Exosphere

The exosphere is a layer of the atmosphere. It is the outermost layer and is very thin. It is like a fence around the earth. The exosphere is the highest layer and starts where air stops. Even the air in the exosphere is so thin that it doesn't have enough air molecules to reflect the light. That's why it is very hard to see the exosphere. Hot gases like Oxygen and Hydrogen can travel through the exosphere into outer space.