Composition of the Atmosphere

Most of air is dinitrogen (N2). The second most abundant gas is oxygen (O2). After that comes the inert gas argon (Ar), and there are also many minor components at the less than 1% level. One of these is carbon dioxide (CO2) which performs such an important insulating task in its role as a greenhouse gas. Without the trace amounts of CO2 the planet would be (literally) freezing cold.