2. Inside Our Earth

NCERT Solutions for Class 7 Social science Chapter 2. Inside Our Earth

Question.1- Answer the following questions-
a) What are the three layers of the Earth?
Answer- a) Crust   b) Core   c) Mantle
b) What is a rock?
Answer- A mass of mineral matter that makes up the crust of the earth is called rock.
c) Name three types of rocks.
Answer- 1. Igneous  2. sedimentary  3. metamorphic
d) How are extrusive and intrusive rocks formed?
Answer- 1. Extrusive rocks - 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)
2. Intrusive rocks :-When the molten magma cools down within the interior of the earth, it becomes solid to form intrusive rocks.   Examples  -   Granite
e) What do you mean by a rock cycle?
Answer-  Igneous rocks change into sedimentary rocks, igneous and sedimentary rocks under heat and pressure change into metamorphic rocks, metamorphic rocks into igneous rocks or sedimentary rocks due to melting or wearing down. This process is called the rock cycle.
f) What are the uses of rocks?
Answer- Some of the uses of rocks are as follows-
1. For building roads, houses and buildings.
2. For making jewellery.
3. For cutting and drilling purposes.
 
g) What are metamorphic rocks?
Answer- 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-  Limestone into marble.
 
Question.2 Tick the correct answer-
 
(1) The rock which is made up of molten magma is
a) Igneous
b) Sedimentary
c) Metamorphic
 
(2) The innermost layer of the Earth is
a) Crust
b) Core
c) Mantle
 
(3) Gold, petroleum and coal are examples of
a) Rocks
b) Minerals
c) Fossils
 
(4) Rocks which contain fossils are
a) Sedimentary rocks
b) Metamorphic rocks
c) Igneous rocks
 
(5) The thinnest layer of the Earth is
a) Crust
b) Mantle
c) Core
 
Answer- 1. a) Igneous     2. b) Core    
3. b) Minerals    4. a) Sedimentary rocks       
 5. a) Crust
 
Question.3 Match the following-
Answer-
 

(1) Core

(e) Innermost layer

(2) Minerals

(d) Has definite chemical composition

(3) Rocks

(b) Used for roads and buildings

(4) Clay

(f) Changes into slate

(5) Sial

(c) Made of silicon and alumina
 
Question.4 Give reasons-
 
(a) We cannot go to the centre of the Earth.
Answer- 1.The thickness (from crust to the core) is 6371 km.
2. Temperature increases with depth @ 1°C per 32 metre.
3.There is extreme heat and pressure of overlying rocks, everything is in a molten state.
4.There is no oxygen to survive.
 
(b) Sedimentary rocks are formed from sediments.
Answer- Igneous rocks and metamorphic rocks, decompose, disintegrate and wear down due to weathering. This material is carried away by running water (rivers), wind, glacier.  The material is then deposited in low lying areas and is called sediments. When sediments are solidified into layers due to pressure from overlying sediments they are called sedimentary rocks.
 
(c) Limestone is changed into marble.
Answer-  The overlying layers of rocks put pressure on the underlying rocks.
From the surface to the interior of the earth, temperature and heat go on increasing. Due to pressure and heat, the original limestone changes into marble.