Colorless, odorless gas with a wide distribution in nature. Chemical formula: CH4. It is the principal component of natural gas, a mixture containing about 75% CH4, 15% ethane (C2H6), and 5% other hydrocarbons, such as propane (C3H8) and butane (C4H10). The "firedamp" of coal mines is chiefly methane. anaerobic bacterial decomposition of plant and animal matter, such as occurs under water, produces marsh gas, which is also methane. At room temperature, methane is a gas less dense than air. It melts at -183°C and boils at -164°C. It is not very soluble in water. methane is combustible, and mixtures of about 5 to 15 percent in air are explosive. methane is not toxic when inhaled, but it can produce suffocation by reducing the concentration of oxygen inhaled.