Marine microbes drive biogeochemical interactions, bridging the link between biological systems and inorganic environments. Chemical or isotopic “biosignatures” left by these microbes allow us to investigate how biogeochemical cycles change in space and time. The physiology of marine microbes therefore integrates biogeochemical cycling with the biosignatures that are preserved in the geologic record. Sequencing advances in recent years have revolutionized our understanding of marine microbial diversity and metabolic potential, identifying both the organisms and environments that matter most. My research investigates the physiology of these key organisms in precisely controlled, environmentally relevant conditions to understand (1) how spatial changes in microbial physiology shape modern biogeochemical cycling (2) how temporal changes in microbial physiology may have changed biogeochemical cycling through Earth history and (3) how the evolutionary trajectory of microbial physiology will influence the biogeochemical cycling in future oceans.