Changes in the Chemical Composition of the Atmosphere and Potential Impacts

The story of the importance of atmospheric chemistry begins with the origin and evolution of life on Earth. The accumulation of greenhouse gases in Earth’s atmosphere allowed surface temperatures to be maintained above the freezing point of water. Reactions involving carbon, hydrogen, and nitrogen compounds in the primeval soup led to the formation of self-replicating molecules, and, about 500 million years ago, the rise of atmospheric oxygen led to the formation of the stratospheric ozone layer, which protects life on Earth from extremely harmful levels of solar ultraviolet radiation. Running in the shadow of these major events has been a full suite of atmospheric chemistry processes affecting and being affected by the evolving nature of both terrestrial and oceanic life. Some of these processes include biogeochemical cycling of elements, long-range transport of nutrients, regulation of temperature, and exposure to air pollution.