NCERT Textbook: Inside our Earth | Geography for UPSC CSE PDF Download

 Page 1


The earth, our homeland is a dynamic planet. It is
constantly undergoing changes inside and outside. Have
you ever wondered what lies in the interior of the earth?
What is the earth made up of?
INTERIOR OF THE EARTH
Just like an onion, the
earth is made up of
several concentric
layers with one inside
another (Fig. 2.1). The
uppermost layer over
the earth’s surface is
called the crust. It is the
thinnest of all the
layers. It is about 35 km.
on the continental
masses and only 5 km.
on the ocean floors.
The main mineral
constituents of the
continental mass are
silica and alumina. It is
thus called sial (si-silica
and al-alumina). The
oceanic crust mainly
consists of silica and
magnesium; it is therefore
called sima (si-silica and
ma-magnesium) (Fig. 2.2).
Just beneath the crust
is the mantle which
extends up to a depth of
2900 km. below the crust.
2 Inside Our Earth
Do you know?
• The deepest mine in
the world, is in
South Africa. It is
about 4 km. deep. In
search for oil
engineers have dug a
hole about 6 km.
deep.
• To reach to the
centre of the earth
(which is not
possible!) you will
have to dig a hole
6000 km. deep on
the ocean floor.
Crust
Lithosphere
Core-mantle
boundary
Mantle
Outer
core
Inner core
Fig. 2.1: Interior of the Earth
Continental
Crust
Fig. 2.2: Continental Crust and Oceanic Crust
Continent Ocean
Oceanic
Crust
Reprint 2024-25
Page 2


The earth, our homeland is a dynamic planet. It is
constantly undergoing changes inside and outside. Have
you ever wondered what lies in the interior of the earth?
What is the earth made up of?
INTERIOR OF THE EARTH
Just like an onion, the
earth is made up of
several concentric
layers with one inside
another (Fig. 2.1). The
uppermost layer over
the earth’s surface is
called the crust. It is the
thinnest of all the
layers. It is about 35 km.
on the continental
masses and only 5 km.
on the ocean floors.
The main mineral
constituents of the
continental mass are
silica and alumina. It is
thus called sial (si-silica
and al-alumina). The
oceanic crust mainly
consists of silica and
magnesium; it is therefore
called sima (si-silica and
ma-magnesium) (Fig. 2.2).
Just beneath the crust
is the mantle which
extends up to a depth of
2900 km. below the crust.
2 Inside Our Earth
Do you know?
• The deepest mine in
the world, is in
South Africa. It is
about 4 km. deep. In
search for oil
engineers have dug a
hole about 6 km.
deep.
• To reach to the
centre of the earth
(which is not
possible!) you will
have to dig a hole
6000 km. deep on
the ocean floor.
Crust
Lithosphere
Core-mantle
boundary
Mantle
Outer
core
Inner core
Fig. 2.1: Interior of the Earth
Continental
Crust
Fig. 2.2: Continental Crust and Oceanic Crust
Continent Ocean
Oceanic
Crust
Reprint 2024-25
8 OUR ENVIRONMENT
Glossary
The innermost layer is the core with a radius of about
3500 km. It is mainly made up of nickel and iron and is
called nife (ni – nickel and fe – ferrous i.e. iron). The
central core has very high temperature and pressure.
ROCKS AND MINERALS
The earth’s crust is made up of various types of rocks.
Any natural mass of mineral matter that makes up the
earth’s crust is called a rock. Rocks can be of different
colour, size and texture.
There are three major types of rocks: igneous rocks,
sedimentary rocks and metamorphic rocks.
When the molten magma cools, it becomes solid.
Rocks thus formed are called igneous rocks. They are
also called primary rocks. There are two types of igneous
rocks: intrusive rocks and extrusive rocks.
Can you imagine lava coming out from the volcanoes?
Lava is actually fiery red molten magma coming out from
the interior of the earth on its surface. When this molten
lava comes on the earth’s surface, it rapidly cools down
and becomes solid. Rocks formed in such a way on the
crust are called extrusive igneous rocks. They have a
very fine grained structure. For example, basalt. The
Deccan plateau is made up of basalt rocks. Sometimes
the molten magma cools down deep inside the earth’s
crust. Solid rocks so formed are called intrusive igneous
rocks. Since they cool down slowly they form large
grains. Granite is an example of such a rock. Grinding
stones used to prepare paste/powder of spices and grains
are made of granite.
Rocks roll down, crack, and hit each other and are
broken down into small fragments. These smaller particles
are called sediments. These sediments are transported
and deposited by wind, water, etc. These loose
sediments are compressed and hardened to form
layers of rocks. These types of rocks are called
sedimentary rocks. For example, sandstone is
made from grains of sand. These rocks may also
contain fossils of plants, animals and other micro-
organisms that once lived on them.
Igneous and sedimentary rocks can change
into metamorphic rocks under great heat and
pressure (Fig. 2.3). For example, clay changes into
slate and limestone into marble.
Fig. 2.3: Sedimentary rock turned
into a Metamorphic rock
Fossils: The remains
of the dead plants and
animals trapped in
the layers of rocks are
called fossils.
Word Origin
Igneous: Latin word
Ignis meaning fire.
Sedimentary: Latin
word sedimentum
meaning settle down.
Metamorphic: Greek
word metamorphose
meaning change of form.
Do you know?
• The crust forms only
1 per cent of the
volume of the earth,
84 per cent consists
of the mantle and
15 per cent makes
the core.
• The radius of the
earth is 6371 km.
Reprint 2024-25
Page 3


