Metabolic activity imparts diagnostic stable isotopic signatures into biomass and geochemical phases in the environment. In my research, I use the stable isotopic signatures of carbon and sulfur species to reconstruct the presence and activity of specific metabolic pathways and processes in natural environments. Specifically, these measurements are used to probe (micro)-biological activity and its dependence on the ambient geochemical environment to address: 1) what controls the rates and types of metabolic activity; 2) how this activity impacts the ambient geochemical environment; 3) how the resulting chemical signatures get preserved over geologic time; and 4) how to extract information from ancient sediments to best reconstruct paleoenvironmental conditions. My approach involves combining diverse measurements collected across a range of spatial and temporal scales to maximize our understanding of organism-environment interactions in natural systems.