Composition and structure of the atmosphere Upsc

Structure of atmosphere

The atmosphere consists of different layers with different temperatures and densities. The density of the atmosphere is highest at the surface of the earth and as the altitude increases the density of the atmosphere decreases.

The column of the atmosphere has five different layers depending upon the condition of the temperature and they are: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere

Structure of atmosphere Upsc
column of atmosphere By Kelvinsong – Own work, CC BY-SA 3.0,

Vertical Structure of the Atmosphere


The lowermost layer of the atmosphere is Troposphere and its average height is 13 km it extends an average height of 8 km near the poles and extends 18 km at the equator.

The equator has the thickest Troposphere because in the equator the heat is transported to great heights by the strong convectional currents.

The troposphere contains water vapor and dust particles and all the climate, weather changes, and most biological activities take place in this layer the temperature troposphere decreases at the rate of 1°C for every 165m of height.

The zone which separates the troposphere and stratosphere is known as Tropopause.

The average air temperature at the tropopause is minus –80°C over the equator and about minus –45°Cover the poles.

The temperature in this region is near, constant and it is known as Tropopause.


The stratosphere lies above the Troposphere and extends up to a height of 50km. This layer does not associate with Weather or Climate Phenomena and is almost free from the clouds.

The Stratosphere has ideal conditions for flying Aeroplanes. The most important feature of the Stratosphere is, that this atmospheric layer contains a layer of Ozone Gas, that protects humans and other living beings from the harmful effects of solar rays.

The mesosphere lies above the stratosphere, which extends up to a height of 80 km.

In this layer, once again, the temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80km.

The upper limit of the mesosphere is known as menopause. The ionosphere is located between 80 and 400 km above the mesopause. It contains electrically charged particles known as ions, and hence, it is known as the ionosphere.

Radio waves transmitted from the earth are reflected back to the earth by this layer.

The temperature here starts increasing with height. The uppermost layer of the atmosphere above the thermosphere is known as the exosphere.

This is the highest layer but very little is known about it. Whatever contents are there, these are extremely rare in this layer, and they gradually merge with outer space.

Although all layers of the atmosphere must be exercising an influence on us, geographers are concerned with the first two layers of the atmosphere.

Elements of Weather and Climate

The main elements of the atmosphere which are subject to change and which influence human life on earth are temperature, pressure, winds, humidity, clouds, and precipitation.


1.What is the uppermost layer of the atmosphere?

The uppermost layer of Earth’s atmosphere is called the exosphere. It extends from about 600 kilometers (373 miles) to roughly 10,000 kilometers (6,213 miles) above Earth’s surface. The exosphere is a very thin and rarefied layer, with air pressure being extremely low. It is the transition zone between Earth’s atmosphere and outer space.

In the exosphere, atoms and molecules are so far apart that they rarely collide with each other. This means that the exosphere is very dynamic, with atoms and molecules constantly escaping into space and others being replaced by new ones from the lower atmosphere.

The exosphere is also where the auroras (Northern and Southern Lights) are formed. These colorful displays are caused by charged particles from the sun interacting with the Earth’s atmosphere.

2. Which is the thickest layer of the atmosphere?

This actually depends on how you define “thickest”! Let’s explore both interpretations:

By height:

  • The clear winner here is the exosphere, the outermost layer extending from about 375 miles (600 km) to a fuzzy boundary around 6,200 miles (10,000 km). It’s a vast and diffuse region, technically part of our atmosphere but with minimal density.

By density:

  • In terms of concentrated air molecules, the troposphere takes the crown. This lowest layer, hugging the Earth’s surface up to around 6 miles (10 km), packs in about 80% of the atmosphere’s total mass. It’s where we experience weather, with its denser air allowing for clouds, precipitation, and the life-sustaining conditions we know.
* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.