Food additives such as 3-nitro·oxy·propanol can reduce the production of this compound in one organism, which can also be reduced using red algae. Berkeley Lab’s SUMMATION project monitors the dynamics of super-producers of this compound in the San Joaquin Valley. Nickel from Permian volcanism enabled the production of this compound by a genus partly named “sarcina,” which likely exacerbated the Great Dying. (-5[2])The Mcr (-5[1])complex evolves this compound from (*) acetate or hydrogen in archaea, which mainly generate sulfur or this compound at “white smokers.” Because their environments are oxygen-poor, microbes in rice paddies and wetlands are large producers of this substance, which is also produced by ruminant microbes in livestock. For 10 points, (10[1])the second-most potent greenhouse gas is what simplest alkane? (10[1])■END■ (10[2])