Inside Our Earth Geography Class 7 Chapter 2 Question & Answer

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Question 1. Answer the following questions briefly.

(i) What are the three layers of the earth?

(ii) What is a rock?

(iii) Name three types of rocks.

(iv) How are extrusive and intrusive rocks formed?

(v) What do you mean by a rock cycle?

(vi) What are the uses of rocks?

(vii) What are metamorphic rocks?

Answer:

(i) What are the three layers of the earth?

The earth is made up of three main layers:

1. Crust: This is the outermost layer where we live. It’s thin and solid, and it’s made up of various types of rocks.
2. Mantle: The layer beneath the crust. It’s made of hot, dense, semi-solid rock that moves slowly.
3. Core: The innermost layer. It’s divided into two parts:
   • Outer core: Liquid and mainly composed of iron and nickel.
   • Inner core: Solid, due to extreme pressure, and also made of iron and nickel.

(ii) What is a rock?

A rock is a natural solid material made up of one or more minerals. Rocks are the building blocks of the Earth’s crust. They can be different in:

• Color (like black, gray, red, etc.)
• Size (from tiny pebbles to huge mountains)
• Texture (smooth, rough, hard, or soft)

(iii) Name three types of rocks.

There are three major types of rocks:

1. Igneous Rocks: These are also called “primary” rocks because they form directly from molten magma or lava when it cools and solidifies.
2. Sedimentary Rocks: These form when small particles of other rocks or organic materials settle in layers and get pressed over time.
3. Metamorphic Rocks: These form when existing rocks are changed by heat, pressure, or chemical processes deep inside the earth.

(iv) How are extrusive and intrusive rocks formed?

• Extrusive Rocks are formed above the earth’s surface. When molten lava from a volcano erupts, it cools down quickly and hardens into solid rock. These rocks have small crystals because they cool quickly.
  • Example: Basalt.
• Intrusive Rocks are formed below the earth’s surface. Here, magma slowly cools down and hardens inside the earth, forming rocks with large crystals because of the slow cooling.
  • Example: Granite.

(v) What do you mean by a rock cycle?

The rock cycle is a continuous process where rocks change from one type to another over time. Here’s how it works:

1. Igneous rocks break down into tiny particles and settle to form sedimentary rocks.
2. These sedimentary rocks can then be pushed deep inside the earth, where heat and pressure change them into metamorphic rocks.
3. If these metamorphic rocks melt, they become molten magma, which can cool to form new igneous rocks.

This process keeps repeating in nature, like a cycle.

(vi) What are the uses of rocks?

Rocks have many practical uses in everyday life:

• Hard rocks (like granite) are used for constructing buildings, roads, and monuments.
• Stones (smaller rocks) are also used in various games like:
  • Seven stones (also known as “pitthoo”)
  • Hopscotch (called “stapu” or “kitkit”)
  • Five stones (a game called “gitti”)

(vii) What are metamorphic rocks?

Metamorphic rocks are formed when igneous or sedimentary rocks are subjected to intense heat and pressure deep inside the earth. The structure and composition of the rock change, creating a new type of rock.

• For example:
  • Clay turns into slate.
  • Limestone changes into marble.

Question 2. Tick the correct answer.
(i) The rock which is made up of molten magma is
(a) Igneous (b) Sedimentary
(c) Metamorphic.

(ii) The innermost layer of the earth is
(a) Crust (b) Core
(c) Mantle.

(iii) Gold, petroleum and coal are example of
(a) Rocks (b) Minerals
(c) Fossils.

(iv) Rocks which contain fossils are
(a) Sedimentary rocks (b) Metamorphic rocks
(c) Igneons rocks.

(v) The thinnest layer of the earth is
(a) Crust (b) Mantle
(c) Core.

Answer: (i)—(a), (ii)—(b), (iii)—(b), (iv)—(a), (v)—(a).

Question 4. Give reasons:
(i) We cannot go to the centre of the earth.
(ii) Sedimentary rocks are formed from sediments.
(iii) Limestone is changed into marble.

Answer: (i) To reach the centre of the earth one will have to dig a hole 6000 km. deep on the ocean floor. This is quite impossible and therefore we cannot go to the centre of the earth.
(ii) Rocks break down into small fragments known as sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks known as sedimentary rocks.
(iii) Limestone is changed into marble because igneous and sedimentary rocks change into metamorphic rocks under a great heat and pressure.

Short Answer Type Questions

Question 1. What is called the uppermost layer of the earth? [Imp.]

Answer: It is called the crust.

Question 2. What is the special feature of this layer? {Imp.]

Answer. It is the thinnest of all the layers

Question 3. Name the main mineral constituent of the continental mass.

Answer: Silica and alumina

Question 4. Name the constituents of the oceanic crust. [V. Imp.]

Answer: Silica and magnesium.

Question 5. What is the radius of the core?

Answer: The radius of the core is about 3500 km.

Question 6. What are the main constituents of the core?

Answer: The main constituents of the core are nickel and iron. It is usually known as nife.

Question 7. What is the earth’s crust made of? [V.Imp.]

Answer: It is made up of different types of rocks.

Question 8. What are called igneous rocks?

Answer: When the molten magma cools, it becomes solid. Rocks formed in this way are called igneous rocks.

Question 9. What are fossils?

Answer: The remains of the dead plant and animals trapped in the layers of rocks are called fossils.

Question 10. What happens when igneous and sedimentary rocks go under great heat and pressure?

Answer: They change into metamorphic rocks.

Short Answer Type Questions

Question 1. What are minerals? How are they useful for mankind? [V. Imp.]

Answer: Minerals are naturally occurring substances which have certain physical properties and definite chemical composition.
Minerals are very useful for mankind. Some minerals like coal, natural gas and petroleum are used as fuels. They are also used in industries. Iron, aluminium, gold, uranium etc. are used in medicine, in Fertilizers etc.

Long Answer Type Questions

Question 1. Mention various types of rocks IV. Imp.]

Answer: Rocks are of the three types:

1. Igneous rocks
a)Sedimentary rocks
b)Metamorphic rocks
c)Igneous rocks. When the molten magma cools, it becomes solid. Rocks formed in this way are called igneous rocks. They are also called primary rocks. They are of two types—intrusive rocks and extrusive rocks.
2. Extrusive rocks.When molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in this way on the crust Eire called extrusive igneous rocks. For example, basalt.
3. Intrusive rocks. Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly they form large grains. For example, granite.
4. Sedimentary rocks. Small fragments of rocks are called sediments. These sediments are transported and deposited by wind, water, etc.These loose sediments are compressed and hardened to form sedimentary rocks. For example, sandstone is made from grains of sand.
5. Metamorphic rocks. When igneous and sedimentary rocks Eire subjected to great heat and pressure they chsmge into metamorphic rocks. For example, clay changes into slate and limestone into marble.

Question 2. What do you know about the interior of the earth? [V. Imp.]

Answer: Our earth is made up of several concentric layers with one inside another. These layers are three in number—crust, mantle smd core.
Crust. It is the uppermost layer over the earth’s surface. It is the thinnest of all the layers. It is about 35 km on the continential masses and only 5 km 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 2900 km below the crust
Core:It is the innermost layer. Its radius is about 3500 km. 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.