Hydrocarbons play key roles in atmospheric and biogeochemistry, the energy economy, and climate change. Most hydrocarbons form in anaerobic environments through high temperature or microbial decomposition of organic matter. Microorganisms can also “eat” hydrocarbons underground, preventing them from reaching the atmosphere. Using a new technique developed at the Earth-Life Science Institute (ELSI), an international team led by the Tokyo Institute of Technology professors Alexis Gilbert, Naohiro Yoshida and Yuichiro Ueno show that biological hydrocarbon degradation gives a unique biological signature. These findings could help detect subsurface biology and understand the carbon cycle and its impact on climate.