Atmosphere Layers, Structure, Composition, Importance

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What Is Atmosphere?

The atmosphere is the gaseous layer that surrounds the earth and marks the transition between its surface and space, It is made up of numerous gases such as nitrogen , oxygen and carbon dioxide etc. Some scientists stated that the atmosphere i

s about 35 years old; its thickness is about 10,000 kilometres. However, the atmosphere consists of a mixture of gases, it is composed of 78% of nitrogen, 21% of oxygen, and other minor elements which makes up the remaining 1% including argon, helium, carbon dioxide, and water vapour. The little amount of carbon dioxide in the atmosphere is a critical component in the regulation of the earths temperature.

The atmosphere extends over three hundred miles above the earths surface, and the lower level makes up the earths climatic system. This lowest level is called the troposphere and it is responsible for the conditions that allow life to exist on the earths surface.

About 97 percent of the total atmosphere remains restricted within 30 kilometres upward from the earths crust. The atmosphere remains in contact with the earths crust due to the gravitational attraction. Due to the pressure of the layers of the atmosphere, density of air is highest at the sea level and decreases with height. The part of the atmosphere that is relevant is the troposphere which is about 10 km on the average.

Layers of atmosphere

The atmosphere is divided vertically into four layers according to the characteristics of its different elements (temperature, pressure, density) these include:

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere


Troposphere is the lowest layer of the atmosphere, it is a layer of the atmosphere that is much relevant for weather and climate. This layer remains in contact with the earth crust. Throughout this layer there is a general decrease in temperature at a mean rate of 6.5C/km. This whole zone is capped by a temperature inversion layer, the tropopause, which acts as a covering on the troposphere and on weather; tropopause separates the troposphere from the stratosphere. The upper limit of the troposphere instead of terminating immediately, its characteristics gradually fade away and mix up with the next stratosphere layer. The troposphere is about 8 km thick in the polar region and 16 to 19km thick in the equatorial region. It is made up of numerous gases such as nitrogen, oxygen and carbon dioxide. The most variable component of the troposphere are water vapour closer to the ground and also closer to the equator the quantity of dust particles vary more than that of the water vapour. some characteristics of the troposphere include :

  • In this layer, there is a decrease in density and temperature due to increase in altitude.
  • The decrease of temperature with increase of altitude is known as the normal lapse rate.
  • The lower atmosphere contains water vapour.
  • All sorts of weather and climatic activities take place in this layer.
  • The velocity of the wind increases with the increases of altitude.
  • The wind moves upward and downward.


Stratosphere is the second layer of the atmosphere which contains no water vapour, it extends upward to 50 kilometres. A high amount of ozone gas is available in this layer hence, the stratosphere is the area of ozone concentration. Ozone layer absorbs maximum ultraviolet rays of the sun from reaching the earth surface since the concentration of the ultraviolet radiation may cause danger to living things. So, the prevention of ultraviolet rays from reaching the earths surface in high intensity is a welcome relief to many living organisms. Both density and pressure are comparatively less in this layer and the temperature also does not show a change in the lower atmosphere, maximum temperature occur on the stratosphere just immediately above the stratosphere. However, from the 20th kilometre upwards, the temperature records a gradual rise and continues up to 50 kilometres in the high stratosphere, the gradual rise in temperature is due to the relative low density of the air at this height.


Mesosphere is the third layer of the atmosphere which extends to a height of 5080 km in space and it is characterized by small lapse rate. The temperature reduce rapidly from the stratosphere upwards up to 80 kilometres to a minimum of -900C. Above 80 kilometer, temperature increases again, this is due to ozone and oxygen molecules absorption of radiation. The layer where this occur is known as mesopause. Air pressure is very thin in mesosphere, decreasing from 1 mb at 50 km to 0.01 mb at 90 km (surface pressure is about 1,000.mb).


Thermosphere is another layer of the atmosphere, it extends upward from the mesopause into space. This layer can possess very high gas temperatures due to the bombardment by energetic solar radiation. The lower part of the thermosphere is known as ionosphere. Above the ionosphere, there are other two layers such as exosphere and magnetosphere.

Diagram showing the four layers of the atmosphere
Diagram showing the four layers of the atmosphere


Structure and composition of the atmosphere

Atmosphere is constituted by the mixture of several gases. The composition of the atmosphere remains fairly constant roughly up to an altitude of 80 kilometres. Nitrogen and oxygen are the two main components of the atmosphere and their constituents are purely dry air as long as the volume is concerned. Both of these gases have important relationship with living things. Nitrogen is removed from the atmosphere and deposited at the Earth’s surface mainly by specializednitrogen fixingbacteria, and by way oflightningthrough precipitation. The addition of this nitrogen to the Earth’s surface soilsand various water bodies supplies much needed nutrition for plant growth. Nitrogen returns to the atmosphere primarily through biomass combustion anddenitrification. On the other hand, oxygen is exchanged between the atmosphere and living things through the processes ofphotosynthesisandrespiration. Photosynthesis produces oxygen when carbon dioxide and water are chemically converted into glucose with the help of sunlight. Respiration is at the opposite process of photosynthesis. In respiration, oxygen is combined with glucose to chemically release energy for metabolism. The outcome of this reaction are water and carbon dioxide.

Nitrogen contains 78.02% and oxygen contains 20.71%, however, these two gases when combined constitute about 98.73% and the remaining 1.27% is being occupied by other gases. Below is the list of the composition of elements.

Composition of the the atmosphere
Composition of the the atmosphere


Other gases include helium, krypton, xenon, hydrogen, methane, and nitrous oxide. but a variable amount of water vapor is also present on average about 1% at sea level; water vapor varies in concentration in the atmosphere both spatially and temporally. The highest concentrations of water vapor are found near the equator over the oceans and tropical rain forests. Cold polar areas and subtropical continental deserts are locations where the volume of water vapor can approach zero percent.

The amount of carbon dioxide in the atmosphere is only about 0.03 per cent; this little amount of carbon dioxide in the atmosphere is much important for the atmospheric processes, this is because gas helps the short waves of the suns rays to reach the earth. The short waves rays after coming in contact with the earths surface transform themselves to long waves. Carbon dioxide absorbs these long waves in the lower atmosphere. As a result, the atmosphere becomes hot.

Importance of atmosphere

The atmosphere is of great importance to both man and other living organisms

  1. The atmosphere provides nitrogen in which plants used to build up protein contents
  2. It provides gases which are essential for respiration.
  3. It contains ozone layer which acts as a protective cover for living organism against the burning effects of ultraviolet rays of the sun.
  4. The atmosphere serves as the habitat for some living organisms.
  5. The changes in the atmosphere condition is what modify the weather and climatic activities in our surroundings.