Cbse guide: What are the main constituents of the core? What are called igneous rocks? What are fossils? What happens when igneous and sedimentary rocks go under great heat and pressure?

Inside our earth:-

Introduction:-

Interior of the earth:-

The earth is made up of several concentric layers with one inside another.
Crust:- The uppermost layer over the earth's surface is called crust.
It is thinnest of all the layers
It is about 35 Km on the continental masses and only 5 Km on the ocean floor.
The main mineral constituents of continental mass are silica and alumina (sial).
The oceanic crust mainly consists of silica and. Magnesium (Sima)
Mantle:-Just beneath the crust is the mantle.
It extends upto the depth of 2900 Km below the crust.
Core:- Innermost layer with a radius of about 3500 Km
Mainly made up of nickel and iron (nife , Fe= ferrous means iron).
Central core has very high temperature and pressure.

Rocks and minerals:-

Igneous rocks:-

Also called primary rocks.
When the molten magma cools, it becomes solid.
Rocks thus formed is called igneous rocks.
It is of two types:-
Intrusive rocks,
Extrusive rocks.
Extrusive igneous rocks:-
Lava is actually fiery red molten magma coming out from the interior of the earth on its surface
When this molten lava comes on the surface of the earth, it rapidly cools down and become solid.
The rocks formed in such a way on the crust is called Extrusive igneous rocks
They have very fine grained structures.
Example:-basalts.
Deccan plateau is made up of basalt rocks.
Intrusive igneous rocks:-
Sometimes the molten magma cools down deep inside the earth crust
Solid rocks so formed is called intrusive igneous rocks.
Since they cools down slowly they forms large grains.
Example:- Granite.
Grinding stones used to prepare paste/powder of spices and grains are made up of granite.

Sedimentary rocks:-

Rocks roll down, cracks and hit each other and are broken down into small fragments.
These small particles are called segments
These segments are transported and deposited by wind, water etc.
These loose segments are Compressed and harden to forms layers of rocks.
These types of rocks are called sedimentary rocks.
For example:- sand stones is made from grains of sands.
These rocks also contains fossils of plants, animals and other micro-organism that once lived on them.

Metamorphic rocks:-

Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure
For example:-
Clay changes to slate
Limestone changes to marble.

Importance of rocks:-

Rocks are very useful to us.
Hard rocks are used to make roads, houses and building.
Rocks are used in many games such as seven stones (pitthoo), hopscotch(stapu), five stones (gitti)

Rock cycle:-

One type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of rock from one to another is called rock cycle.
When the molten magma cools, it solidify to becomes igneous rocks.
These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks
When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks
The metamorphic rocks which are still under great heat and pressure melt down to form molten magma.
The molten magma again cools down and again cools down and solidify into igneous rocks.

Rocks are made up of minerals.

Minerals are naturally occurring substances which have certain physical propertiesand definite chemical composition.
Minerals are very important to man- kind.
For example:- coal, petroleum and natural gas are used as fuel.
Iron, aluminium, uranium, gold etc are used in industries, in medicine and in fertilizers etc.

More to know:-

The deepest mine in the world is in South Africa. It is about 4 Km deep .
In search of oil engineers have dug a hole about 6 Km deep.
To reach to the centre of earth , we have to dig a hole about 6000Km deep on the ocean floor.
The crust forms only 1% of the volume of earth, 84% consists of mantle and 15% make core.
The radius of earth is 6371Km.
Latin words :- igneous = fire; sedimentary= settle down; metamorphic= change of form.
Fossils:- The remains of dead plants and animals trapped in the layer of rocks is called fossils.

Cbse guide