If you lived in Aristotle's day you may have had strange beliefs about the atmosphere. People back then knew it existed, but they didn't really know what it was. It wasn't until centuries later that scientists understand it.
Earth is the only planet in the solar system with an atmosphere that can sustain life. All of the atmospheric layers and what are in them is described here.
The atmosphere is comprised of layers based on temperature. These layers are the troposphere, stratosphere, mesosphere, thermosphere and exosphere. This explains why the atmosphere is split into layers and what determines where the layers start and end and also what is apart of the layer.
How are atmospheric layers named once they have been discovered? Tropos (greek): turn(ing) Turbulent mixing is relevant in this layer of the atmosphere => Turbulent Mixing Sphere => Troposphere Stratum (latin): something which covers something else (pavement, blanket) This layer of the atmosphere, which is not dominated by turbulent mixing, covers the lower turbulent layer => Covering Sphere => Stratosphere Mesos (greek): middle This part of the atmosphere is the third of five (from humans defined) layers of the atmosphere => Layer in the middle (not by distance/height but by counting layers) => Mesosphere Thermos (greek): warm, heat This layer can be heated to above 1000 °C by the sun. However, it does not feel 'warm' because of the low 'air' density. => Heated/hot layer => Thermosphere Exo (greek): outside, external This layer is the most outward located layer of the atmosphere. => At the outer side located => Exosphere