in cryptobiosis, a reversible state of suspended animation. “This is the hardest proof so far,” Stas Malavin, one of the researchers, remarked, “that multicellular animals can withstand tens of thousands of years in a state of almost completely arrested metabolism.” Cryptobiosis is not death, though it resembles it closely enough to make the distinction difficult. Growth stops. Repair ceases. There is no signaling, no transcription, and …