Page 114 - SST Class 07

The Atmosphere
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q Composition of the atmosphere q Structure of the atmosphere
q Weather and climate q Cyclones

Introduction Oxygen is the second most plentiful gas. It helps
in combustion (burning) and oxidation. The
The atmosphere is a very significant component for
amount of carbon dioxide released by humans or
the biospheric ecosystem as life on the earth is only
animals seems to be equal to the amount used by
possible due to it. It extends up to 100 km above the plants, which makes a perfect balance. Thus,
the earth’s surface. It is a thick gaseous envelope
plants maintain a balance between oxygen and
which wraps the earth from all sides and is attached
carbon dioxide present in the atmosphere.
to the earth’s surface by gravitational force. Although carbon dioxide makes up only 0.03% of
Without it, the conditions on the earth would be
the air, yet it is a vital component of the
like that on the moon which has extremely hot days
atmosphere. It controls atmospheric temperature.
and bitterly cold nights. There would be no living
creatures without the atmosphere. Now, you must Water vapour is unique in that its concentration
understand that why we talk not to pollute it. varies from 0–4% of the atmosphere depending
on where you are and what time of the day it is. In

COMPOSITION OF THE ATMOSPHERE the cold, dry arctic regions, water vapour usually
accounts for less than 1% of the atmosphere,
The atmosphere is composed of a mix of several while in humid, tropical regions, water vapour
different gases in differing amounts. The can account for almost 4% of the atmosphere.
permanent gases whose percentages do not Water vapour content is very important in
change from day to day are nitrogen, oxygen and predicting weather.
argon. Nitrogen accounts for 78% of the
atmosphere, oxygen 21% and argon 0.9%. Gases Just Think!
like carbon dioxide, nitrous oxide, methane and
ozone are trace gases that account for about a Why is it important to maintain the balance
tenth of one percent of between oxygen and carbon dioxide?
the atmosphere. Besides
these fixed components STRUCTURE OF THE ATMOSPHERE
of the atmosphere, there Nitrogen Oxygen
78 per cent 21 per cent
are water vapour and The atmosphere can be divided into vertical layers
various impurities in the determined by the temperature changes with
atmosphere such as dust, Other gases altitudes. There is a thin buffer zone between each
smoke, salts, carbon 1 per cent of the layers.
monoxide and some Composition of the Troposphere
atmosphere
other chemicals.
The word tropo is derived from a Latin word
Nitrogen is the largest component and it is which means change . This is the sphere in which
essential for survival and growth of plants.
Contemporary Social Science-7
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