Class 7 Geography Chapter 2

Class 7 Geography  Chapter 2 Inside Our Earth

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) The three layers of the earth are:

• Crust
• Mantle
• Core

(ii) A rock is a natural mass of mineral matter that makes up the earth’s crust.
Rocks can be of different colour, size and texture.

(iii) Three types of rocks are:

• Igneous rocks also known as primary rocks.
• Sedimentary rocks.
• Metamorphic rocks.

(iv) When the molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in this way on the crust are extrusive igneous rocks.
Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are actually intrusive igneous rocks.

(v) 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.

(vi)  Hard rocks are used for making roads, houses and buildings. Stones are used in many games, such as seven stones (pitthoo), hopscotch (stapu/kitkit), Five stones (gitti).Rocks contains minerals.

(vii) When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks. For example, clay changes into slate and limestone 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.