Earth ozone layer due to the subsequent conversion of atmospheric into. The ozone layer blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface
Atmospheric carbon cycle More than 70% of atmospheric methane comes from biogenic sources. Methane levels have risen gradually since the onset of the industrial era, from ~700 ppb in 1750 to ~1775 ppb in 2005. Methane can be removed from the atmosphere through a reaction of the photochemically produced hydroxyl free radical (OH). It can also leave the atmosphere by entering the stratosphere, where it is destroyed, or by being absorbed into soil sinks. Because methane reacts fairly quickly with other compounds, it does not stay in the atmosphere as long as many other greenhouse gases, e.g. carbon dioxide. It has an atmospheric