Water-rock reactions supporting the deep subsurface biosphere by producing electron donors and acceptors in the subsurface have been identified, from serpentinization (mineral hydration reactions), to radiogenic reactions. In the Stable Isotope Laboratory of Dr. Barbara Sherwood Lollar, this project focuses on the potential for a radiolytically driven H, S, and C deep cycle in the Earth’s subsurface, and the reaction mechanisms and rates sustaining deep subsurface microorganisms in the absence of interaction with the surface photosphere. The Earth-based focus on this work will have direct relevance for models of planetary habitability capable of sustaining subsurface chemolithotrophic life on planets or moons where photosynthesis may never have arisen. Field, laboratory and modelling opportunities are available to extend the existing program to explore the implications of our work on Earth analogs to the search for life on the rocky bodies and ocean worlds of our solar system.