The most abundant gas in the Earth's atmosphere is nitrogen. Nitrogen makes up 78 percent of the Earth's atmosphere, and it is a permanent gas, which means that its percentage does not change on a daily basis. The rest of the atmosphere is made up of 21 percent oxygen, 0.9 percent argon and 0.1 percent trace gases.
Trace gases such as ozone, methane, helium, nitrous oxide, neon and carbon dioxide account for about one-tenth of the Earth's atmosphere. Their concentrations are always changing and differ in one region to the next, and they are also found in different concentrations depending on the time of day. Earth's atmosphere is most concentrated on the surface and quickly thins as elevations increase, eventually merging with space about 100 miles above sea level.