<Li> Stratosphere: 12 to 50 km (7 to 31 miles) </Li> <Li> Troposphere: 0 to 12 km (0 to 7 miles) </Li> <P> The exosphere is the outermost layer of Earth's atmosphere (i.e. the upper limit of the atmosphere). It extends from the exobase, which is located at the top of the thermosphere at an altitude of about 700 km above sea level, to about 10,000 km (6,200 mi; 33,000,000 ft) where it merges into the solar wind . </P> <P> This layer is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase . The atoms and molecules are so far apart that they can travel hundreds of kilometers without colliding with one another . Thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space . These free - moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or the solar wind . </P>

What is the outermost layer of the atmosphere called