Co-evolution of life and the environment on early Earth; study of the microfossil record associated with major climatic and geochemical oscillations in the Neoproterozoic.
Interplay among atmosphere, rock, water and microbes; the photochemical sulfur isotope effect, early microbial evolution, deep biosphere, and seafloor hydrothermal deposits.
Dynamical organization of the natural environment through investigation of the cooperative phenomena underlying common yet poorly understood observations. Work combines theory, field observations, and experiments to study problems including the carbon cycle and climate, the co-evolution of life and the environment, and the dynamics of fluids, rocks, and sand.
Biogeochemistry and geobiology: lipid chemistry of geologically significant microbes and microbial ecosystems; organic and isotopic indicators of climate change; evolution and mass extinction; biomarkers in sediments and petroleum; and biogeochemical fossils.