Our group uses the distribution and stable isotopic composition of biologically-produced organic molecules that accumulate in the environment to study climatic and ecological changes in the recent geologic past, and to determine how human activities influence these systems today. We make particular use of compound-specific hydrogen isotope ratios of lipid biomarkers. The large natural variability in these lipid hydrogen isotope ratios facilitates their use as proxies for diverse processes, and they encode information about climate, ecology, and metabolism. We work to improve our mechanistic understanding of the controls on the stable isotope distribution of biomarkers and other organic geological proxies, and apply these tools to answer questions about past changes and modern carbon cycling.