Chapter 5
Water Surrounding the Earth
We have read in the
previous chapter that planet earth is often called the Water planet or the Blue
planet because of the presence of abundant water on it. Water covers about 71 per cent of the earth's
surface and is present as oceans, rivers, lakes, underground flow, glacial ice
and water vapour in the air. More than
97 per cent of this realm of water on the earth is salt water present in oceans
and seas, about 2 per cent is glacier ice and less than 1 per cent of all the
water on earth is fresh water in rivers and lakes. Thus, the oceans namely Pacific, Atlantic,
Indian and Arctic are the largest reservoirs of water on our earth. Let us study about these principal water
bodies, their nature, source, movement and importance in our life. The earth receives major part of pure water
through rainfall. In addition, it
receives fresh water through numerous springs and rivers. The water never remains static, it has a
cycle which has neither a beginning nor an end.
Let us find out in detail, how the process of water cycle works. THE PROCESS OF WATER CYCLE Condensation for
Clouds Conden Wat storage adve change transport and now treated
Evapotranspiration Evaporation Occa An Process of Water Cycle The sun is the
main source of energy which causes water to evaporate. Hence, water of the oceans is converted into
water vapors due to the heat of the sun by the process of evaporation. 33
Unable to float, they fall down over the earth's surface as
precipitation. It is because of this new
The evaporated vapors rise up in the atmosphere and condense into tiny crystals
of ice or drople of water to form clouds.
When the condensed ice crystals or water droplets grow in size and a
ending circulation that the process is described as water cycle. A major part of the water runs off over the
earth's surface forming numerous streams.
A sm = part of rain water percolates (seeps) inside the earth which
forms ground water. The ground wate is a
very important source of water for plants.
The plants derive the ground water through their face system and return
it to the atmosphere in the form of moist air through their leaves. Water is als present in the form of ice -
crystals in high altitude regions. Thus,
we can infer that there is a continuous supply of water to our earth. However, the distribution of water is not
uniform. Some areas receive heavy
rainfall or snowfall which increases water supp and makes it surplus
there. On the other hand, areas
receiving low rainfal or snowfall have scarcity of water. We can regulate this resource by storing the
surplus water in large reservoirs or by conserving it in several other
ways. To sustain life on the earth, the
judicious use of water is necessary. So,
we should Water Reservoirs save this precious natural resource. VARIOUS MOVEMENTS OF OCEAN WATER When we
throw a pebble in a river or a pond, we observe ripples in the water. Like, on the sea coasts, we can observe the
rolling waves of the sea water. What
causes their movement and from where do these ripples originate? Let us study about these movements. These movements in ocean waters are basically
of three kinds, i.e. waves, ocean
currents and tides. Let us discuss them
in detail. AHAL Waves The waves are the
movements in a water body where water particles move up and down. It is important to note that water actually
does not travel with the wave. This is
like a ball thrown in the water. The
ball keeps on moving up and down along the wave. This rhythmic movement of water particles
produces a pattern, which we can see as waves.
The height of waves depends on the speed of wind and sea waves 34)
the duration of wind blowing from a particular direction
Together, it determines the size of a wave.
Do you know? Ocean currents The
ocean current is the continuous movement of a now a days, energy of waves is
mass of water in a particular direction.
Ocean currents are harnessed to produce electricity broadly of two
types, i.e. cold currents and warm
currents. These are formed due to
heating and cooling of the ocean water.
We know that cold water is denser than the warm water. Due to the higher density of cold water, it
sinks down below the warm water. Thus,
the cold water of the polar region moves slowly towards the equator along the
bottom of the ocean. The warm water near
the equator moves along the surface of the ocean towards the poles. In this manner, ocean currents are
caused. In the given map, you can
observe the distribution of some major ocean currents in the world. These currents tend to move towards the right
in the Northern Hemisphere and towards the left in the Southern Hemisphere. Generally, warm currents flow along the east
coast of the continents while cold currents flow along the west coast of the
continents. Oren Ini Oya NA NN Pace
California Kurse Canary GUS N. Equatorial Equatorial Court N. Equatorial
Equatorial Counter Meloung Egural Equatorial Counter 3. Equatorial NE E Court
Equatorta Dengue W. Australia be E Am 3. Pacite Antarctic Circular 3. Atlantic
Antareti Circumpol Antarete Supoiler 3.
