SUBSURFACE SULFUR SYSTEMS FOR ASTROBIOLOGICAL APPLICATIONS

Subsurface microbial systems dominated by sulfur chemistry are found in various parts of the world, including a handful of very unusual caves with extremely high levels of hydrogen sulfide gas. There are many more cave and other subsurface environments with lower concentrations of sulfur gases that receive significant energy from their underlying sulfur chemistry. We have suggested that similar systems could be present in subsurface environments, possibly in association with geothermal hot spots, on the sulfur rich planet Mars (Boston et al. 2001, 2005).

Our study in a sulfuric acid cave system in Mexico over the course of seven years has revealed a number of distinct microbial communities with identifiable macroscopic appearances, mineralogies, geochemical properties, and unique microbial community members (Hose et al. 2000; Boston et al 2005). Transformation from the living state to the lithified state is seen in several of these community types over very short spatial scales, providing unequivocal evidence that the lithified forms result from specific microbial biofilms and mats.

Several community types in the active modern Mexican cave strongly resemble ancient lithified remains from Lechuguilla Cave, NM, and other caves known to have been formed by sulfuric acid speleogenesis. Such identifiable biosignatures will be of great utility as templates in the search for traces of sulfur microbial systems on extraterrestrial life-detection missions.

We present suites of evidence from several of our well characterized sulfur microbial communities, including geochemical, isotopic, mineralogical, and biological lines of support.

Boston PJ, et al. Karst Geomorph. GSA Special Paper. In press. (2005).

Boston, PJ, et al. Astrobio. J. 1(1):25-55 (2001).

Hose, LD, et al. Chem. Geol. 169, 399-423 (2000).