Atmosphere of Earth development of animals. Today's atmosphere contains 21% oxygen, which is great enough for this rapid development of animals. "Air pollution" is the introduction into the atmosphere of chemicals, particulate matter or biological materials that cause harm or discomfort to organisms. Stratospheric ozone depletion is caused by air pollution, chiefly from chlorofluorocarbons and other ozone-depleting substances. The scientific consensus is that the anthropogenic greenhouse gases currently accumulating in the atmosphere are the main cause of global warming. On October 19, 2015 NASA started a website containing daily images of the full sunlit side of Earth on http://epic.gsfc.nasa.gov/. The images are taken
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