The four main gases in the atmosphere are nitrogen, oxygen, argon and carbon dioxide. However, two of these gases make up most of the atmosphere. They are nitrogen and oxygen, which between them account for over 99 percent of the atmosphere.
Nitrogen is the most common gas. Over 78 percent of the atmosphere is made up of this gas. Nitrogen is essential to life on Earth, with most living things using it to make proteins. It also dilutes oxygen and stops burning at the surface of the Earth.
The next most common gas is oxygen, which is used by both animals and plants for respiration. It accounts for 21 percent of the Earth's atmosphere.
The remaining gases combined make up just one percent of the atmosphere. The largest of these is argon, but there are also variable gases like carbon dioxide, which is fourth on the list. Carbon dioxide accounts for about 0.038 percent of the gases in the atmosphere.
Other gases that can be found in even smaller amounts include water vapor, methane, sulfur dioxide, ozone and nitrogen oxides. Apart from water vapor, these gases only contain trace elements. Water vapor varies from trace elements up to as much as 0.4 percent.