<Ul> <Li> The ozone layer is contained within the stratosphere . In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere . It is mainly located in the lower portion of the stratosphere from about 15--35 km (9.3--21.7 mi; 49,000--115,000 ft), though the thickness varies seasonally and geographically . About 90% of the ozone in Earth's atmosphere is contained in the stratosphere . </Li> <Li> The ionosphere is a region of the atmosphere that is ionized by solar radiation . It is responsible for auroras . During daytime hours, it stretches from 50 to 1,000 km (31 to 621 mi; 160,000 to 3,280,000 ft) and includes the mesosphere, thermosphere, and parts of the exosphere . However, ionization in the mesosphere largely ceases during the night, so auroras are normally seen only in the thermosphere and lower exosphere . The ionosphere forms the inner edge of the magnetosphere . It has practical importance because it influences, for example, radio propagation on Earth . </Li> <Li> The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed . The surface - based homosphere includes the troposphere, stratosphere, mesosphere, and the lowest part of the thermosphere, where the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence . This relatively homogeneous layer ends at the turbopause found at about 100 km (62 mi; 330,000 ft), the very edge of space itself as accepted by the FAI, which places it about 20 km (12 mi; 66,000 ft) above the mesopause . </Li> </Ul> <Li> The ozone layer is contained within the stratosphere . In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere . It is mainly located in the lower portion of the stratosphere from about 15--35 km (9.3--21.7 mi; 49,000--115,000 ft), though the thickness varies seasonally and geographically . About 90% of the ozone in Earth's atmosphere is contained in the stratosphere . </Li> <Li> The ionosphere is a region of the atmosphere that is ionized by solar radiation . It is responsible for auroras . During daytime hours, it stretches from 50 to 1,000 km (31 to 621 mi; 160,000 to 3,280,000 ft) and includes the mesosphere, thermosphere, and parts of the exosphere . However, ionization in the mesosphere largely ceases during the night, so auroras are normally seen only in the thermosphere and lower exosphere . The ionosphere forms the inner edge of the magnetosphere . It has practical importance because it influences, for example, radio propagation on Earth . </Li> <Li> The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed . The surface - based homosphere includes the troposphere, stratosphere, mesosphere, and the lowest part of the thermosphere, where the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence . This relatively homogeneous layer ends at the turbopause found at about 100 km (62 mi; 330,000 ft), the very edge of space itself as accepted by the FAI, which places it about 20 km (12 mi; 66,000 ft) above the mesopause . </Li>

The state of atmosphere over an area at any point of time is known as