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.
Now, Fontaine and his colleagues have reported that their soil samples continued to consume oxygen and spew carbon dioxide for six years. In a 2025 paper in Science Advances, they proposed that a metabolic process that powers much of life is also possible outside living cells. Their experiments point to how it could work in dirt, absent the living proteins that would typically organize it. If they’re right, some biochemical reactions, such as those that release the energy of carbon-rich sugar molecules, may not be unique to living things. Such reactions — known as metabolism when performed by cells — could even predate life on Earth, Fontaine said.
The experiments show “what happens to biomolecules when they’re left to their own devices,” said Joseph Moran, an organic chemist at the University of Ottawa who was not involved with the research. They’re finding that the chemistry of life is not exclusive to life, he added. “It’s the chemistry of geology.”
[---]
For Joshua Schimel, a soil ecologist at the University of California, Santa Barbara, Fontaine’s findings were not too surprising. “Glucose naturally, in the process of being oxidized, is going to form some of these Krebs-cycle intermediates,” he said. Many soils are rich in iron oxides and aluminum oxides, which can catalyze this conversion, he added.
The idea that metals can catalyze biochemical reactions is central to a theory about the origins of life that has emerged over the last decade. Metals such as iron and zinc sit at the core of many of the most ancient enzymes found across life forms. Some researchers, including Moran, believe they might have catalyzed these reactions before life emerged. Studies, including his, suggest that the chemical reactions that break down and construct glucose derivatives, which are normally associated with life, might have existed before the enzymes and genes that enable them in living cells.
“There’s a handful of researchers like myself that think, actually, we should organize our thoughts about life in a different way — that we actually should put metabolism at the base of what life is doing, and then genes are a way of controlling that at a higher level,” Moran said.
Cell-free metabolic reactions could be more common than previously thought and don’t need special conditions to get started, said Markus Ralser, a biochemist at Charité University Hospital in Berlin, who found some of the first enzyme-free metabolic reactions.
“This fits a bit into my thinking about how metabolism started in evolution,” he said of the new work. “If it would be very hard to do, then the planet would not be full of life now.” This idea is complicated, however, by the low-oxygen conditions in which life arose.
- More Here
