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Inside Our Earth |Exercises solution | Class 7| Our Environment UPSC

 1. Answer the following questions.


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

Answer:

The following are three layers of the earth:

  • Crust
  • Mantle
  • Core
Crust=continental made up by Sial( Silica and Aluminium) + Oceanic plate made up by Sima( silica and Magnesium). It is on average 35 km in depth and comprises 1 % of earth mass.

Mantle; it is up to 2900 km depth consist of 84 % of the mass.

Core; its radius is about 3500 km. The core is made up of nife( nickel + ferrous). It is 15 % of the earth masses.


(ii) What is a rock?

Answer:

The natural mass of mineral matter that makes the crust is called rock.


(iii) Name three types of rocks.

Answer:

There are three types of  rocks:

  • Igneous rocks
  • Sedimentary rocks
  • Metamorphic rocks
Igneous rock :
  • Igneous rock is also called primary rock, it is formed after the cooling of magma.
  • For example, Basalt rock( extrusive igneous rock), Granite ( intrusive igneous rock)
Sedimentary rocks:
  • A smaller segment of broken rocks is called sediments. These sediments are compressed and harden leads to the formation of sedimentary rocks.
  • For example, Sandstone.
Metamorphic rocks:
  • Igneous rock and sedimentary rock changes to metamorphic rock under great heat and pressure.
  • For example, clay changes into a slate. Limestone into marble.

(iv) How are extrusive and intrusive rocks formed?
Answer:
  • When volcanos molten magma cools on the earth's surface. They rapidly cool down and forms extrusive rock. It has finer particles. For example, Basalt rock.
  • When volcanos molten magma cools inside the earth's surface, they cool slowly, hence they have larger grains; it is called intrusive rocks. For example, Granite rock.

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

Answer:

  • One type of rock changes to other rock types in a cyclic manner under certain conditions is called the rock cycle.
  • Molten lava cools and forms igneous rock. 
  • Igneous rock breaks into sediments and after compression of sediments formed the sedimentary rock.
  • Both sedimentary and igneous rock can be converted into the metamorphic rock under great heat and pressure.
  • Sedimentary rock and metamorphic rock can be converted into molten magma under certain heat and pressure. 


(vi) What are the uses of rocks?

Answer:

  • Rocks are used in making buildings. For Example, the Taj Mahal is made up of White Marble ( Metamorphic rock).
  • Red Fort is made up of red sandstone( sedimentary rock)
  • The rock contains various minerals that are used for various purposes such as iron-making, aluminum, gold, medicins.
  • Rock also contains coal, petroleum, and natural gases.


(vii) What are metamorphic rocks?

Answer:

  • Igneous rock and sedimentary rock particles get converted into the metamorphic rock under great heat and temperature 
  • For example, clay changes into a slate. Limestone into marble.

2. Tick the correct answer.


(i) The rock which is made up of molten magma is

(a) Igneous

(b) Sedimentary

(c) Metamorphic

Answer:

a) Igneous


(ii) The innermost layer of the earth is

(a) Crust 

(b) Core 

(c) Mantle

Answer:

b) Core


(iii) Gold, petroleum, and coal are examples of

(a) Rocks 

(b) Minerals

(c) Fossils

Answer:

b) Minerals.


(iv) Rocks that contain fossils are

(a) Sedimentary rocks

(b) Metamorphic rocks

(c) Igneous rocks

Answer:

a) Sedimentary rocks.


(v) The thinnest layer of the earth is

(a) Crust 

(b) Mantle 

(c) Core

Answer:

a) Crust


3. Match the following.

(i) Core                             (a) Earth’s surface

(ii) Minerals                     (b) Used for roads and buildings

(iii) Rocks                         (c) Made of silicon and alumina

(iv) Clay                             

(v) Sial                                (e) Innermost layer

                                             (f) Changes into slate

                                            (g) Process of transformation of the rock

Answer:

(i) Core                              (e) Innermost layer 

(ii) Minerals                     (d) Has the definite chemical composition

(iii) Rocks                        (b) Used for roads and buildings 

(iv) Clay                            (f) Changes into slate

(v) Sial                               (c) Made of silicon and alumina

                                            

                                           

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