Reality → Matter → Earth → Atmosphere
| Air | |
|---|---|
| nitrogen | 78% |
| oxygen | 21% |
| argon | 1% |
| carbon dioxide | 0.04% |
About 3/4 of the atmosphere’s mass is concentrated in a 11 km thick layer (at scale, this is less than the skin of an apple). With increasing height, the air gets ever thinner, without any defined border between atmosphere and space; for practical reasons, it is often assumed that the atmosphere stops and space begins at 100 km height above sea level [1] . Due to Earth’s gravity, the air cannot escape (diffuse) into space, it rather rests with a weight of 10 000 kilogram (10 tonnes) on each square meter of Earth’s surface. The total mass of the atmosphere is about 50 Tt (50 teratonnes, or 50 × 1012 t), but this hefty mass accounts only for a minuscule 0.000 001 % of Earth’s mass [2] . The atmosphere protects life from harmful cosmic rays and is impacted by the biosphere [3] .
More than 99.999% of the atmosphere’s mass is accumulated below an elevation of 100 km. The highest altitude a rocket-propelled airplane can reach is also about 100 km, due to the air’s diminished lifting capacity and the barrier of the escape velocity. Astronauts have reported that on re-entry of the space shuttle the first effects of the atmosphere become noticeable at about this altitude. Above that elevation, the air’s sparse molecules are ionized by solar radiation. Well above 100 km altitude, the beautiful auroras of the polar regions are caused by interaction of solar winds (plasma eruptions) and the Earth’s magnetic field .
Oceans also make only a tiny contribution (0.02%) to Earth's total mass. Even the crust contributes only 0.4%. More than 99% of mass come from mantle and core.