GEOGRAPHY (VII)-LESSON-2 INSIDE OUR EARTH (LESSON NOTES)

GEOGRAPHY (VII)-LESSON-2

INSIDE OUR EARTH

(LESSON NOTES)

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v INTRODUCTION

Ø The earth, our homeland is a dynamic planet. It is constantly undergoing changes inside and outside. The radius of the earth is 6371 km. In this lesson we will try to know the interior of the Earth.

v INTERIOR OF THE EARTH

Ø The earth is made up of several concentric layers with one inside another. Three most important are these-

Ø 1. CRUST-The uppermost layer over the earth’s surface is called the crust. It is the thinnest of all the layers. The crust forms only 0.5 per cent of the volume of the earth. It can be divided into these two types.

INTERIOR OF THE EARTH AND CRUST

§  Oceanic Crust-The top layer of crust in the oceans are called as oceanic crust. The depth of oceanic crust is only 5 km. The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)

§  Continental crust:- The top layer of crust on the continents are called as continental crust. The depth of continental is nearly 35 km. The main mineral constituents of the continental mass are silica and alumina. It is thus called sial (si-silica and al-alumina).

Ø 2. Mantle- The second layer below the crust is called as mantle. It extends up to a depth of 2900 KM. The mantle forms 16 per cent of the volume of the earth. Nearly 2900 KM the temperature is very high and mostly things are in liquid form.

Ø 3. Core- The innermost layer of the earth is known as core. Its radius is about 3500 km and makes 83% of the volume of the Earth.It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron). The central core has very high temperature and pressure.

v ROCKS

Ø Any natural mass of mineral matter that makes up the earth’s crust is called a rocks. Rocks can be of different colour, size and texture.There are three major types of rocks:

Ø  Igneous rocks- The rocks which is formed by cooling down of molten magma are called as igneous rocks. They are called as primary rocks. There are two types of igneous rocks:

§  Intrusive Igneous rocks- The rocks formed when the molten magma cool down in the interior of the earth  and become solid are called as Intrusive Igneous rocks. For example- Granite.

§  Extrusive Igneous rocks- When the molten magma come out from the interior of the earth and become soled on the on its surface. Such formations of rocks are called as extrusive igneous rocks. For example Basalt. Deccan plateau is made up of Basalt.

Ø Sedimentary rocks – The rocks which are made up of sediments are called as sedimentary rocks. These sediments are the small particles of rocks which formed due to heat, crack down and transported by wind and water. After some years these sediments become compress and become soled and form the sedimentary rocks. These rocks may also contain fossils of plants, animals and other microorganisms. For example- sandstone is made from grains of sand.

Ø Metamorphic rocks.  Due to heat and pressure the igneous and sedimentary rocks can change its forms that are known as metamorphic rocks. For example, clay changes into slate and limestone into marble.

v IMPORTANCE OF ROCKS

Ø The hard rocks are used for making roads, houses and buildings.

Ø The rocks are also used in many games as. For example, seven stones (pitthoo), hopscotch (stapu/kit kit), five stones (gitti).

Ø In the rocks many minerals are also found as coal, iron, gold etc.

v MINERALS

Ø Naturally occurring substances which have certain physical properties and definite chemical composition are called as minerals.

Ø IMPORTANCE OF MINERALS-

§  Minerals are very important to humankind.

§  Some are used as fuels. For example-  coal, natural gas and petroleum,  uranium

§  They are also used in industries – iron, steel, aluminum, copper etc.

§  Minerals are used to make jewelry. For example- gold, silver, diamond etc.

§  Minerals are used to in medicine and to make fertilisers.

v ROCK CYCLE

Ø The process of transformation of the rock from one to another is known as the rock cycle.

ROCK CYCLE

Ø As you know that primary rock or igneous rocks are formed by molten magma.

Ø After that these rocks broken down into small pieces and by deposition of these sediments the sedimentary rocks are formed.      

Ø After that due to heat and pressure these sedimentary rocks changed into metamorphic rocks.

Ø The metamorphic rocks which are still under great heat and pressure melt down to form molten magma. So this process continued.

v GLOSSORY

Ø Fossils: The remains of the dead plants and animals trapped in the layers of rocks are called fossils

Ø The Red Fort is made of red sandstone The Taj Mahal is made of white marble.

Ø To reach to the center of the earth (which is not possible!) you will have to dig a hole 6371 km. deep on the ocean floor

Ø The deepest mine in the world, is in South Africa. It is about 4 km.