The answer depends on the region of the atmosphere and other factors, since the chemical composition of the Earth's atmosphere depends on temperature, altitude, and proximity to water. 1  Usually, the 4 most abundant gases are: 2  nitrogen (N2) - 78.084%. 3  oxygen (O2) - 20.9476%. 4  argon (Ar) - 0.934%. 5  carbon dioxide (CO2) 0.0314%.