Social Science SHORT ANSWER QUESTIONS(3 Mark)

Uses of Rocks:

• Hard rocks are used in making buildings and barrages.
• Houses and buildings are built of rocks (stones, slates, granite, marble).
• Stones are used in numerous games:
• Seven stones (phitthoo).
• Hop scotch (stapu, kit kit).
• Five stones (gitti).
• Rocks (stones and slates) are used in building bridges, embankments.

One type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the rock cycle. Let’s understand it through example-Igneous rocks change into 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 meet down to form molten magma. This molten magma again can cool down and solidify into igneous rocks.

1. Mantle is made of the molten rocks.
2. It is 2900kms deep beneath the crust.
3. The average temperature isn this layer are 2200 degree Celsius.
4. It is made up of denser material.
5. Mantle comprises 84 percent of the earth’s surface.

Igneous rocks are of two types:-

• Extrusive igneous rocks.
• Intrusive igneous rocks.

Sedimentary Rocks:The small particles are called sediments.

• These sediments are transported and deposited by wind, water etc. in low areas.
• These loose sediments are compressed and hardened to form layers of rocks.
• These layered rocks are called sedimentary rocks.

Examples:

• Sandstone.
• These rocks also contain fossils of plants, animals and other micro-organisms that once lived on them.

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The uses of rocks are:-

1. Hard rocks are used for making roads, houses and buildings.
2. Rocks are made of different minerals which are important for mankind; for example, coal, petroleum and natural gas.
3. Rocks like aluminium, gold, uranium, etc. are also used in industries such as medicines, fertilisers, etc.

S.No	Column I		Column II
1.	Granite	(c)	Gneiss
2.	Basalt	(a)	Schist
3.	Coal	(b)	Graphite
4.	Limestone	(d)	Marble

1. The uppermost layer over the earth’s surface is called the crust.
2. It is the thinnest of all the layers.
3. It is about 35km on the continental masses and only 5km on the ocean floors.

Our earth is made up of several concentric layers with one inside another. These layers are three in number- crust, mantle and core.Crust: It is the uppermost layer over the earth's surface. It is the thinnest of all the layers. It is about 35km on the continental masses and only 5km on the ocean floors.
The continental masses are made up of silica and alumina. It is thus called sial (si-silica and al-alumina). The oceanic crust mainly consists of silica and magnesium. It is thus called sima (si-silica and ma-magnesium). Mantle: It is just beneath the crust. It extends up to a depth of 2900km below the crust Core: It is the innermost layer. Its radius is about 3500km. It is mainly made up of nickel and iron and is known as NiFe (ni-nickel and fe-ferrous, Le., iron). The central core has very high temperature and pressure.

When the molten lava comes on earth's surface; it rapidly cools down and become solid. Rocks formed in such a way on the crust are called Extrusive igneous rock. Sometimes molten magma cools down deep inside the earth crust, solid rocks so formed are called Intrusive igneous rocks.

Sometimes the molten magma cools down deep inside the earth’s crust, leading to the formation of solid rocks. These are called intrusive igneous rocks. For example, granite rocks which are used to prepare grinding stone for preparing spice powder.

Igneous rocks are created from the cooling of molten magma/lava. All other rocks are derived from them, which is why you will also find them referred to as parent rocks on occasion. These were the first type of the rocks formed when the earth was formed. The first rocks on Earth were igneous rocks. Igneous rocks are formed by the cooling and hardening of molten material called magma.

The innermost layer of the earth is core with a radius of 3,500km. It is mainly made of nickel and iron and is called nife. (ni-nickel and fe-ferrum, i.e., iron). The central core has a very high temperature and pressure.

The solidified outer crust of the earth is of great importance to us .This thin crust just like the skin of an apple, forms the stage on which human life and civilization have developed. It has the valuable soil and gives us most of our minerals.

One rock changes into another under certain conditions in a cyclic manner.
Molten magma cools down and solidify to form igneous rocks. These rocks are broken down due to pressure and climatic conditions into sediments.
These are transported and deposited to form sedimentary rocks. The igneous and sedimentary rocks under heat and pressure change into metamorphic rocks.
These metamorphic rocks under great heat and pressure melt down to form molten magma. This again cools down to form igneous rocks. This process of transformation of rocks is called 'rock cycle'.

Igneous rocks are formed by cooling of the lava. When the lava cools down on the crust it forms extrusive igneous rock for example basalt. They have grained structure.
Sometimes when it cools down deep inside the crust it forms intrusive igneous rocks. They have large grains for example Granite. Grinding stones are made of granite.

The layered structure of the earth has been known on the basis of variation in temperature, pressure and the density of the material in the interior. The behaviour in the earth quake shock waves travelling from the centre of their origin in all directions has been much helpful to this end.

When the molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a way on the crust are called extrusive igneous rocks. The example is Basalt rock found in Deccan plateau.

Minerals are very important to mankind. Some are used as fuels. Some minerals, such as coal, natural gas and petroleum, iron, aluminium, gold, uranium, etc. are also used in industries. Further they are even used in medicines and in making fertilisers.

The naturally occurring substances which have certain physical properties and definite chemical composition are called minerals, e.g., uranium, gold, coal, natural gas.