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Chapter 2 Inside Our Earth Solutions

Question - 1 : - What are the three layers of the earth?

Answer - 1 : -

Three Layers of the Earth
  1. Crust
  2. Mantle
  3. Core.

Question - 2 : - What is a rock?

Answer - 2 : -

Rock
1. A mass of mineral matter that makes up the crust of the earth is called rock.
Or
2. Aggregates of minerals are termed as rocks. Examples: See part

Question - 3 : - Name three types of rocks.

Answer - 3 : -

Three Types of Rocks
  1. Igneous Rocks
  2. Sedimentary Rocks
  3. Metamorphic Rocks.

Question - 4 : - How are extrusive and intrusive rocks formed?

Answer - 4 : -

Formation of Extrusive and Intrusive Rocks
1. Due to extreme heat in the interior of the earth, rocks are found in the form of molten material called magma.
2. 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:
  1.  Basalt.
  2.  Deccan Trap is built of basalt.
3. When the molten magma cools down within the interior of the earth, it becomes solid to form intrusive rocks.
Examples:
  1.  Granite.
  2.  Gabro.

Question - 5 : - What do you mean by a rock cycle?

Answer - 5 : -

Rock Cycle
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.

Question - 6 : - What are the uses of rocks?

Answer - 6 : -

Uses of Rocks
  1. Hard rocks are used in making buildings and barrages.
  2. Houses and buildings are built of rocks (stones, slates, granite, marble).
  3. Stones are used in numerous games:
  4. Seven stones (phitthoo).
  5. Hopscotch (stapu, kit).
  6. Five stones (gitti).
  7. Rocks (stones and slates) are used in building bridges, embankments.

Question - 7 : - What are metamorphic rocks?

Answer - 7 : -

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:
  1.  Granite into granite gneiss.
  2.  Coal into slate.
  3.  Slate into schist.
  4.  Limestone into marble.

Question - 8 : -
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 - 8 : - (i)—(a),

(ii)—(b),
(iii)—(b),
(iv)—(a), 
(v)—(a).

Question - 9 : -
Give reasons:
We cannot go to the centre of the earth.

Answer - 9 : -

We cannot go to the centre of the earth because of the following reasons:
  1. The thickness (from crust to the core) is 6371 km. (Radius of the earth).
  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.

Question - 10 : -
Give reasons:
Sedimentary rocks are formed from sediments.

Answer - 10 : -

Sedimentary rocks are formed from sediments because of the following reasons:
  1. Igneous rocks and metamorphic rocks, decompose, disintegrate and wear down due to weathering.
  2. This material is carried away by running water (rivers), wind, glacier.
  3. The material is then deposited in low lying areas and is called sediments.
  4. When sediments are solidified into layers due to pressure from overlying sediments they are called sedimentary rocks.

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