The document defines key terms related to the atmosphere and its composition and structure. It defines atmosphere, weather, climate, and meteorology. It then describes the major layers of the atmosphere from lowest to highest - the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere extends from the surface to around 11 km and contains around 80% of the atmosphere. The stratosphere extends from 11-50 km and contains the ozone layer. Temperature increases with height in the stratosphere. The mesosphere and thermosphere together contain around 0.1% of the atmosphere.