This document summarizes the composition and layers of the Earth's atmosphere. It discusses the main gases that make up the atmosphere, including nitrogen, oxygen, carbon dioxide, and water vapor. It then describes the different layers of the atmosphere from lowest to highest: 1) The troposphere, where weather occurs and contains around 80% of the atmosphere's mass. 2) The stratosphere, where temperature increases with altitude due to ozone absorbing UV rays. It contains the ozone layer which protects the Earth. 3) The mesosphere, where temperature decreases with altitude. 4) The thermosphere, where temperature increases with altitude due to solar radiation. 5) The exosphere