Important General Knowledge Notes For All Competitive Exams: Geography - Part-01


Earth's Interior:The huge size of the earth and increasing temperature with depth has set a limit to
direct observation of the earth’s interior.

Structure Of The Earth's Interior:
  • Core, mantle and crust are the three main concentric layers of the earth’s interior.
  • Core is the innermost layer and has the highest density. It is made up mainly of nickel and iron.
  • Mantle is the layer lying between the core and lithosphere. Its major constituents are silicon and magnesium.
  • Crust is the outermost layer of the earth and is mainly composed of silicon and aluminium.
 Temperature, Pressure And Density Of The Earth's Interior:
  • In the upper 100 km, the increase in temperature is at the rate of 12°C per km, in the next 300 km it is 20°C per km but is only 100C per km below it.
  • Thus the rate of increase of temperature beneath the surface decreases towards the centre. 
  • The temperature at the centre is estimated to lie somewhere between 3000°C and 50000C.
  • Such a high temperature inside the earth may be due to chemical reactions under high pressure conditions and disintegration of radio active elements.
  • The pressure also increases from the surface towards the centre of the earth due to huge weight of the overlying rocks. 
  • Therefore in deeper portions, the pressure is tremendously high. 
  • The pressure near the centre is considered to be 3 to 4 million times the pressure of atmosphere at sea level.
Due to increase in pressure and pres ence of heavier materials towards the earth’s centers, the density of earth’s layers also goes on increasing.

Materials Of The Earth's Crust:
  • The outermost part of lithosphere is called crust. 
  • This is the most significant part of the earth because it is occupied by humans. 
  • Crust is made up of more than 2000 minerals, but out of these, 6 are the most abundant and contribute the maximum to this uppermost part of the earth. 
  • These are feldspar,quartz, pyroxenes, amphiboles, mica and olivine.
  • The material of the crust is made up of rocks. The rocks are of different types.
 Types Of Rocks:
Rocks differ in their properties, size of particles and mode of formation. On the basis of mode of formation rocks may be grouped into three types:
  • Igneous rocks are formed by the solidification of hot molten material called magma or lava.
  • Extrusive igneous rocks are formed by cooling of lava on the earth’s surface e.g. basalt, gabbro. 
  • Instrusive igneous rocks are for med by solidification of magma below the earth’s surface, e.g. granite. The huge blocks of coarse granitic rocks are found both in the Himalaya and the Decean Plateau.
  • Sedimentary rocks are formed by the successive deposition of sediments.
  • These rocks have layered structure, there fore they are also known as stratified rocks.
  • Fossil is the solid part or an impression of a prehistoric animal or plant embedded in sedimentary rocks in which they are buried.
  • Gypsum, rock salt and nitre are examples of such sedimentary rocks.  
  • Huge folded mountains of the world like Himalayas, Andes etc. are made up of sedimentary rocks. All the alluvial deposits of the world are also due to sedimentary accumulations. 
  • All river basins, particularly their plains and deltas, e.g. Indo- Gangetic plain and Ganga-Brahmaputra delta are good examples of sedimentary accumulations.
3. Metamorphic:
  • Metamorphic rocks are formed by the effect of heat or pressure on sedimentary or igneous or even metamorphic rocks.
  • Thermal metamorphism is the process by which a rock under-goes change as a result of great heat.
  • Dynamic metamorphism is the modification of rock, by tremendous pressure during extensive earth movements.
  • In India, marble is found in Rajasthan, Bihar and Madhya Pradesh, whereas slates are available in plenty in Orissa, Andhra Pradesh and Haryana. In Kangra and Kumaun regions of Himalaya, slates of different colours are found. 

Name Of The Rock
Type Of Rock
Name Of The Metamorphic Rock
Rock Marble
Rock Marble
Rock Quartzite
Rock Slate
Rock Phylite/Schist
Rock Graphite / Diamond
Rock Gneiss
Rock Schist

Weathering And Its Types:
Weathering: Weathering is the process by which exposed rocks are disintegrated and decomposed in situ (i.e their original position).

Types Of Weathering:
We can recognize three types of weathering as follows:

1. Physical Weathering: 
  • When the rocks are broken up into smaller fragments without any chemical change in their composition, it is called physical weathering.
  • The term mechanical weathering is also used for physical weathering.
  • The rapid heating and cooling of the rocks creates a series of joints and cracks which lends to breaking up into smaller blocks. This process is known as block disintegration.
  • A weathering process by which the outer layers of the rock peel out in concentric cells due to difference of temperature in the outer layers is called exfoliation.
  • Breaking up of rocks due to freezing of water in the rock joints and cracks, in very cold regions, is called frost action.
 2. Chemcial weathering: 
  • Decomposition of rocks by chemical processes with the help of water and atmospheric gases is called chemical weathering.
  • Chemical weathering involves the process of oxidation, carbonation, hydration- and solution.
 3. Biotic weathering: 
  • Biotic weathering is carried out by plants, animals and man.
  • Biotic agents like plants, animals and man also contribute to physical and chemical weathering.
  • Exogenetic forces are constantly working to bring about leveling or the gradation of land. 
  • They attempt to achieve a condition of balance between erosion and deposition which mean a graded position. These forces operate through the process called the process of gradation. 
  • Agents of gradation like rivers, glaciers winds, sea waves and underground water perform their task with the help of the triple action of weathering, erosion and deposition. 
  • The leveling down of elevated portions of the earth’s surface is done by erosion.
  • Levelling and smoothening of land surface is called gradation includes both degradation and aggradation.
Components Of Gradation:
The work of gradation has two components:
1. Degradation: The weathering of the land surface by erosion is called degradation.
2. Aggradation:  Raising or filling up of depressions by deposition is called aggradation.

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