There is the atmosphere that is composed of 4 parts: the troposphere, the stratosphere, the mesosphere, and the thermosphere. I know that air is a gas made up of molecules. And a gas fills up the container it is contained in, which is the atmosphere. 1Most of the mass of molecules are in the troposphere, and there is ozone production in the stratosphere. Plus, there is oxygen and nitrogen in the thermosphere. But what keeps most of the molecules in the troposphere? 1There are other elements in there right?