Earth – The planet on which we live is called earth.
The earth is a dynamic planet i.e. it undergoes changes constantly. These changes are:
Inside the earth
Outside the earth
Interior of the earth:
The earth is made up of several concentric layers.
Concentric means having a common centre.
The earth has one layer inside another.
Broadly, there are three layers of the earth:
Crust
Mantle
Core
The Crust – The outermost layer over the earth’s surface is called crust.
It is the thinnest of all the layers.
About 35 km on the continental masses and only 5 km on the ocean floors.
The main minerals constituting the continental mass are:
Silica
Alumina
The continental mass is also called ‘sial’. The name sial is derived from letters ‘si’ of Silica and ‘al’ of alumina.
The main mineral constituents of the oceanic crust are:
Silica
Magnesium
The oceanic crust is called ‘sima’. The root of the word sima is ‘si’ from silica and ‘ma’ from magnesium.
Mantle – The layer just beneath the crust and extends up to a depth of 2900 km below the crust are called mantle.
Core – The innermost layer of the earth i.e. it is below the mantle is called core.
Its radius is about 3500 km. The core consists of outer core and inner core.
The temperature and pressure of the central core is very high.
It is mainly made up of: Nickel and Iron
The innermost layer is also called ‘nife’. The name nife is derived from the word ‘ni’ from nickel and ‘fe’ from ferrous meaning iron.
Do you know?
The deepest mine in the world, is in South Africa.
It is about 4 km. deep.
In search for oil engineers have dug a hole about 6 km. deep.
To reach to the centre of the earth (which is not possible!) you will have to dig a hole 6000 km. deep on the ocean floor.
The crust forms only 1 per cent of the volume of the earth, 84 per cent consists of the mantle and 15 per cent makes the core.
The radius of the earth is 6371 km.
Rocks – A natural mass of mineral matter that makes up the earth’s crust are called rock.
The earth’s crust is made up of rocks of various types.
Rocks can be of different: colour, texture, size.
Types of Rocks:
Igneous Rocks
Sedimentary Rocks
Metamorphic Rocks
Igneous rocks – The rocks formed by the solidification on the cooling of molten magma, are called igneous rocks.
The word igneous is derived from the Latin word Ignis which means fire.
Depending on where the molten magma cools, they are of the following types:
Intrusive Rocks
Extrusive Rocks
Intrusive Igneous Rocks – Those rocks are formed by the slowly cooling down of molten magma in deep inside the earth is called intrusive rocks.
When the molten magma cools deep inside the earth’s crust, intrusive igneous rocks are formed.
They Cool down slowly
It formed by Form large grains
Granite is intrusive igneous rock.
Grinding stones used to prepare paste / powder of spices and grains are made of granite.
Extrusive Igneous Rocks – Those rocks are formed by the rapidly cooling down of molten magma on the earth’s surface is called intrusive rocks.
When the molten magma (lava) comes on the earth’s surface, it rapidly cools down and becomes solid.
Rocks formed in such a manner on the crust are called extrusive igneous rocks.
They have a very fine grained structure.
Basalt is an example of extrusive igneous rocks.
The Deccan Plateau is made up of basalt rocks.
Sedimentary Rocks – Those rocks that are formed by the hardening and compression of sediments is called sedimentary rocks.
These rocks get their name from the Latin word sedimentum which means settle down.
These rocks are formed by the settling down of sediments.
These sediments are transported by wind, water etc.
Sandstone is an example of sedimentary rock.
It is made up of grains of sand.
Sedimentary rocks may also contain fossils of plants, animals and other micro – organisms that once lived on them.
Metamorphic rocks – The rocks that are formed when the igneous and sedimentary rocks are subjected to great heat and pressure are called metamorphic rocks.
The Greek word ‘metamorphose’ which means change of form, is the root of the word metamorphic.
These are the rocks that are formed when the igneous and sedimentary rocks change their form under the following two circumstances: Great heat and Great pressure.
The following are the examples of metamorphic rocks:
Slate: Clay becomes slate after metamorphosis.
Marble: Limestone becomes marble after metamorphosis.
Uses of rocks:
Hard rocks are used for making roads, houses, factories, buildings etc.
Red sandstone and marble are used in making buildings.
Many rocks are used as gemstones.
Rock Cycle – The process by which rocks of one kind change into rocks of another kind under certain conditions is called rock cycle.
A cyclic manner is followed in transformation of one type of rock to another type under certain conditions.
Minerals – Naturally occurring substances which have certain physical properties and a definite chemical composition are called minerals.
Rocks are made up of different minerals.
Uses of minerals:
They are used as fuels, for example – coal, petroleum and natural gas.
They are used in industries for making medicines, fertilisers and many other items.
