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NCERT solution class 7 Social Science chapter 2 Inside Our Earth

Page No 10:

Question 1:

Answer the following questions.

(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 the crust, the mantle and the core.

(ii) A rock refers to any natural mass of mineral matter that makes up the Earth’s crust.

(iii) Igneous, sedimentary and metamorphic rocks are the three types of rocks.

(iv) Extrusive rocks are formed when the molten magma present inside the Earth’s interior comes out onto the Earth’s surface, cools down and becomes solid. When molten magma cools down and solidifies deep within the Earth’s crust, intrusive rocks are formed.

(v)The transformation of one type of rock into another, under certain conditions and in a cyclical manner is referred to as the rock cycle. For example, igneous rocks, formed as a result of the solidification of molten magma, may break down into small particles, which may then be transported and deposited to form sedimentary rocks. Sedimentary and igneous rocks transform into metamorphic rocks when subjected to heat and pressure. These metamorphic rocks may themselves get broken down to form sedimentary rocks, or they may melt under great heat and pressure to form molten magma, which would then once again solidify to form igneous rocks.

(vi) Some of the uses of rocks are as follows:

(a) For building roads, houses and buildings

(b) For making jewellery

(c) For cutting and drilling purposes

(d) The fossilised remains of plants and animals present in rocks help in scientific research.

(e) The different minerals that make up different rocks are used as fuels, medicines, fertilisers, and in various industries.

(vii) Metamorphic rocks are the rocks that get formed under great heat and pressure. Igneous and sedimentary rocks, when subjected to heat and pressure, get transformed into metamorphic rocks.

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 examples of

(a) Rocks(b) Minerals(c) Fossils

(iv) Rocks which contain fossils are

(a) Sedimentary rocks(b) Metamorphic rocks(c) Igneous rocks

(v) The thinnest layer of the Earth is

(a) Crust(b) Mantle(c) Core

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 examples of

(a) Rocks(b) Minerals(c) Fossils

(iv) Rocks which contain fossils are

(a) Sedimentary rocks(b) Metamorphic rocks(c) Igneous rocks

(v) The thinnest layer of the Earth is

(a) Crust(b) Mantle(c) Core

Question 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(d) Has definite chemical composition
(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 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

Page No 11:

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) The centre of the Earth, lying about 6000 km from the ocean floor, is characterised by extremely high temperature and pressure. There is only molten magma at Earth’s centre. Oxygen is absent from this region. Such conditions do not permit the survival of any living organism. Thus, we cannot go to the centre of the Earth.

(ii) When big rocks break down into small fragments (or sediments), the fragments are transported and deposited by factors like water and wind. The loose sediments compress and harden over the years to form layers and layers of rocks. These rocks are known as sedimentary rocks.

(iii) Limestone is an example of a sedimentary rock. When it is subjected to conditions of extreme heat and pressure, it gets converted into marble, which is a metamorphic rock.

Question 5:

For fun.

(i) What are the minerals most commonly used in the following objects?

(ii) Identify some more objects made up of different minerals.

Answer:

(i)

Objects

Minerals most commonly used in them

Karhai

Iron, copper, stainless steel

Ornaments

Gold, silver

Lamp

Brass, silver, gold

Hammer

Iron, steel, lead, brass

Bell

Brass, silver, gold

Pan/Tava

Iron, steel, aluminium

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