Earth's Atmospheric Layers

 Layers of the Atmosphere

» The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity.
» The atmosphere of Earth protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).
» The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.
» Earth's atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere.
» The exosphere gradually fades away into the realm of interplanetary space.
» Following is the Table of gaseous composition of dry air
Major constituents of dry air, by Volume
in ppmv(B)
in %
Carbon dioxide
Not included in above dry atmosphere:
Water vapor(C)

(A) volume fraction is equal to mole fraction for ideal gas only,
    also see volume (thermodynamics)
(B) ppmv: parts per million by volume
(C) Water vapor is about 0.25% by mass over full atmosphere
(D) Water vapor strongly varies locally

Structure of the atmosphere (Different Layers Drawing)

» Earth's atmosphere can be divided (called atmospheric stratification) into five main layers. Excluding the exosphere, Earth has four primary layers, which are the troposphere, stratosphere, mesosphere, and thermosphere. From highest to lowest, the five main layers are:
1.  Exosphere: 700 to 10,000 km (440 to 6,200 miles)
2. Thermosphere: 80 to 700 km (50 to 440 miles)
3. Mesosphere: 50 to 80 km (31 to 50 miles)
4. Stratosphere: 12 to 50 km (7 to 31 miles)
5. Troposphere: 0 to 12 km (0 to 7 miles)


·  The troposphere starts at the Earth's surface and extends 8 to 14.5 kilometres high (5 to 9 miles). This part of the atmosphere is the most dense.
·  It contains 75% of the atmosphere's mass. The troposphere is wider at the equator than at the poles.
·  Temperature and pressure drops as you go higher up the troposphere.
·  Nearly all atmospheric water vapour or moisture is found in the troposphere, so it is the layer where most of Earth's weather takes place. It has basically all the weather-associated cloud genus types generated by active wind circulation, although very tall cumulonimbus thunder clouds can penetrate the tropopause from below and rise into the lower part of the stratosphere.
·  Most conventional aviation activity takes place in the troposphere, and it is the only layer that can be accessed by propeller-driven aircraft.


·  The stratosphere starts just above the troposphere and extends to 50 kilometres (31 miles) high.
·  The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer.
·  The stratosphere is warmer at the top than the bottom. The lower portion has a nearly constant temperature with height but in the upper portion, the temperature increases with altitude because of absorption of sunlight by ozone.
·  This temperature increase with altitude is the opposite of the situation in the troposphere.
·  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


·  The mesosphere is the third highest layer of Earth's atmosphere, occupying the region above the stratosphere and below the thermosphere.
·  The mesosphere starts just above the stratosphere and extends to 85 kilometres (53 miles) high.
·  Meteors burn up in this layer.
·  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).
·  Just below the mesopause, the air is so cold that even the very scarce water vapour at this altitude can be sublimated into polar-mesospheric noctilucent clouds. These are the highest clouds in the atmosphere and may be visible to the naked eye if sunlight reflects off them about an hour or two after sunset or a similar length of time before sunrise.
·  The mesosphere is also the layer where most meteors burn up upon atmospheric entrance.
·  It is too high above Earth to be accessible to jet-powered aircraft and balloons, and too low to permit orbital spacecraft.
·  The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft.


·  The thermosphere is the second-highest layer of Earth's atmosphere. The thermosphere starts just above the mesosphere and extends to 600 kilometres (372 miles) high.
·  Aurora and satellites occur in this layer.
·  The temperature of the thermosphere gradually increases with height. Unlike the stratosphere beneath it, wherein a temperature inversion is due to the absorption of radiation by ozone, the inversion in the thermosphere occurs due to the extremely low density of its molecules.
·  This layer is completely cloudless and free of water vapour. However, non-hydrometeorological phenomena such as the aurora borealis and aurora australis are occasionally seen in the thermosphere.
·  The International Space Station orbits in this layer, between 350 and 420 km (220 and 260 mi).


·  The ionosphere is a region of Earth's upper atmosphere, from about 60 km (37 mi) to 1,000 km (620 mi) altitude, and includes the thermosphere and parts of the mesosphere and exosphere. It is ionised by solar radiation, plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.
This dynamic region grows and shrinks based on solar conditions and divides further into the sub-regions: D, E and F; based on what wavelength of solar radiation is absorbed.
·  The ionosphere is a critical link in the chain of Sun-Earth interactions.
·  This region is what makes radio communications possible.


·  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.
·  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 kilometres 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.
·  The exosphere is located too far above Earth for any meteorological phenomena to be possible. However, the aurora borealis and aurora australis sometimes occur in the lower part of the exosphere, where they overlap into the thermosphere.
·  The exosphere contains most of the satellites orbiting Earth.

See also:
Frequently Asked Questions:

What are the four different layers of the atmosphere?
The atmosphere is comprised of layers based on temperature. These layers are the troposphere, stratosphere, mesosphere and thermosphere. A further region at about 500 km above the Earth's surface is called the exosphere.

Which atmospheric layer is directly above the troposphere?
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 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 (7.5 mi; 39,000 ft) above Earth's surface to the stratopause at an altitude of about 50 to 55 km (31 to 34 mi; 164,000 to 180,000 ft).

How high is the Earth's atmosphere?
Earth's atmosphere is about 300 miles (480 kilometres) thick, but most of it is within 10 miles (16 km) the surface. Air pressure decreases with altitude. At sea level, air pressure is about 14.7 pounds per square inch (1 kilogram per square centimetre).

Why does the temperature drop in the mesosphere?
Within the mesosphere, temperature decreases with increasing height, due to decreasing solar heating and increasing cooling by CO2 radiative emission. The top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere.

Which layer of the Earth's atmosphere has the lowest air pressure?

What part of the atmosphere contains 75 percent of the atmospheric gases?

Which gas is responsible for the temperature inversion in the stratosphere?
The atmospheric gas responsible for the temperature inversion in the Stratosphere is Ozone. The reason for the inversion in the stratosphere is that the gas ozone plays a major part in heating the air at this altitude. Recall that ozone is important because it absorbs energetic ultraviolet (UV) solar energy.

What layer of the atmosphere do satellites orbit the earth?
Exosphere. This is the outermost layer of the atmosphere. It extends from the top of the thermosphere to 6,200 miles (10,000 km ) above the earth. In this layer, atoms and molecules escape into space and satellites orbit the earth.

Which is the thickest layer of the atmosphere?
The troposphere is the thickest layer of the atmosphere. It is the first of the five layers of the atmosphere, and it is just above the surface of the Earth. The troposphere contains 99% of the Earth's water and 75% of its atmosphere.

Why radio waves are reflected by ionosphere?
The low-frequency end of the window is limited by signals being reflected by the ionosphere back into space, while the upper limit is caused by absorption of the radio waves by water vapour and carbon dioxide in the atmosphere.

Where is the magnetosphere?
In the upper regions of the ionosphere, beginning several hundred kilometres above Earth's surface and extending tens of thousands of kilometres into space, is the magnetosphere, a region where the behaviour of charged particles is strongly affected by the magnetic fields of Earth and the Sun.

What is the sky wave propagation?
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere.

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