Thermosphere

Thermosphere, outermost layer of the earth's atmosphere, at altitudes between approximately 53 mi (85 km) and 300 mi (480 km). The heat, caused by radiation of the sun, varies from −135°F (−93°C) at the lowest altitude to 2,700°F (1,500°C) and more at the highest altitude. The thermosphere is different from the layers of the atmosphere closest to earth in that the pressure is much lower (1 million times lower than at sea level) and the chemical makeup includes mostly atoms of helium and hydrogen.

See also: Atmosphere