Gravitational forces from the Earth pull the air molecules in the atmosphere toward the ground. The atmosphere becomes a thin layer of air hugging the ground. Gravitational forces from the Earth pull the air molecules in the atmosphere toward the ground. The atmosphere becomes a thin layer of air hugging the ground.
In this photograph from space, the densest part of the atmosphere is the thin
blue layer sitting close to the Earth's surface. It is less than 100 km thick.
Compare this to the diameter of the Earth, which is about 13,000 km.
The atmosphere gradually fades away as we go farther and farther away from the Earth's surface. The "top" of the atmosphere, where there are practically no gas molecules, is about 300-500 km above the Earth's surface.
