Social Science
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WHAT
IS
AROUND
US
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?
Dhanvin was roaming in the garden with his mother. While walking, a question arouse in his
mind. The land on which we are walking, how it would have been made ? Dhanvin asked this
question to his mother. Mother said, “Everyday you see the sun ? The sun also has a family,
which is known as ‘solar family’. Our earth is one of the members of this solar family. The most
important point is that, only earth has got the convinient temperature, water and air for the life
sustaining of living beings. No evidence has been found till date regarding such convinience of
living on any other member of solar family.”
Generally it is believed that, earth has been detached from sun. At the time of its origin. it
was in the form of fireball. This fireball started to cool down slowly. Many elements of earth got
transformed into liquid and further it got transformed into solid form. During this process, the
elements which got transformed into solid form is known to us as Lithosphere. The elements
which got transformed into liquid form, is the Hydrosphere. The elements, which tranformed
into gaseous state, came to be known as Atmosphere. Above all, the development of living world
was possible due to land and its crust, water to drink, air to breathe and it is known as Biosphere.
In this way, the four spheres on earth came into existence.
Atmosphere
Biosphere
Hydrosphere
Lithosphere
Fig - 2.1 : Spheres of earth
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Lithosphere :
The part of land on earth on which we live, is known as lithosphere. ‘Litho’ means soil and
‘sphere’ means layer. The upper crust layer of earth is made of soil and solid materials like rock
so it is also known as the solid covering Approximately 29% of the surface of the earth is
covered with lithosphere. This layer is almost 64 km to 100 km thick. Everywhere the layer of
the earth does not possess the same thickness. It does not have same shape either in its interior
or exterior part. It is mostly made up ot substances like soil and rocks. Forms of land like
mountains, plateaus, plains and valleys have developed on lithosphere. The temperature increases
as we move into the interiors of the lithosphere. The melted juice of rocks in the core/interior of
earth is known as magma. There are many gases in the interior of the earth, which on being
heated tries to come out with pressure in upward directions. But the pressure of rocks present
on the surface of earth is equally same. Thus, the balance between the opposite forces like heat
and pressure is maintained. That is why the crust of the earth does not break. When the balance
between the heat and pressure is not maintained in the interiors of the earth the crust of the earth
breaks and volcano erupts. ‘Mummy, How is the lithosphere useful to us ?’
‘If lithosphere is not there then where we can construct our houses ? How will it be possible
to have drinking water, land for agriculture, industries, business, metals, forests etc. without
Lithosphere. So today we have talked about lithosphere only so draw a figure showing what all
can be included in Lithosphere ?’
Activity
Discuss and draw a figure as stated above with the help of your teacher.
Hydrosphere :
‘Now, let me talk to you about Hydrosphere. Some lowered portion of the surface of earth are
filled with water. These parts which are filled with water are known as Hydrosphere. On the
surface of the earth the area of water is more than that of land. Hydrosphere covers 71% of the
earth surface. The portions in the Hydrosphere possessing huge amount of water are oceans.
These oceans are Pacific ocean. Atlantic ocean, Indian ocean and Arctic ocean. All these oceans
are connected with each other. The major water bodies on the surface of earth are seas bays
straits, rivers, lakes etc. The oceans on the earth are huge and deep. Valleys having the depth of 10
to 11 km are located at their bottom. The interiors of oceans like earth are made up of various
forms like high mountains, vast plains, plateaus, valleys etc.
‘Mummy, how much water will there be in the seas ? It is salty. How is it useful to us ?’ Yes,
oceans contain 97% of the total amount of water on the earth. Approximately 1/3 portion of
remaining water is found on the poles and on the Himalayas and other mountains in the form of
snow. Some water is accumulated in the lakes and some flows in the rivers and some is stored in
the interior of earth as ground water. The amount of drinkable water is less. This fresh/sweet
water is the gift of hydrospehere. The sweet water is required by the living beings for their
existence. The main source of this water, which is rain, its moisture comes from the oceans only.
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Valuable chemicals, minerals, salt, fishes etc. is available from the seas. As we have living
world on the earth, in the same way sea has aquactic living world inside it. The magnificient
strength of waves, tides and currents of oceans are used to generate electricity, Beside, these
oceans are also useful as waterways.
Think
If there would have been no seas then ?
Fig - 2.2 : Outline map of world
Activity
Locate using various colours, the location of oceans, seas, bays and traits in the
world map given above.
Now, lets understand the third sphere.
Atmosphere :
‘The covering of the air wrapping the earth from all the four sides is called Atmosphere’. It
extends approximately up tp 1600 km from the surface of earth. It cannot be seen with naked
eyes like Lithosphere and Hydrosphere. Atmosphere is composed of various gases, water vapour
dust particles, meteors, saline particles and micro organisms in it. Atmosphere is colourless,
odourless and transparent. Solid, liquid and gaseous elements are included in the Atmosphere. It
contains approximately 78% nitrogen, 21% oxygen and 1% other gases.
