Geobiology of extreme environments including the deep subsurface, hydrothermal systems, ultrabasic/acidic systems, and caves; Compound‐specific isotope organic geochemistry (H,C,S) applied to microbial ecology, biogeochemical cycling in microbe‐rich environments and the sedimentary record of environmental perturbation; Neoproterozoic chemical evolution of the ocean‐atmosphere system during extreme isotope excursions; Carbonate sedimentology, stratigraphy, and geochemistry with an emphasis on microbialite preservation and morphology.