The layer above the thermosphere which extends beyond 720 km from the earth surface is called exosphere. It is the outermost layer of earth atmosphere which bounds the other four inner layers so it is also called fringe region. Here, molecules are less in number but temperature varies from 1200°C to 6000°C.
The air in exosphere is very thing and it is made up of helium and hydrogen and the traces of other gases such as atomic oxygen and carbon dioxide. The upper level of the exosphere is the farthest point from earth that is still affected by earth's gravity.