The atmosphere can be divided into layers based on temperature variations, which is the basis for dividing the atmosphere into four layers. These layers are the troposphere, stratosphere, mesosphere, and thermosphere. The temperature gradient of each layer is different, and in some layers, temperature increases with altitude, while in others, it decreases. The troposphere is the layer closest to the Earth and contains about 75% of all the air in the atmosphere and almost all of the water vapor. The stratosphere is the layer above the troposphere and contains the ozone layer, which absorbs most of the suns harmful ultraviolet radiation. The mesosphere is the layer above the stratosphere, and the thermosphere is the layer above the mesosphere. The exosphere is the outermost layer of the atmosphere, and there is no real outer limit to it. By understanding how the atmospheres temperature changes with altitude, we can learn how the atmosphere works.