Page 93 - Journeys Through Society-7

through respiration by animals, burning of fossil fuels contains 'ions' which reflect radio waves to the Earth,
and from decaying remains of plants and animals. making wireless communication possible. In the
Several other gases form the remaining part of air, upper part of this layer, brightly coloured lights known
such as water vapour which forms clouds. The clouds as aurora borealis are produced. This layer is also
bring various forms of precipitation on the Earth. known as ionosphere and is characterised by a rapid
Undesirable elements, such as soot, smoke, rise in temperature with increasing altitude.
fluorocarbons, etc., are also present in the air. These
Exosphere
elements are released into the atmosphere due to
human activities. Pollen and dust carried by winds also This layer extends to a height of about 1,600 km and
reduce the quality of air. merges into outer space. Ultraviolet rays fill this layer
and faintly glows called zodiacal lights, which occur
Layers of the Atmosphere due to sunlight reflected from particles of meteoric
The atmosphere is divided into various layers. Let us dust, originate in this layer. The thin air in this layer
study more about each layer. contains helium and hydrogen.

Troposphere

This is the lowest layer of the atmosphere and varies in
thickness from the Equator to the poles. Also, the air
which is closer to the ground is denser and gets
thinner with increasing altitude. The temperature in
this layer decreases at a rate of 1°C for every 165
metres of ascent. This is known as normal lapse rate.

Troposphere maintains temperature conditions on
the Earth and also contains important life-sustaining
gases such as nitrogen, carbon dioxide and oxygen. All
kinds of weather activities occur within the Layers of the atmosphere
troposphere. It has an average height of 16 km above
Weather and Climate
the Equator and 8 km above the poles.
Weather refers to the conditions of the air around us
Stratosphere in a small area which is subject to change in short
This layer lies just above the troposphere. It extends to periods of time. While climate refers to weather
a height of 50 km. It is a cloud-free zone and is most conditions prevailing over a long period of time.
suitable for jet planes to travel unobstructed at great Unlike weather, climate does not change. In case there
speeds. The ozone layer found here absorbs the are some changes, they occur over a long period of
harmful ultraviolet rays of the sun. In this layer, time.
temperature begins to increase with altitude. In the morning, the weather conditions may be cool
with a slight breeze but by afternoon, the weather
Mesosphere
changes and it becomes hot. In the evening, there
This layer extends to a height of 80 kilometers above might be a thunderstorm with some rainfall. The next
the Earth's surface. Here, temperature decreases with
day, there may not be a thunderstorm. Thus, we see
increase in height. This is the coldest layer with that the weather changes from time to time everyday
temperatures below -143°. Meteorites that enter the
and is not fixed, but these changes are confined only
Earth's atmosphere from outer space burn up in this to a local area. On the other hand, climate is the
layer. overall condition of the weather, the average of which

is taken over a long period of time. It does not change
Thermosphere
from day to day and covers a large area. For example,
This layer extends up to a height of 400 km. This layer
India has a tropical monsoon climate, which means it
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