<P> Research suggests that the implied methane destruction lifetime is as long as ~ 4 Earth years and as short as ~ 0.6 Earth years . This lifetime is short enough for the atmospheric circulation to yield the observed uneven distribution of methane across the planet . In either case, the destruction lifetime for methane is much shorter than the timescale (~ 350 years) estimated for photochemical (UV radiation) destruction . The rapid destruction (or "sink") of methane suggests that another process must dominate removal of atmospheric methane on Mars, and it must be more efficient than destruction by light by a factor of 100 to 600 . This unexplained fast destruction rate also suggests a very active replenishing source . In 2014 it was concluded that presence of strong methane sinks are not subject to atmospheric oxidation . A possibility is that the methane is not consumed at all, but rather condenses and evaporates seasonally from clathrates . Another possibility is that methane reacts with tumbling surface sand quartz (SiO) and olivine to form covalent Si--CH bonds . </P> <P> The principal candidates for the origin of Mars' methane include non-biological processes such as water--rock reactions, radiolysis of water, and pyrite formation, all of which produce H that could then generate methane and other hydrocarbons via Fischer--Tropsch synthesis with CO and CO . It has also been shown that methane could be produced by a process involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars . The required conditions for this reaction (i.e. high temperature and pressure) do not exist on the surface, but may exist within the crust . A detection of the mineral by - product serpentinite would suggest that this process is occurring . An analog on Earth suggests that low - temperature production and exhalation of methane from serpentinized rocks may be possible on Mars . Another possible geophysical source could be ancient methane trapped in clathrate hydrates that may be released occasionally . Under the assumption of a cold early Mars environment, a cryosphere could trap such methane as clathrates in stable form at depth, that might exhibit sporadic release . </P> <P> A group of Mexican scientists performed plasma experiments in a synthetic Mars atmosphere and found that bursts of methane can be produced when a discharge interacts with water ice . A potential source of the discharges can be the electrification of dust particles from sand storms and dust devils . The ice can be found in trenches or in the permafrost . The electrical discharge ionizes gaseous CO and water molecules and their byproducts recombine to produce methane . The results obtained show that pulsed electrical discharges over ice samples in a Martian atmosphere produce about 1.41 × 10 molecules of methane per joule of applied energy . </P> <P> Living microorganisms, such as methanogens, are another possible source, but no evidence for the presence of such organisms has been found on Mars . In Earth's oceans, biological methane production tends to be accompanied by ethane, whereas volcanic methane is accompanied by sulfur dioxide . Several studies of trace gases in the Martian atmosphere have found no evidence for sulfur dioxide in the Martian atmosphere, which makes volcanism unlikely to be the source of methane . </P>

What was the most abundant gas present in the original planetary atmosphere