Sterile soil continues metabolic activity for six years, challenging origins of life theories

Research led by Sébastien Fontaine at the French National Institute for Agriculture, Food, and Environment has demonstrated that sterilised soil continues to consume oxygen and emit carbon dioxide for at least six years. The study, published in Science Advances, suggests that abiotic geological processes, potentially catalysed by iron and aluminium oxides, can replicate metabolic reactions such as the Krebs cycle without living cells. These findings support theories that metabolism may have predated biological life on Earth.

For 15 years, Fontaine attempted to establish a baseline for carbon in lifeless soil to understand how much carbon is released by soil devoid of life. His team sealed soil in jars and sterilised it using gamma radiation, yet the soil continued to emit carbon dioxide. Initial results were published in the journal Biogeosciences in 2013, but the team faced skepticism regarding the sterility of the soil. Despite this, Fontaine persisted, ruling out experimental artifacts and confirming that the soil remained devoid of DNA or RNA even after extended irradiation.

The team detected a flow of electrons through the sterile soil using a fuel cell, with current levels several times higher than in a saltwater control, indicative of processes resembling the oxygen-dependent metabolism of the Krebs cycle. In a 2025 preprint on biorxiv.org, the authors reported observing four of the eight intermediate molecules known to be part of the Krebs cycle in six-month-old sterile soil samples. Many of these molecules formed after irradiation, suggesting that clods of earth can catalyse these reactions without the presence of life.

Glucose-augmented samples showed higher emission rates, strengthening the suspicion that nonbiological catalysts in soil can induce reactions that resemble the metabolic breakdown of sugar. This aligns with theories that metals such as iron and zinc, which sit at the core of ancient enzymes, might have catalysed reactions before life emerged. The findings imply that the chemistry of life is not exclusive to living organisms but is also a natural feature of geology.

While some experts suggest that residual enzymes from dead cells could account for the activity, Fontaine and his colleagues argue that enzyme stability diminishes exponentially and no enzyme is known to last six years. The study challenges previous assumptions about the necessity of life for such chemical activity, offering new insights into how biochemical cascades might have originated on the early Earth.