Terrestrial Atmosphere Surface pressure: 1014 mb Surface density: 1.217 kg/m3 Scale height: 8.5 km Total mass of atmosphere: 5.1 x 1018 kg Total mass of hydrosphere: 1.4 x 1021 kg Average temperature: 288 K (15 C) Diurnal temperature range: 283 K to 293 K (10 to 20 C) Wind speeds: 0 to 100 m/s Mean molecular weight: 28.97 g/mole Atmospheric composition (by volume, dry air): Major : 78.084% Nitrogen (N2), 20.946% Oxygen (O2), Minor (ppm): Argon (Ar) - 9340; Carbon Dioxide (CO2) - 380 Neon (Ne) - 18.18; Helium (He) - 5.24; CH4 - 1.7 Krypton (Kr) - 1.14; Hydrogen (H2) - 0.55 Water is highly variable, typically makes up about 1% http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html