Sterilized soil keeps 'breathing' for six years, hinting metabolism predates life

French biochemist Sébastien Fontaine spent 15 years trying to fully kill soil samples and explain why they wouldn’t stop emitting carbon dioxide. After blasting dirt with gamma radiation, heat, and pressure — and confirming via electron microscopy and RNA/DNA staining that no living cells remained — his team watched the sterile samples continue consuming oxygen and releasing CO2 for over 2,400 days. Adding glucose accelerated emissions; adding yeast enzymes spiked them, suggesting a reaction was already underway that enzymes merely catalyzed faster.

In a Science Advances paper and a 2025 bioRxiv preprint, Fontaine’s group reports detecting four of the eight intermediate molecules of the Krebs cycle in months-old sterile soil, and measured electron currents through irradiated dirt several times stronger than through a saltwater control. Their interpretation: iron and aluminum oxides naturally present in soil can catalyze the same energy-releasing reactions that cells perform with enzymes, meaning core metabolic chemistry isn’t exclusive to living systems.

The finding aligns with a metabolism-first school of origin-of-life research, which argues that mineral-catalyzed reactions resembling the Krebs cycle could have run on the early Earth before enzymes and genes evolved to control them. As one outside chemist put it, the chemistry of life may really be the chemistry of geology.