Methane

Methane is a chemical compound with the molecular formula CH4. It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning one molecule of methane in the presence of oxygen releases one molecule of CO2 (carbon dioxide) and two molecules of H2O:


 * CH4 + 2O2 → CO2 + 2H2O

Methane's relative abundance and clean burning process makes it a very attractive fuel. However, because it is a gas (at normal temperature and pressure; see STP), methane is difficult to transport from its source. In its natural gas form, it is generally transported in bulk by pipe or LNG carriers.

Methane is a relatively potent greenhouse gas with a high global warming potential of 72 (averaged over 20 years) or 25 (averaged over 100 years). Methane in the atmosphere is eventually oxidized, producing carbon dioxide and water. As a result, methane in the atmosphere has a half life of seven years (every seven years, the amount of methane halves).

The abundance of methane in the Earth's atmosphere in 1998 was 1745 parts per billion, up from 700 ppb in 1750. In the same time period, CO2 increased from 278 to 365 parts per million. The radiative forcing effect due to this increase in methane abundance is about one-third of that of the CO2 increase. In addition, there is a large, but unknown, amount of methane in methane clathrates in the ocean floors. Global warming could release this methane, which could cause a further sharp rise in global temperatures. Such releases of methane may have been a major factor in previous major extinction events. The Earth's crust also contains huge amounts of methane. Large amounts of methane are produced anaerobically by methanogenesis. Other sources include mud volcanoes which are connected with deep geological faults.

The only known species that uses methane instead of oxygen in respiration are the Grunts. The Grunts' home planet, Balaho has an atmosphere which is mostly methane. In all of the Halo games, they can be seen with breathing apparatus, because most of the battlefields they are stationed at do not have sufficient Methane. Methane is highly flammable, this may explain the fact that they sometimes explode in the halo novels.