Coaling in the deep
Despite our current reliance on fossil carbon for energy, the biogeochemical reactions that produce coal and natural gas aren’t entirely understood. Lloyd
et al
. tested the chemistry and isotope composition in samples ranging from wood to hard, mature coal (see the Perspective by Keppler). Methyoxyl groups in this organic material, which are a potential source of methane, declined with maturity, whereas the carbon-13 fraction increased gradually. The most plausible explanation for this observed pattern is biological demethylation under substrate-limited conditions. These results help us understand the processes that form coal and natural gas on geologic time scales. —MAF