Researchers have identified the mechanism by which bacteria create methane, a potent greenhouse gas. Methane-producing microbes are currently the most significant source of methane in the world, pumping hundreds of millions of metric tons into the atmosphere each year. Scientists have long sought to pinpoint the mechanism of the enzyme behind this synthesis, methyl-coenzyme M reductase (MCR), which has important implications for developing technologies to generate and harness methane for energy purposes. Two mechanisms that facilitate the reaction have been proposed: either a nickel atom, or a free radical. Determining which one is correct has been difficult because of the very quick speed of the reaction, where the intermediate substances are processed too quickly to analyze. As well, the state of the nickel atom during the reaction is highly sensitive to oxygen. Here, Thanyaporn Wongnate and colleagues chemically slowed down the reaction and used freezing techniques to analyze the reaction, ultimately determining that a free radical is the key mechanism in methane production. In a related Perspective, Thomas Lawton and Amy Rosenzweig convey the importance of this find, saying that, "Identification of the intermediate ends more than two decades of controversy and sets the stage for building a consensus MCR mechanism."