Q 1 – Why is the earth called a dynamic planet?
Ans – The earth is called a dynamic planet because movements, forces etc., constantly act inside and outside the earth.
Q 2 – Name the uppermost layer of earth.
Ans – The uppermost layer of earth is called the crust.
Q 3 – Into how many types of the layers of the earth is divided?
Ans – The earth consists of three layers:
1. Core (inner core and outer core)
2. Mantle (upper and lower mantle)
3. Crust (continental and oceanic crust)
Q 4 – What do you understand about the uppermost layer of the earth? Briefly describe.
Ans – The uppermost layer over the earth’s surface is called the crust. It is the thinnest layer and its depth is about 40km, and its range is about 35km on the continental masses and only 5 km, on the ocean floors.
Q 5 – What is lava?
Ans – Lava is the hot red magma coming out from the interior of the earth to the surface. It cools down and become solid.
Q 6 – How is a sedimentary rock made?
Ans – Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called sediments. These sediments form sedimentary rocks.
Q 7 – What are extrusive igneous rocks? Give an example.
Ans – 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. They have a very fine-grained structure. The Deccan plateau is an example that is made up of basalt rocks.
Q 8 – What is earth’s crust made up of?
Ans – Earth’s crust is made up of a different types of rocks. Rock is a natural mass of mineral matter. It is of different sizes, colours and textures and shapes. Earth is made up of sedimentary, igneous or metamorphic rocks.
Q 9 – Describe the Rock cycle.
Ans – In a cyclic manner one type of rock changes into another type. As we already learnt when the molten magma cools, it solidifies to become igneous rock. 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 under great heat and pressure meltdown and form molten magma. This molten magma again can cool down and solidify into igneous rocks.
The Rock cycle can be understood and expressed by cycle as shown below:
Q 10 – How is the earth a dynamic planet?
Ans –
- The earth is our homeland.
- It is a dynamic planet.
- It is constantly undergoing changes inside and outside.
- Interior of the Earth.
Q 11 – What is the importance of the outer crust to us?
Ans – 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 valuable soil and gives us most of our minerals.
Q 12 – Draw a structure of the interior of the earth
Ans –
Q 13 – Have you ever wondered what lies in the interior of the earth? What is the earth made up of?
Ans – Yes.
The interior has three major layers of rocks of different densities.
The earth is made up of rocks
Q 14 – Describe the interior of the earth
Ans – Interior of the Earth:
The earth is made up of several concentric layers with one inside another, just like an onion.
Crust:
The uppermost layer on the earth’s surface is called the crust.
It is the thinnest of all the layers.
It is about 35 km, thick on the continental masses and only 5 km thick on the ocean floors.
Main minerals constituent of the continental mass are silica and alumina.
It is thus called sial (si – silica and al – alumina).
Mantle
Just beneath the crust is the mantle.
It extends up to a depth of 2900 km below the crust.
Core
The innermost layer is the core with a radius of about 3500 km.
It is mainly made up of nickel and iron.
Hence it is called nife (ni—nickel and fe—ferrous i.e., iron).
The central core has very high temperature and pressure.
Q 15 – Describe igneous rocks.
Ans – Igneous Rocks
The molten rock material is called magma.
When it cools, it becomes solid.
Rocks formed in this way are called igneous rocks.
They are also called primary rocks because other rocks are formed out of these rocks
There are two types of igneous rocks.
Intrusive Rocks and Extrusive Rocks
Formation of Extrusive and Intrusive Rocks:
Due to extreme heat in the interior of the earth, rocks are found in the form of molten material called magma.
When magma comes out on the surface of the earth, it cools down and turns into solid rocks. Such rocks are termed as extrusive rocks.
Examples: Basalt.
Deccan Trap is built of basalt.
When the molten magma cools down within the interior of the earth, it becomes solid to form intrusive rocks
Examples: Granite and Garbo
Q 16 – What are the two types of Igneous rocks?
Ans – Igneous rocks are formed by the cooling of the lava. When the lava cools down on the crust it forms extrusive igneous rock for example basalt. They have a 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
Q 17 – How are extrusive and intrusive rocks formed?
Ans – Intrusive and extrusive rocks are types of igneous rocks which are formed when magma cools down and solidifies.
• Extrusive rocks: When the molten magma 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. They have a very fine structure. For example, basalt.
• Intrusive rocks: Sometimes the molten magma cools down deep inside the earth’s crust or surface. Solid rocks so formed are
called intrusive igneous rocks. Since they cool down slowly, they form large grains. For example, granite.
Q 18 – Define the term sediment
Ans – Rocks due to cracks and hitting, breakdown into smaller fragments called sediments
Q 19 – Give an account of sedimentary rocks.
Ans – 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.
Q 20 – What are Fossils?
Ans – Fossils: The remains of dead plants and animals trapped in the layers of rocks are known as fossils.
Q 21 – What are metamorphic rocks?
Ans – Metamorphic rocks are actually igneous or sedimentary rocks that changed due to great heat and pressure. Small crystals combine together to form large crystals. The act of metamorphism takes hundreds of years. Examples—clay changes into slate
and limestone changes into marble.