Indian Antarctic Circular Antanete Major Ocean Currents The ocean currents play
an important role in influencing the climate of the coastal regions of the
continents. If a warm current passes
along the coast, it raises temperature and makes the place warmer than the
surrounding areas. Similarly, cold currents
make the adjoining coastal region colder.
In coastal areas, warm ocean currents cause rainfall and therefore,
influence its climate, making it warm and moist. The cold currents, on the other hand, tend to
make the climate cool and dry. Thus,
these oceanic currents modify the climate in the coastal regions. Another interesting characteristic is that
the confluence of warm and cold currents provides ideal conditions for
plentiful growth of plankton, which is a food for the marine life. These areas serve as major fishing grounds,
encouraging trade and commerce. The
ocean currents also help in navigation 35
Tides Tides are the periodic rise and fall in the level of
ocean water. They are caused due to the
gravitational pull of the moon and the sun.
Tides occur twice a day. When the
level of water rises, it is a high tide and when the level falls, it is a low
tide. Sometimes, high tide enables big
ships to enter the Do You Know? Harbor
or sail out of the Harbor Kolkata Port in India is an example of the time
interval between a high tide and a low tide 1.
tidal port. Now a days, tidal
energy is 6 hours 13 minutes. is
harnessed to generate electricity in Haji Ali Dargah, located in Arabian sea,
in Mumbai is the live example of high and low tide. One can visit the coastal areas. Tidal energy is one of the important
renewable sources of the Dargah only when it is low tide. energy.
IMPORTANCE OF OCEANS TO MAN The oceans facilitated countries and regions
to trade with one another. Goods can be
moved in a very large quantity by ships and the transportation is cheaper than
any other mode of transport The marine environment provides animal and plant
life for food and trade in abundance.
The oceans, thus, are a valuable source of food. Some of the valuable mineral resources are
also found in the ocean floor. Mineral
oil, manganese nodules, gold, platinum, nickel, copper and cobalt are some of
the valuable minerals found in different parts of the oceans. Several countries are tapping mineral oil as
a source of energy in a big way.
However, the exploitation of the deep ocean floor as a source of
minerals is still at an early stage. in
future, it is hoped that the oceans will serve as a major source of valuable
oil rig of ONGC, Mumbai resources. CASE
STUDY OF TSUNAMI In December 2004, gigantic waves, the likes of which were never
seen before, crashed into the coastal areas in many parts of the world, washing
away people, animals and homes. There
were unprecedented losses, and the whole world watched in horror 36)
Government agencies,
Non Governmental Organizations (NGOs), Resident Welfare Associations, business
organizations, shopkeepers, schools and colleges provided relief to the victims
by donating money, clothes, medicines, beddings, tents, etc.: Media played an
important role in mobilizing public help
for the victims. Do you
know? Huge sea waves are called Tsunami
which is a Japanese name. These waves
are caused by the earthquake, under water volcanic eruption or any other such
severe disturbance. High waves during
Tsunami INDIA 15,000 BANGLADESH 21 MYANMAR 61 THAILAND 400 SRI LANKA 21.0067
ALA MALATSIA MALDIVES 62 dead Epicentre 9.3.
magnitude quake SUMATICA NU OCE INDONESIA 168,000 EAST AFRICA atorg 94
Areas affected by Tsunami Havoc caused by Tsunami Keywords fishing grounds an area
in the oceans and seas where fish are in plenty and fishing is usually good,
plankton: microscopic organisms that drift in the upper water of the sea.
Most marine creatures depend upon them directly or indirectly for
food. Plankton rich zones in the ocean
make good fishing grounds. stream flow:
a portion of run off that enters the river valleys to move towards the
oceans. surface run off the part of
total precipitation that flows over the ground.
transpiration: the transfer of water vapour to the air from plants. . 37
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