NCERT Book Class 7 Social Science (Geography) Chapter 4 Air

4 Air
Do you know? Our earth is surrounded by a huge blanket of air
called atmosphere. All living beings on this earth
Carbon dioxide depend on the atmosphere for their survival. It
released in the provides us the air we breathe and protects us from
atmosphere creates a the harmful effects of the sun’s rays. Without this
green house effect by blanket of protection, we would be baked alive by the
trapping the heat heat of the sun during day and get frozen during
radiated from the night. So it is this mass of air that has made the
earth. It is therefore temperature on the earth liveable.
called a greenhouse
gas and without it the
COMPOSITION OF THE A TMOSPHERE
earth would have been
too cold to live in. Do you know that the air we take in while breathing is
However, when its actually a mixture of many gases? Nitrogen and oxygen
level in the are two gases which make up the bulk of the
atmosphere increases atmosphere. Carbon
due to factory smoke dioxide, helium,
or car fumes, the heat ozone, argon and
retained increases the hydrogen are found
temperature of the in lesser quantities.
earth. This is called
Apart from these
global warming. This
gases, tiny dust
rise in temperature
causes the snow in
particles are also
coldest parts of the present in the air. The
world to melt. As a pie chart gives you the
result the sea level percentage of different
rises, causing floods in constituents of air (Fig. 4.1).
the coastal areas. Nitrogen is the most
There may be drastic plentiful gas in the air. When
changes in the climate we inhale, we take some
of a place leading to amount of nitrogen into our
extinction of some lungs and exhale it. But
plants and animals in plants need nitrogen for their
the long run. Fig. 4.1: Constituents of Air survival. They can not take