Earth Atmosphere layers
The atmosphere of Earth is the layer of gases surrounding the planet Earth that is retained by Earth’s gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention, and reducing temperature extremes between day and night.
The common name air is given to the atmospheric gases used in breathing and photosynthesis. By volume, dry air contains 78.09%nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. Air content and atmospheric pressure vary at different layers, and air suitable for the survival of terrestrial plants and terrestrial animals is found only in Earth’s troposphere.
The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km is often used as the border between the atmosphere and outer space. Severallayers can be distinguished in the atmosphere, based on characteristics such as temperature and composition.
Structure of the atmosphere
In general, air pressure and density decrease with altitude in the atmosphere. Earth’s atmosphere can be divided (called atmospheric stratification) into five main layers. From highest to lowest, the five main layers are:
- Exosphere: 700 to 10,000 km (440 to 6,200 miles)
- Thermosphere: 80 to 700 km (50 to 440 miles)
- Mesosphere: 50 to 80 km (31 to 50 miles)
- Stratosphere: 12 to 50 km (7 to 31 miles)
- Troposphere: 0 to 12 km (0 to 7 miles)
The exosphere is the outermost layer of Earth’s 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. The exosphere merges with the emptiness of outer space, where there is no atmosphere.
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 exosphere is located too far above Earth for any meteorological phenomena to be possible. The exosphere contains most of the satellites orbiting Earth.
The thermosphere is the second-highest layer of Earth’s atmosphere. It extends from the mesopause (which separates it from the mesosphere) at an altitude of about 80 km up to the thermopause at an altitude range of 500–1000 km. The lower part of the thermosphere, from 80 to 550 kilometres above Earth’s surface, contains the ionosphere.This atmospheric layer undergoes a gradual increase in temperature with height. A person would not feel warm because of the thermosphere’s extremely low pressure.This layer is completely cloudless and free of water vapor.
The mesosphere is the third highest layer of Earth’s atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratopause at an altitude of about 50 km to the mesopause at 80–85 km above sea level.
Temperatures drop with increasing altitude to the mesopause that marks the top of this middle layer of the atmosphere. It is the coldest place on Earth and has an average temperature around −85 °C (−120 °F; 190 K).
It is too high above Earth to be accessible to aircraft and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets.
The stratosphere is the second-lowest layer of Earth’s atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly 12 km above Earth’s surface to the stratopause at an altitude of about 50 to 55 km.
It contains the ozone layer, which is the part of Earth’s atmosphere that contains relatively high concentrations of that gas. The stratosphere defines a layer in which temperatures rise with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet radiation (UV) radiation from the Sun by the ozone layer, which restricts turbulence and mixing. Although the temperature may be −60 °C (−76 °F; 210 K) at the tropopause, the top of the stratosphere is much warmer, and may be near 0 °C.
This is the highest layer that can be accessed by jet-powered aircraft.
The troposphere is the lowest layer of Earth’s atmosphere. It extends from Earth’s surface to an average height of about 12 km, although this altitude actually varies from about 9 km (30,000 ft) at the poles to 17 km (56,000 ft) at the equator with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion and in others by a zone which is isothermal with height.
The temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e. Earth’s surface) is typically the warmest section of the troposphere. The troposphere contains roughly 80% of the mass of Earth’s atmosphere.
Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most of Earth’s weather takes place