Anaerobic methanotrophs are a group of microbes that consume methane and live a low-energy lifestyle in oxygen-free environments. A new study shows that measuring the ratio of rare isotopes of methane from marine sediments is a useful tool for tracking their activities, which previously have been hard to distinguish from those of microbes that make methane. Featuring our most recent Network Speaker Series speaker, Jeanine Ash (watch the seminar on “Making and breaking Molecules,” now on YouTube).