ABSTRACT
We live and breathe in the atmosphere, a sea of gas consisting primarily of elemental O2 and N2, with signifi cant amounts of water vapor, noble gas argon, carbon dioxide, and trace quantities of other gases. Unlike the ocean with its well-defi ned volume and surface, the atmosphere extends for many kilometers from Earth’s surface, becoming less dense with increasing altitude. With increasing altitude the air simply gets thinner and thinner, but there is not a distinct altitude at which the atmosphere ends and outer space begins.
