The Living Subsurface: Microbial overprinting of subsurface geological processes and implications for natural resource exploration

Geochemical proxies are routinely interpreted as the outcome of abiotic fluid–rock interactions governed by pressure, temperature, and thermodynamic equilibrium. However, Earth’s subsurface hosts a vast and active biosphere up to several km depth that can alter the chemistry and isotopic composition of fluids and gases across a wide range of geological settings (Magnabosco et al. 2018; Giovannelli et al. 2022). Subsurface microorganisms are able to interact with volatiles such as H₂, CH₄, CO₂, and H₂S, and actively cycle key elements including C, S, N, Fe, and trace metals (Hay Mele et al. 2023), often inducing isotopic and compositional shifts that can overprint the signature of purely inorganic processes (Giovannelli et al. 2022; Barry et al. 2019). In this talk, I argue that subsurface microbiology represents a first-order control on many geochemical proxies used in resource exploration and management. I will review current knowledge on subsurface microbial communities and show how microbial metabolisms can reshape redox conditions, regulate gas accumulation and consumption, influence mineral precipitation and dissolution, and generate diagnostic, but frequently overlooked, geo(bio)chemical signatures. Using recent geomicrobiological data collected from diverse geological settings, I will demonstrate how biological activity can decouple classical geochemical tracers from their assumed abiotic origin. Finally, I will discuss emerging strategies to explicitly integrate microbiological processes into models and exploration workflows, to improve predictive frameworks and risk-assessment approaches for subsurface resources such as natural hydrogen, underground hydrogen storage, and carbon storage (Tyne et al., 2022; Cascone et al., 2025). Recognizing and quantifying the role of life in the subsurface is essential to correctly interpret geochemical data, reduce exploration uncertainty, and enable more robust and sustainable geological resource management.

 

Citations

Barry et al. 2019. Nature, 568: 487-492. 
Cascone et al. 2025. EarthArXiv, 8350: 1-35.
Giovannelli et al. 2022. Front, in Microbiol., 13: 998133.
Hay Mele et al. 2023. Essays in Biochem., 67: 1-18.
Magnabosco et al. 2018. Nature Geosci., 11: 707-717.
Tyne et al. 2023. Environ. Sci. Technol., 57(26): 9459-9473.