Methane (CH4) is a colorless, odorless, flammable, greenhouse gas. It is released naturally into the air from marshes, swamps, rice fields, ruminant animals (such as cattle), and sewage sludge. CH4 is also released from methane-producing bacteria (methanogens) that live in anaerobic places. [Solar Energy; v52n6; 467-477; 1994.] [Air, The Nature of Atmosphere and the Climate; Michael Allaby; pages 39,40; 1992; Facts on File; New York] [Dictionary of Science; R.K. Barnhart; page 398; 1986; Houghton Mifflin Company; Boston.]