For 15 years, Sébastien Fontaine has been trying to kill dirt. The biochemist, who runs a lab at the French National Institute for Agriculture, Food, and Environment, wanted to know how much carbon is released by soil — just dirt alone, completely devoid of life. His team sealed dirt into jars and blasted them with sterilizing gamma radiation. Then they waited for the carbon dioxide released by the soil — a sign of ongoing microbial respiration — to drop. They waited, and waited, and waited some more: weeks, then months. Under a microscope, the irradiated soil showed no signs of life, but it continued to emit carbon dioxide. The soil wouldn’t stop breathing. Fontaine’s lab repeated the experiments and produced the same results. Finally, convinced that they weren’t dealing with an artifact of the experimental setup, they set out to find the source of breath in dead soil.…