Methane is a potent greenhouse gas, second only to carbon dioxide in its capacity to trap heat in Earth’s atmosphere for a long time. The gas can originate from lakes and swamps, natural-gas pipelines, deep-sea vents, and livestock. Understanding the sources of methane, and how the gas is formed, could give scientists a better understanding of its role in warming the planet.

Individual cows can produce up to 500 liters of methane a day; the species accounts for about one-third of total methane emissions. The structures shown represent the structure of methane.