Below is the summary of class 7 geography chapter 4 named as Air. Our earth is surrounded by a blanket of air which is known as Atmosphere. This atmosphere protects us from the harmful radiation of the sun.
Human beings and other living organisms on the earth are surviving because of the atmosphere because it provides us the air to breathe.
Composition of the Atmosphere
About 99% of the Atmosphere is Nitrogen and oxygen. They are 78% and 21% respectively. Other gases present in the air are Carbon dioxide, Argon, helium, hydrogen, etc.
Nitrogen is available in abundance. Human beings do not use Nitrogen, but it is important for the survival of the plants.
They do not take it directly rather Bacteria that live in the soil and roots, make it usable by taking it through the soil.
Around 21% part of the air is oxygen. It is important for the survival of Human beings. A person can barely live more than a minute without inhaling oxygen.
Plants produce oxygen through the process of photosynthesis. To maintain the balance of oxygen in the atmosphere we need to stop cutting trees.
Carbon Dioxide (CO2) is also a very important gas in the atmosphere. Though it is less than 0.03% of the atmosphere, Countries are seeking ways to reduce the amount of this.
Significance of Carbon Dioxide
- Plants use CO2 for the process of photosynthesis. Intern, they produce oxygen.
- CO2 helps in keeping the earth warm. It is a greenhouse gas that traps the incoming heat radiations of the sun.
Structure of the Atmosphere (Class 7 geography chapter 4)
From the Earth’s surface, the Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere are the five layers of our atmosphere. Temperature changes with change in height but changes differently in each layer.
This layer is the most important layer for living organisms. The air we breathe is available only in this layer. the composition of oxygen reduces with an increase in height.
This layer extends up to an average height of 13 km. The height is more in the equatorial region than the polar region. All the weather phenomena occur in this layer.
The temperature in the troposphere decreases with an increase in height.
Stratosphere extends up to the height of 50 km. It is favourable for flying airplanes because it has no weather phenomenon associated.
This layer also contains the ozone layer which saves our environment from harmful UV radiations of the sun.
The temperature in this layer increases with an increase in height.
This is the middle layer of the atmosphere. Mesosphere lies above the stratosphere and extends up to the height of 80 km. Several meteorites coming towards earth burn up in this layer.
The temperature decreases with an increase in height.
This layer extends between the range of 80 to 400 km. It helps in the transmission of radio waves.
The temperature in this layer rises rapidly with an increase in height.
Some part of this layer is also known as Ionosphere.
This is the outermost layer of the atmosphere. This layer has very thin air and contains light gases such as helium and hydrogen.
The temperature in this layer also rises with an increase in height.
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