Class7 Inside our earth

Inside our earth:-

Introduction:-

• The earth is a dynamic planet.
• It is constantly undergoing changes inside and outside.

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:-

• Any natural mass of mineral matter that make up the earth crust is called rock.
• It can be of different colours, size and texture.
• Types of rocks:- three types
• Igneous rocks, Sedimentary rocks and metamorphic rocks.

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.