<P> Methane is created near the Earth's surface, primarily by microorganisms by the process of methanogenesis . It is carried into the stratosphere by rising air in the tropics . Uncontrolled build - up of methane in the atmosphere is naturally checked--although human influence can upset this natural regulation--by methane's reaction with hydroxyl radicals formed from singlet oxygen atoms and with water vapor . It has a net lifetime of about 10 years, and is primarily removed by conversion to carbon dioxide and water . </P> <P> In addition, there is a large (but unknown) amount of methane in methane clathrates in the ocean floors as well as the Earth's crust . </P> <P> In 2010, methane levels in the Arctic were measured at 1850 nmol / mol, a level over twice as high as at any time in the 400,000 years prior to the industrial revolution . Historically, methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol / mol during glacial periods commonly known as ice ages, and between 600 and 700 nmol / mol during the warm interglacial periods . Recent research suggests that the Earth's oceans are a potentially important new source of Arctic methane . </P> <P> Methane is an important greenhouse gas with a global warming potential of 34 compared to CO over a 100 - year period, and 72 over a 20 - year period . </P>

Density of ozone relative to methane under the same temperature and pressure condition is