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HYDROSPHERE

• The earth is called the blue planet. Morethan 71 per cent of the earth is coveredwith water and 29 per cent is with land.

• Hydrosphere consists of water in all itsforms.

• As running water in oceans and riversand in lakes, ice in glaciers, undergroundwater and the water vapour inatmosphere, all comprise thehydrosphere.

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• More than 97% of the Earth’s water isfound in the oceans and is too salty forhuman use.

• A large proportion of the rest of the wateris in the form of ice sheets and glaciers orunder the ground and a very smallpercentage is available as fresh water forhuman use.

• Hence, despite being a ‘blue planet’ weface a shortage of water!!

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Oceans• Oceans are the major part of hydrosphere. They

are all inter connected.• The ocean waters are always moving. The three

chief movements of ocean waters are thewaves, the tides and the ocean currents.

• The five major oceans are the Pacific Ocean, theAtlantic Ocean, the Indian Ocean, the SouthernOcean and the Arctic Ocean, in order of theirsize.

• The Pacific Ocean is the largest ocean. It isspread over one-third of the earth. MarianaTrench, the deepest part of the earth, lies in thePacific Ocean.

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• The Pacific Ocean is almost circular in shape. Asia,Australia, North and South Americas surround it.

• The Atlantic Ocean is the second largest Ocean inthe world.

• It is ‘S’ shaped. It is flanked by the North and SouthAmericas on the western side, and Europe andAfrica on the eastern side.

• The coastline of Atlantic Ocean is highly indented.

• This irregular and indented coastline provides ideallocation for natural harbours and ports.

• From the point of view of commerce, it is thebusiest Ocean.

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• The Indian Ocean is the only ocean named aftera country, that is, India.

• The shape of ocean is almost triangular.• In the north, it is bound by Asia, in the west by

Africa and in the east by Australia.• The Southern Ocean encircles the continent of

Antarctica and extends northward to 60 degreessouth latitude.

• The Arctic Ocean is located within the ArcticCircle and surrounds the North Pole.

• It is connected with the Pacific Ocean by anarrow stretch of shallow water known asBerring strait. It is bound by northern coasts ofNorth America and Eurasia.

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ATMOSPHERE• The earth is surrounded by a layer of gas called the

atmosphere.

• This thin blanket of air is an integral and importantaspect of the planet. It provides us with the air webreathe and protects us from the harmful effects ofsun’s rays.

• The atmosphere extends up to a height of about1,600 kilometres.

• The atmosphere is divided into five layers based oncomposition, temperature and other properties.

• These layers starting from earth’s surface are calledthe troposphere, the stratosphere, the mesosphere,the thermosphere and the exosphere.

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• The atmosphere is composed mainly ofnitrogen and oxygen, which make up about 99per cent of clean, dry air.

• Nitrogen 78 per cent, oxygen 21 per cent andother gases like carbon dioxide, argon andothers comprise 1 per cent by volume.

• Oxygen is the breath of life while nitrogen helpsin the growth of living organisms.

• Carbon dioxide, though present in minuteamount, is important as it absorbs heat radiatedby the earth, thereby keeping the planet warm.

• It is also essential for the growth of plants.10/13/2020 9

• The density of the atmosphere varies with height. It ismaximum at the sea level and decreases rapidly as wego up.

• The climbers experience problems in breathing due tothis decrease in the density of air. They have to carrywith them oxygen cylinders to be able to breathe at highaltitudes.

• The temperature also decreases as we go upwards. Theatmosphere exerts pressure on the earth. This variesfrom place to place.

• Some areas experience high pressure and some areaslow pressure. Air moves from high pressure to lowpressure.

• Moving air is known as wind.10/13/2020 10

BIOSPHERE – THE DOMAIN OF LIFE

• The biosphere is the narrow zone of contactbetween the land, water and air.

• It is in this zone that life, that is unique to thisplanet, exists.

• There are several species of organisms thatvary in size from microbes and bacteria tohuge mammals.

• All the living organisms including humans arelinked to each other and to the biosphere forsurvival.

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• The organisms in the biosphere may broadlybe divided into the plant kingdom and theanimal kingdom.

• The three domains of the earth interact witheach other and affect each other in some wayor the other.

• For example, cutting of forests for fulfilling ourneeds of wood, or clearing land for agriculturemay lead to fast removal of soil from slopes.

• Similarly earth’s surface may be changed dueto natural calamities like earthquakes.

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• For example, there could be submergence ofland, as happened in the case of Tsunamirecently.

• Parts of Andaman & Nicobar islands weresubmerged under water. Discharge of wastematerial into lakes and rivers makes the waterunsuitable for human use.

• It also damages other forms of life.

• Emission from industries, thermal powerplants and vehicles, pollute the air. Carbondioxide (CO2) is an important constituent ofair

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• But increase in the amount of CO2 leads toincrease in global temperatures.

• This is termed as global warming.

• There is thus, a need to limit the use ofresources of the earth to maintain the balanceof nature between the domains of thelithosphere, the atmosphere and thehydrosphere.

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