Atmosphere notes | Social studies for otet/osstet/JT/CHT/CTET/ Competitive exams

 Atmosphere - Components and structure of Atmosphere. Study notes for all competitive Examination. 

The composition and structure of the atmosphere

 

The air which surrounds the earth is called the atmosphere. The atmosphere is held to the earth due to its gravitational pull. The total weight of earth atmosphere is about 500 million tons. The atmosphere is essential for the existence of life on earth.

Composition of the atmosphere

The atmosphere is a mixture of colourless,  odourless and tasteless gases. The atmosphere contains two main gases oxygen ( 21%) and Nitrogen (78%).

Other gases found in small quantities include Argon carbon dioxide, neon,, hydrogen, helium, methane etc.

Besides these gases the lower layer of the atmosphere contains  water vapour,  dust particle, smoke, salt etc.

Heavier gas like oxygen is mostly found in the lower layer. All living organisms need oxygen to breath.

Nitrogen helps in the growth of living organisms.

 Carbon dioxide absorbs the heat radiated by the earth and keeps the planet warm. Plants use carbon dioxide to prepare food through the process of photosynthesis.

 

Structure of the atmosphere

 

The atmosphere has a layered structure. On the basis of composition, density, temperature and other properties the atmosphere can be divided into five layers –

Troposphere

 Stratosphere

 Mesosphere

 Thermosphere

 Exosphere

 

Troposphere

The troposphere is the lowest layer and is closest to the earth’s surface.

It extends  up to a height of about 8 km near the poles and about 18 km over the equator.

This layer protects us from the excessive heat of the sun during the day and keeps the earth’s surface warm at night.

The troposphere is the home of clouds, lightning, thunderstorm and other weather phenomenon.

With increase in height the temperature decreases at rate of 1° C per 165m of ascent called normal lapse rate.

Troposphere has about 90% of the air in the atmosphere.  Water vapour and dust particles are found only in this layer of atmosphere

 

Stratosphere

Stratosphere lies above the troposphere and it spread about 50 kilometre above the sea level.

 The lower part of the stratosphere between 15 km to 35 km has concentration of ozone and is thus called ozonosphere.

Ozone act as a barrier for ultraviolet radiation of the sun to reach the earth’s surface add protect life on earth.

 

Mesosphere

The mesosphere lies above the stratosphere. It extends from about 50 km to about 80 km above the mean sea level.

This is the coldest layer in the atmosphere.

 Meteors which comes from outer space burn up in this layer because of friction with the atmosphere.

The temperature decreases with height and reaches about -100° C at the heights of 80km.

 

Thermosphere

The Thermosphere lies above the mesosphere. It extends from about 80 km to about 400 km above the mean sea level.

The lower part of the Thermosphere is called ionosphere as it has  Ionized molecules.

In the thermosphere the temperature may  reach up to 1500°C at it’upper limit.

This layer reflects low frequency radio waves to earth. Thus It helps in long distance communication.

Exosphere

The exosphere is the uppermost layer.

 The density of air is very low and it is in a rarefied form.

Very light gases like hydrogen and helium are found in this layer.

 The exosphere merges is gradually into outer space.