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The Layers of Earth's Atmosphere

Exosphere

The exosphere is the highest layer of the atmosphere. It extends from the top of the thermosphere up to 10,000 km (6,200 mi; 33,000,000 ft).

This is the upper limit of our atmosphere. The atmosphere here merges into space in the extremely thin air. Air atoms and molecules are constantly escaping to space from the exosphere. In this region of the atmosphere, hydrogen and helium are the prime components and are only present at extremely low densities. This is the area where many satellites orbit the Earth. The exosphere contains free-moving particles that may migrate into and out of the magnetosphere or the solar wind.


Thermosphere

The thermosphere (literally "heat sphere") is the outer layer of the atmosphere, separated from the mesosphere by the mesopause. It extends from the top of the mesosphere to over 640 km (400 mi; 2,100,000 ft).

Within the thermosphere temperatures rise continually to well beyond 1000 degrees C. The few molecules that are present in the thermosphere receive extraordinary amounts of energy from the Sun, causing the layer to warm to such high temperatures. Although the measured temperature is very hot, the thermosphere would actually feel very cold to us because the total energy of only a few air molecules residing there would not be enough to transfer any appreciable heat to our skin.

The lower part of the thermosphere, from 80 to 550 km above the Earth's surface, contains the ionosphere. Beyond the ionosphere extending out to perhaps 10,000 km is the exosphere or outer thermosphere, which gradually merges into space.Temperature increases with height. Although the temperature can rise to 1,500 degrees C (2,730 degrees F), a person would not feel warm because of the extremely low pressure. The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi).


Mesosphere

The mesosphere is the third highest layer in our atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the top of the stratosphere to the range of 80 to 85 km (50 to 53 mi; 260,000 to 280,000 ft).

Temperatures in the mesosphere drop with increasing altitude to about -100 degrees Celsius (C). The mesosphere is the coldest of the atmospheric layers. In fact it is colder then Antarctica's lowest recorded temperature. It is cold enough to freeze water vapor into ice clouds. You can see these clouds if sunlight hits them after sunset. They are called Noctilucent Clouds (NLC). NLCs are most readily visible when the Sun is from 4 to 16 degrees below the horizon. The mesosphere is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere. From the Earth they are seen as shooting stars.


Stratosphere

The second lowest layer of Earth's atmosphere, it lies above the troposphere and is separated from it by the tropopause. It extends from the top of the troposphere to about 50 km (32 mi; 170,000 ft).

The stratosphere contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone. The stratosphere defines a layer in which temperatures rises with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet (UV) radiation from the Sun by the ozone layer. Such a temperature profile creates very stable atmospheric conditions, and the stratosphere lacks the air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds or other forms of weather.


Troposphere

The lowest layer of Earth's atmosphere. It extends from Earth's surface up to 7 km (23,000 ft) at the poles, and about 17-18 km (56,000 ft) at the equator.

The troposphere is bounded above by the tropopause, a boundary marked by stable temperatures. Although variations do occur, temperature usually declines with increasing altitude in the troposphere.

The troposphere is denser than the layers of the atmosphere above it (because of the weight compressing it), and it contains up to 75% of the mass of the atmosphere. Fifty percent of the total mass of the atmosphere is located in the lower 5.6 km (18,000 ft) of the troposphere. It is primarily composed of nitrogen (78%) and oxygen (21%) with only small concentrations of other trace gases. Nearly all atmospheric water vapor or moisture is found in the troposphere. The troposphere is the layer where most of the world's weather takes place.


Image courtesy of NOAA on Wikipedia Commons