The origins of methane, a key biogeochemical component below the seafloor, can be elusive to determine. During my time as a C-DEBI postdoctoral fellow, I used new geochemical tools – the “clumped” isotopes of methane, to track how methane is being created and destroyed by microbial, thermogenic and abiotic processes in the deep biosphere. I cultured methanogens in the lab and showed that methylotrophs and hydrogenotrophs create methane with unique and distinguishable clumped isotope compositions, and that these compositions are insensitive to the rate of methanogenesis, temperature and species. I sailed on two International Ocean Discovery Program Expeditions to the Ross Sea (IODP 374) and the Guaymas Basin (IODP 385). Methane and microbes from these two end-member sites – the cold, carbon-poor, ice-sheet proximal Ross Sea and the hot, organic rich, active tectonic zone of the Gulf of California will further our understanding of how this new proxy can be used to identify sources and sinks of methane in the subsurface.