Why Why Why the CO2 'Theory' Fails Earth's atmosphere, which is around 300 miles thick, is mainly made of nitrogen and oxygen, although there are many other trace substances in its composition. Trace substances make up only 1 percent of the bulk of the atmosphere while nitrogen (78 percent), oxygen (21 percent) and argon (1 percent) make up the rest. The minority 1 percent contains a variety of things, including minute amounts of neon, carbon dioxide, helium, krypton, methane, nitrous oxide, hydrogen, iodine, ozone, xenon, ammonia and carbon monoxide. At lower altitudes, water vapor may also be present. The atmosphere is divided into five layers, including the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The layer closest to Earth is the troposphere. It's around four to 12 miles thick. Scientists know the least about the mesosphere since weather balloons and jets can't reach its height (31 to 53 miles above the Earth) and satellites o...