Earth's atmosphere is divided into five main layers: the exosphere, the thermosphere, the mesosphere, the stratosphere and the troposphere.The atmosphere thins out in each higher layer until the gases dissipate in space. There is no distinct boundary between the atmosphere and space, but an imaginary line about 68 miles (110 kilometers) from the surface called the Karman line. This is usually where scientists say the atmosphere meets outer space.

More Info: space.com