To do so we must know what energetic systems to look for. Astrobiology considers microorganisms that can utilize chemical energy sources, and especially anaerobic microorganisms. These include both mesophiles and thermophiles. Many of these metabolic types are subjects of study by UW microbiologists. We assume that life also requires carbon, nitrogen and energy sources, along with electron donors and acceptors.
Basaltic rock reacting with geothermally heated water can form chemicals that can support life.
On Mars there may still be both subsurface hydrothermal activity and water, and thus perhaps sources of chemical energy and electron acceptors and donors. Some models indicate that hydrothermal systems can produce organic compounds abiotically. Similarly, it has been hypothesized that CO2 can be reduced on pyrite surfaces, then condensed to form organic compounds, and that this reaction may have been associated with the metabolism of ancient microorganisms. Also, elemental and other forms of sulfur could be an energy source for subsurface microbes. As mentioned above, Leigh's lab is interested in the possibility that sulfur reduction was an ancient form of energy generation on Earth.