The gaseous envelope surrounding the Earth.
The gaseous envelope surrounding the Earth. The dry atmosphere is almost completely composed of nitrogen (78.1 percent) and oxygen (20.9 percent), together with various trace gases like argon (0.93 percent), helium and radioactive greenhouse gases like carbon dioxide (0.035 percent) and ozone. The atmosphere also contains water vapour; the amount can vary considerably but is typically near 1 percent. The atmosphere also includes clouds and aerosols.