Q 22 – How are metamorphic rocks formed?
Ans – Igneous and Sedimentary rocks change into metamorphic rocks under heat and pressure
Metamorphic Rocks:
When under heat and pressure igneous rocks and sedimentary rocks change their form and more precious
rocks are formed to be known as metamorphic rocks.
Examples:
- Granite into granite gneiss.
- Coal into slate.
- Slate into schist.
- Limestone into marble.
Limestone is changed into marble due to the following reasons:
The overlying layers of rocks put pressure on the underlying rocks.
From surface to interior of the earth, temperature and heat go on increasing.
Due to pressure and heat, the original limestone changes into marble.
Q 23 – What is mantle?
Ans – It is an intermediate layer that lies between the crust and the core of the earth. Its avg thickness is about 29,00 km. It is believed to consist of solid ultrabasic rocks, rich in iron and magnesium.
Q 24 – What are the uses of rocks?
Ans – 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..
Q 25 – Briefly describe the ‘rock cycle’
Ans – One rock changes into another under certain conditions in a cyclic manner.
Molten magma cools down and solidifies 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 meltdown to form molten magma. This again cools down to form igneous rocks. This process of transformation of rocks is called the ‘rock cycle’
Q 26 – What is the source of knowledge of the layered structure of the earth?
Ans – 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 earthquake shock waves travelling from the centre of their origin in all directions has been much help to this end.
Q 27 – What are minerals? How are minerals important to us?
Ans – Minerals:
Rocks are made up of different minerals.
Minerals are naturally occurring substances which have certain physical properties and definite
chemical compositions.
Minerals are very important to us.
Some are used as fuels.
Examples: Coal.
Natural gas.
Petroleum.
They are also used in industries as energy and raw material.
Examples:
Iron.
Aluminium.
Gold.
Uranium
They are used in medicine, in fertilisers etc..
Q 28 – Distinguish between crust and core.
Ans –
- Crust is the uppermost solid layer of the earth while core is the innermost layer.
- Crust is the thinnest of all the layers. It is about 35 km thick.
- The main elements of the crust are silicon, aluminium and magnesium while the main elements of the core are nickel and iron.
Q 29 – Fill in the blanks
- Lava is the molten magma from interior of the earth’s surface.
2. Like an onion the earth is made up of concentric layers.
3. The crust is about 35 km on the continental mass and 5 km on the ocean floor.
4. Mantle forms about 16% of the earth’s volume.
5. Core has a radius of about 3500 km and has very high temperature and pressure .
6. Limestone under excessive heat and pressure changes into marble
Q 30 –State whether the given statements are true or false:
- Crust is the thickest of all the layers.[False]
2. Core is the innermost layer of the earth.[True]
3. Mantle extends up to the depth of 2900 km.[True]
4. The loose sediments are hardened to form metamorphic rocks.[False]
5. Deccan plateau is made up of basalt.[True]
6. Fossils are remains of dead plants and animals.[True]
Q 31 –Match the contents of Column A with that of Column B
| Column A | Column B |
| 1.Sial | (a) Silica and Alumina |
| 2.Sima | (b) Intrusive igneous rock |
| 3.Nife | (c) Metamorphic rock |
| 4.Basalt | (d) Silica and Alumina |
| 5.Granite | (e) Silica and Magnesium |
| 6.Slate and Marble | (f) Nickel and Ferrous |
Ans –
| Column A | Column B |
| 1.Sial | (d) Silica and Alumina |
| 2.Sima | (e) Silica and Magnesium |
| 3.Nife | (f) Nickel and Ferrous |
| 4.Basalt | (a) Silica and Alumina |
| 5.Granite | (b) Intrusive igneous rock |
| 6.Slate and Marble | (c) Metamorphic rock |
Q 32 – Describe the different layers of the earth.
Ans – The earth is made up of three concentric layers with one inside another—crust, mantle and core.
• Crust— It is the uppermost solid layer of the earth. It is the thinnest of all the layers. It is about 35 km on the continental masses
and only 5 km on the ocean floor.
• Mantle—Below the crust of the earth lies a very thick layer called the mantle. It extends up to a depth of 2900 km below the crust.
The main elements of this layer are silicon and magnesium and is called sima.
• Core—It is the innermost layer with a radius of about 3500 km. It is mainly made up of nickel and iron and is called nife. The
central core has a very high temperature and pressure.
Q 33 – Describe various types of rocks.
Ans – Rocks are of three types, which can be described as under:
(i) Igneous rocks: When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks. Igneous rocks further can be divided into two types- intrusive and extrusive rocks.
(a) Intrusive igneous rocks: Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks.
(b) Extrusive igneous rocks: When molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in
(ii) Sedimentary rocks: When rocks roll down, crack, and hit each other and are broken down into small fragments, these smaller particles are called sediments. These sediments are transported and deposited by wind, water etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks.
(iii) Metamorphic rocks: Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble.