LIFE AS WE DON’T KNOW IT. “Underground water or other fluid sources, in combination with flux of secondary particles can provide a stable self-sustained environment for life to exist. Low energy availability can produce organisms with a very slow metabolism. There is a possibility of an ecosystem thriving on this energy source based on other biochemical bases, and might necessitate alternative approaches to detect life ‘as we don’t know it’ in subsurface environments on Earth and elsewhere.”
https://royalsocietypublishing.org/doi/10.1098/rsif.2016.0459