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When we go higher from the surface of earth, the amount of the most of the gases in the
atmosphere decreases. Carbon dioxide gas is heavy so it is more in the lower layer of the air, so
it becomes less as we go up.
Oxygen
Ozone gas is in very proportion in air. This gas absorbs
20.00 the ultraviolet rays from the sun and protectss the earth from
excessive heat of sun. This gas is more in proportion in
%
morning in the open ground and in the air near the sea-coasts.
Gases like oxygen and nitrogen keeps the living creatures on
the earth alive. Nitrogen softens the intensity of oxygen. Water
Nitrogen
is the most important component in the atmosphere. Due to
heat, the water in the form of vapour evaporates and mixes
78.03 %
Other gases
with air which is known as moisture. The process of cooling
0.98 %
of vapour is called condensation. Various forms of moisture
Fig - 2.3 : Amount of gases in atmosphere. like dew, fog, clouds and precipitation are due to condensation
only. The effect of atmosphere is seen on human beings of every region in their food habits,
clothing, habitat, colour, economic activities etc. Many dust particles are seen in the atmosphere.
Sunlight spreads on the earth due to these particles only. Because of this only it does not
suddenly turn dark after sunset and it does not suddenly turn bright after sunrise. The sunrays
are reflected back with the help of these dust particles on the surface of earth and we receive the
light of sun. We are able to listen to the sounds due to the medium of atmosphere. That is why
the radio and doordarshan telecast is possible.
Think
Based on what experiences you can say that atmosphere exists on the surface of
earth ? Make a note of it and disscuss it with your teacher.
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he
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Li
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Fig - 2.4 : Human life and spheres
Now listen, there is existence of fourth sphere that is biosphere on earth due to these three spheres.
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Biosphere :
The part of lithosphere, hydrosphere and atmosphere where the living world is spread is
known as biosphere. Biosphere is one of the important sphere on earth. Earth is the only planet
in the solar system having biosphere. Biosphere includes vegetation, animals, insects and human
beings. We obtain food and many other necessary things from biosphere. We cannot live without
vegetation and animals. Biosphere is the base of our existence and living. It is divided into two
divisions : (1) Non-living and (2) Living. Lithosphere, Hydrosphere and Atmosphere is studied
in the non-living division while plants, animals and micro-organisms are included in the living
world.
Think
Out of the living world staying around us if any one world is destroyed, then what
will be its effect on us ? For example, if birds get destroyed then ? Discuss with your
teacher.
‘If man deteriorates the earth due to its activities, then will there be any effect on these
spheres ?’
Natural
living
components
of atmos
phere
Manmade
Non-living
People
Fig - 2.5 : Components of Atmosphere
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Fig - 2.6 : Effect of human activities on spheres
Human beings knowingly / unknowingly undertake many activites for their self-development.
Due to it the balance of various spheres faces a danger. Like boring the earth too much for the
minerals, atomic research in the interior of earth, too much drilling of earth to find mineral oil
and making tubewells affects the lithosphere and it is in danger. The impurities of villages and
cities along with industrial wastes dumping in the water bodies have made them impure. Due to
increased heat, the snow at polar regions have started to melt. Aquatic creatures are destroyed
due to the waste oil from the ships and deposition of industrial and chemical mixed impurities in
water. The areas having higher mobility of vehicles show increased rate of Carbon Monoxide in
the air. The amount of CO2 in the air increases due to cutting of trees. Heat on the earth
increases due to increase in CO2 in air. In this way, human activities effect the atmosphere.
At the cost of atmosphere exploitation, the nourishing link of nature is put in danger, which
is harmful for biosphere.
Activity
Make a list of natural or man-made events through which big effect has been
seen on the various spheres of earth.
Project
Find out the pollution creating points in your surrounding and study about its
effects and find out possible solutions for it.
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EXERCISES
Q. 1 Answer the following questions :
1.
What do you know about our earth ? Write a short note.
2.
How much time earth would have taken to come in its novel form after being
detached from sun ? Why ?
3.
How are the spheres of earth inter-related ?
Q.2 Fill in the blanks with appropriate words :
1.
There are total ............ spheres on the earth.
2.
Lithosphere covers approximately ........... percent of surface of the earth.
3.
The most important liquid component in the atmosphere is ...................
4.
The portions in the hydrosphere possessing huge amount of water are .................
5.
................. gas absorbs the ultraviolet rays of the sun.
Q.3 Give the meaning of following terms :
(1) Lithosphere (2) Hydrosphere (3) Atmosphere (4) Biosphere (5) Pollution
Q.4 State whether the following statements are true or false :
1.
The earth is a member of solar family.
2.
The water portion on the surface of earth is less than the land portion.
3.
The sweet water is a gift of hydrosphere.
4.
Oxygen softens the intensity of nitrogen.
Q.5 How are given below names related to your life, write it.
1. Mountains
: ...............................................................................................................
2. Fields
: ...............................................................................................................
3. Rivers
: ...............................................................................................................
4. Lakes
: ...............................................................................................................
5. Forest
: ...............................................................................................................
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