Lithosphere, Rocks, Soil, Mountains, Denudation, the Atmosphere, the Oceans

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The Lithosphere

The mass of the Earth is generally divided into three layers, namely, Crust, Mantle and Core. The Lithosphere is the name given to the outer Crust which is not more than 10 miles thick. It is made up of a great variety of rocks, soils, etc.


Sedimentary Rocks

  • These rocks are made up of deposits laid down on the floor of river beds, lakes and seas.
  • Examples: Sand and sandstone, clay, lime stone, chalk and carbonaceous rocks, such as lignite, coal and anthracite.

Igneous Rocks

  • These are primary rocks which are formed by cooling and solidification of molten lava.
  • When such rocks are poured out on the surface they are known as volcanic rocks, e. g. basalt.
  • When the molten material solidifies at considerable depth, plutonic rocks are formed, e. g. Granite.

Metamorphic Rocks

These rocks are formed as a result of alteration by extreme heat and or pressure of igneous or sedimentary rocks. Example, slate, gneiss, schist etc.


  • The upper layers of rocks weather to form the soil. There are three distinct layers of soil. The uppermost layer forms the top soil. The second layer is called the subsoil. The third layer is made up of decomposing and much-broken rock, known as mantle- rock.
  • The type of soil depends on a number of factors, namely, climatic conditions, the nature of the parent rock, relief, vegetation and the period over which it has been worked by man. Soils may by broadly classify as (a) Forest, (b) Grassland and (c) Desert types.


  • In past geological ages disturbances in the Earth՚s interior have caused crumpling and cracking of the crust. This has resulted in great upholds forming Fold- Mountains which are mainly made up of folded strata of sedimentary rocks, e. g. the Alps, the Rockies, the Andes, and the Himalayas. The mountain structures worn down by prolonged denudation are known as Residual Mountains, e. g. Highlands of Scotland and Scandinavia.


  • The process known as denudation or the wearing away of the land is continually going on. The chief causes of such erosion are
    • Changes in temperature;
    • Frost;
    • Winds;
    • Water, including rivers;
    • Ice; and
    • The action of the sea.
  • Steps to combat soil erosion include (i) terracing; (ii) contour ploughing; (iii) strip cropping (iv) planting shelter belts of trees; and (v) plugging the gullies by building small dams etc.

The Atmosphere

  • The air is composed mainly of nitrogen (78 %) and oxygen (21 %) with small proportions of carbon dioxide, water vapour and rarer gases like argon and neon. Atmosphere is 200 miles thick, but nine-tenths of the air composing it is found within 12 miles, and half within 3 miles of the earth՚s surface. We are concerned mainly with the lower layer of troposphere. The upper layers in the ascending order are Stratosphere, Mesosphere and Ionosphere.
  • Troposphere extends to a distance of about ten kilometres. Stratosphere is a region extending from an altitude of about 11 Km to 50 Km above the earth. The upper part of stratosphere has plenty of ozone which protects us from the fatal effects of Sun՚s ultraviolet radiation.
  • Mesosphere is the next layer extending from 50 to 80 Kms above the earth. It is a very cold region. Ionosphere extends from about 60 Kms upwards. It includes Thermosphere and Exosphere which marks the outer limits of the earth՚s atmosphere.

Wind is Air in Motion

  • The chief cause of wind is difference in atmosphere pressure. One of the main reasons for differences in pressure is unequal heating of the air. From the high pressure belts the air flows outwards to the regions of low pressure. Owing to the rotation of the earth, the winds do not blow due north and south, but are deflected. In this deflection they obey Ferrell՚s Law which states, “Any moving body on the earth surface including a current of air tends to be deflected, the deflection being to the right in the northern hemisphere and to the left in southern hemisphere.”
  • Land and sea breezed are local winds caused by the unequal heating of land and water. During the day the land becomes very much hotter than the sea, with the result that there is marked low pressure over the land. Thus the air over the sea flows rapidly loses heat, but the sea remains warm for a longer time. Thus at night, heavy cool air blows from the land to take the place of warm air rising over the sea. The monsoon or seasonal winds may be regarded as land and sea breezes on a large scale, in which the time-frame is a year instead of a day.
  • This phenomenon is to be found in south-east Asia, but is especially marked in the subcontinent of India. A cyclone is a portion of the atmosphere in which the pressure is lowest in the centre. The winds blow inwards in anti- clockwise direction in the Northern Hemisphere. In the Southern Hemisphere cyclonic winds blow in a clockwise direction in accordance with Ferrell՚s Law.
  • An anticyclone is a portion of the atmosphere in which the pressure is highest in the centre. The winds blow outwards in a clockwise direction in the Northern Hemisphere and in an anti-clockwise direction in the Southern Hemisphere.

The Oceans

  • It is estimated that 72 % of the surface of the globe is covered with water. The Pacific, which is the greatest of all oceans, covers a third of the earth՚s surface, its total area being greater than that of all the dry land. Atlantic are slightly less than half the size of the Pacific, yet so many great rivers flow into it that it receives half the drainage of the world.
  • The other oceans are Indian, Mediterranean, Antarctic and Arctic. The average depth of the ocean is 12,500 feet, compared with the average height of the land which is about 2,500 feet. The greatest known depth is that of the Marianas Trench in the Pacific, where a depth of 35,800 feet has been recorded.

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