Thursday 10 December 2015

Geography For SSc Exam



Details of The Earth's Atmosphere

AIR
The blanket of air that surrounds the earth is called “Atmosphere”.
It is composed of mixture of gases. Water vapour, dust particles, pollen grains, impurities such as smoke, salts and other chemicals.
The constituent gases are:
1.Nitrogen (78%)
2.Oxygen (21%)
3.Carbon-di-oxide, argon, hydrogen, helium, ozone etc. make up the remaining 1%.
The scientific study of the processes and the physical phenomenon taking place in the earth’s atmosphere is called “Meterorology”.
Approximately the atmosphere extends upto 1600 Kilometres above the surface of the earth.
The density of the atmosphere is the highest near earth’s surface.
On the basis of the composition, temperature and other properties, the atmosphere is divided into 5 layers. Starting from the surface of the earth, the layers are:

1)Troposhpere
a)Lowest layer of the atmosphere
b)It extends to a height of 8 Kms at poles and 18 Kms at equator
c)Dust particles, water vapour and other impurities are found here
d)All weather phenomena such as clouds, fog, rainfall, snowfall and lightening occur here.
e)Temperature in this zone drops with height at the rate of 1 ͦ C for every 165m. This is normal lapse rate.
f)This layer keeps the earth warn as it absorbs maximum heat radiated by earth’s surface being the densest and lowest layer of atmosphere.

2)Stratosphere
a)Lies above the troposphere and extends to a height of 50 Kms.
b)This layer is free of clouds and associated weather phenomenon.
c)Contains ozone layer which absorbs the harmful ultra-violet rays of the sun
d)Supersonic aircraft fly in this region

3)Mesosphere
a)3rd layer of atmosphere extends to a height of 80 Kms
b)Meteorites burn up in this layer on entering from the space

4)Thermosphere
a)In this zone, the temperature increases rapidly with height
b)This layer contains “Ions” – electrically charged particles which reflect radio waves back to earth’s surface and thus enable us to have wireless communication. Thermosphere is also called Ionosphere.

5)Exosphere
a)Upper most layer with thin layer of air
b)Light gases like helium, hydrogen float into the space from here

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