3.1 | THE ATMOSPHERE

The atmosphere is made up of a lot of different gases. Nitrogen (78%) and oxygen (21%) are the main gases found in the atmosphere; the remaining 1% consists of a variety of other gases such as argon, carbon dioxide and hydrogen. In addition, the atmosphere is divided into 5 layers: the troposphere, stratosphere, mesosphere, thermosphere and ionosphere. Most aircraft flights take place in the troposphere, the lower layer.