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2. Structure of the Earth
What does it consist of?

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5. Our earth is surrounded by an envelop of gases.
This blanket of gases hanging over our earth is called
ATMOSPHERE.
It is integral part of our earth like lithosphere and hydrosphere.
Pure air is colourless, odourless, tasteless and not to be felt unless it
is in motion.
It is mobile compressible and expansible and has weight.
About half the mass of atmosphere lies below the height of 5500
meters and about 99 percent lies below 40 kms.
Life is impossible without atmosphere. There will not no weather and
climate without it.
It protects us from the full range of solar effects.
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6. Air or atmosphere is a mixture of some gases.
Only 4 gases namely nitrogen (78.084%), oxygen (20.947%),
argon (0.934%) and carbon dioxide (0.031%) account for 99% of
dry air.
Oxygen
 No life is possible without it
 Necessary for combustion
 Necessary for animal metabolism
 Constitutes one fifth of the dry air
 It is replenished by photosynthesis in plants
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7. Nitrogen
 Important constituent for many organic compounds
 Most important function is to dilute oxygen and regulate
combustion and oxidation
Carbon dioxide
 Green plants extract carbon dioxide from atmosphere for
photosynthesis
 Has great climatic significance
 Efficient absorber of heat and emits half of the heat absorbed to
earth.
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8. Ozone
 It absorbs ultraviolet radiation and protects us from full range of
solar effects.
Water vapor
 The atmospheric moisture causes precipitation, in different forms
like rain, hail, fog, mist, snow etc.
 It causes rainbow
 It causes halo around sun and moon
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9. Some important characteristics of atmosphere
 Denser gases predominate the lower layers. This is due to
gravitational pull exercised by earth.
 Carbon dioxide disappears at the height of 20km, oxygen at 110 km
and nitrogen at 130 km . Beyond the height of 80 km atmosphere
mainly consists of hydrogen.
 There is horizontal variation in atmosphere also. Heavier gases are
least over equator and predominate polar areas.
 The composition of atmosphere is fairly uniform upto the height of 6
km
 The contents of water vapor vary with temperature. The % decreases
from equator towards pole
 The composition changes during daytime. At noon, light gases
predominate..
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10. Generally four different layers of atmosphere are recognized:
 Troposphere
 Stratosphere
 Mesosphere
 Thermosphere
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11.  Derived from greek word tropos meaning mixing
 Height places from place to place and season to season. Generally its
height is 17 kms over equator and 8 km over poles.
 Average altitude is 11 kms
 Clouds, storms, cyclones, dust particles and water vapours are confined to
this layer.
 The temperature decreases with height at the rate of 6.5 degree celsius for
every 1000 meters. This is called lapse rate.
 The temperature in this layer ranges upto -56 degree celsius
 This layer contains nitrogen, oxygen, carbon dioxide and water vapour.
 75% of the mass of atmosphere lies in this layer.
 A shallow layer called ‘ tropopause’ ( = where mixing stops) marks its
upper limit
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12. The layer above tropopause is called stratosphere
The temperature in the lower layers is constant and the lower layer
is called ‘isothermal layer’.
Beyond that the temperature increases due to absorption of
ultraviolet rays by ozone.
The temperature comes upto – 2 degree celsius
There are no clouds, no dust particles, no water vapour, no
cylcones, no storms and no convection currents in stratosphere.
The layer goes upto the height of 50 km
Ozone dominates this layer
A shallow layer of stratopause marks its upper layer.
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13.  There is maximum concentration of ozone from 30-60 km above the
surface of earth.
 It is a warm layer as ozone absorbs extremely hot ultra violet rays.
 This absorption protects the man from sun burn and many other
diseases and health problems which can happen due to ultra violet
rays.
 Its formation starts at an altitute of 16 km from the surface of earth.
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14.  The layer at an altitude of 50-80 km is called mesosphere.
 The temperature decreases with height and reaches -92ºC
at the height of 80 km. Beyond this height the temperature
increases rapidly.
 Thermosphere also known as ionosphere is the highest
layer.
 It extends from 80 to 500 kms in height
 It is of greatest interest as it reflects radio waves.
 The temperature in this layer reaches upto 1200ºC
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15.  Ionosphere has been divided into ionised layers:
• D-Layer: it reflects low frequency radio waves. It disappears with
sunset . It extends from 60-99 km
• E-Layer: It is also called kenelly heaviside layer. It reflects
medium and high frequency radio waves. It disappears in night
and extends from 90 -130 km.
• Other layers are sporadic E-layer, E2, F1, F2 and L1 layers.
 Study of troposphere and stratosphere is a subject of Meteorology
 Study of mesophere and thermosphere is called Aerology
 Some meteorologists call the outer layer, 500-100 km, as Exosphere.
Hydrogen and helium predominate this layer.
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17.  The liquid layer of the Earth is called the hydrosphere.
 It represents the entire conglomeration of water bodies enveloping the
earth's surface. The hydrosphere consists of the rivers, streams, lakes
and oceans, while its sub-category, the cryosphere, is made up of the
temporarily frozen, solid water bodies such as ice, snow and glaciers.
 Hydrosphere which extends over 70% of the earth’s surface, is the major
source of water.
 The water reaches the land through a process called water cycle. (
discussed in previous lectures.)
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18.  The Sun's heat evaporates the water of the hydrosphere.
 The newly-created water vapor rises into the atmosphere, cools,
condenses, and becomes precipitation, falling back onto the land and
into the oceans, lakes, and rivers.
 The hydrologic cycle describes the movement of water in its three
states: solid, liquid and gas. The evaporation and precipitation of the
water, the hydrosphere of planet Earth, recycles and rejuvenates the
Earth and its water supply each and every day.
 Evaporation and precipitation across the Earth is in total balance,
though evaporation is greater than precipitation over the oceans and
the reverse is true over the land.
 Water vapor usually averages twelve days in the atmosphere before
coming back down to Earth again as rain or snow. This difference is
corrected by the flow of rivers into the oceans and balance is
maintained.
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19. Simple block diagram of water cycle/hydrocycle
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20. Major sources of water:
 Rain water
 Surface water in the form of gullies streams, rivers, ponds, lakes
 Ground water is the water that remains under the earth’s crust in the
form of ground water storage.
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21. Major uses of water are
Municipal use/ domestic use
drinking water purposes, washing flushing toilets, garden irrigation, air
coolers etc.
Water for Industry:
There are many industries which use huge quantities of water e.g. iron and
steel, jute, paper, fertilizer etc.
Water in Agriculture:
Water is used for irrigating the agricultural areas.
Water for generating Power
to generate hydroelectric power
Other uses:
navigation, fisheries, swimming, boating, water skiing etc.
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