The earth, our homeland is a dynamic planet. It is
constantly undergoing changes inside and outside. Have
you ever wondered what lies in the interior of the earth?
What is the earth made up of?
INTERIOR OF THE EARTH
Just like an onion, the
earth is made up of
several concentric
layers with one inside
another (Fig. 2.1). The
uppermost layer over
the earth’s surface is
called the crust. It is the
thinnest of all the
layers. It is about 35 km.
on the continental
masses and only 5 km.
on the ocean floors.
The main mineral
constituents of the
continental mass are
silica and alumina. It is
thus called sial (si-silica
and al-alumina). The
oceanic crust mainly
consists of silica and
magnesium; it is therefore
called sima (si-silica and
ma-magnesium) (Fig. 2.2).
Just beneath the crust
is the mantle which
extends up to a depth of
2900 km. below the crust.
2 Inside Our Earth
Do you know?
• The deepest mine in
the world, is in
South Africa. It is
about 4 km. deep. In
search for oil
engineers have dug a
hole about 6 km.
deep.
• To reach to the
centre of the earth
(which is not
possible!) you will
have to dig a hole
6000 km. deep on
the ocean floor.
Crust
Lithosphere
Core-mantle
boundary
Mantle
Outer
core
Inner core
Fig. 2.1: Interior of the Earth
Continental
Crust
Fig. 2.2: Continental Crust and Oceanic Crust
Continent Ocean
Oceanic
Crust
Reprint 2024-25
8 OUR ENVIRONMENT
Glossary
The innermost layer is the core with a radius of about
3500 km. It is mainly made up of nickel and iron and is
called nife (ni – nickel and fe – ferrous i.e. iron). The
central core has very high temperature and pressure.
ROCKS AND MINERALS
The earth’s crust is made up of various types of rocks.
Any natural mass of mineral matter that makes up the
earth’s crust is called a rock. Rocks can be of different
colour, size and texture.
There are three major types of rocks: igneous rocks,
sedimentary rocks and metamorphic rocks.
When the molten magma cools, it becomes solid.
Rocks thus formed are called igneous rocks. They are
also called primary rocks. There are two types of igneous
rocks: intrusive rocks and extrusive rocks.
Can you imagine lava coming out from the volcanoes?
Lava is actually fiery red molten magma coming out from
the interior of the earth on its surface. When this molten
lava comes on the earth’s surface, it rapidly cools down
and becomes solid. Rocks formed in such a way on the
crust are called extrusive igneous rocks. They have a
very fine grained structure. For example, basalt. The
Deccan plateau is made up of basalt rocks. Sometimes
the molten magma cools down deep inside the earth’s
crust. Solid rocks so formed are called intrusive igneous
rocks. Since they cool down slowly they form large
grains. Granite is an example of such a rock. Grinding
stones used to prepare paste/powder of spices and grains
are made of granite.
Rocks roll down, crack, and hit each other and are
broken down into small fragments. These smaller particles
are called sediments. These sediments are transported
and deposited by wind, water, etc. These loose
sediments are compressed and hardened to form
layers of rocks. These types of rocks are called
sedimentary rocks. For example, sandstone is
made from grains of sand. These rocks may also
contain fossils of plants, animals and other micro-
organisms that once lived on them.
Igneous and sedimentary rocks can change
into metamorphic rocks under great heat and
pressure (Fig. 2.3). For example, clay changes into
slate and limestone into marble.
Fig. 2.3: Sedimentary rock turned
into a Metamorphic rock
Fossils: The remains
of the dead plants and
animals trapped in
the layers of rocks are
called fossils.
Word Origin
Igneous: Latin word
Ignis meaning fire.
Sedimentary: Latin
word sedimentum
meaning settle down.
Metamorphic: Greek
word metamorphose
meaning change of form.
Do you know?
• The crust forms only
1 per cent of the
volume of the earth,
84 per cent consists
of the mantle and
15 per cent makes
the core.
• The radius of the
earth is 6371 km.
Reprint 2024-25
INSIDE OUR EARTH 9
Let’s do
The Taj Mahal is made of white marble The Red Fort is made of red sandstone
Collect pictures of some monuments and find out which are the rocks
used to build them. Two pictures have been collected for you.
Rocks are very useful to us. The hard rocks are used
for making roads, houses and buildings. You use stones
in many games. For example, seven stones (pitthoo), hop-
scotch (stapu/kit kit), five stones (gitti). Find out some
more such games by asking your grand parents, parents,
neighbours, etc.
You will be surprised to know that 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. You
have already learnt when the
molten magma cools; it solidifies
to become igneous rock. These
igneous rocks are broken down
into small particles that are
transported and deposited to
form 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
melt down to form molten magma.
This molten magma again can
cool down and solidify into
igneous rocks (Fig. 2.4).
Fig. 2.4: Rock Cycle
Reprint 2024-25
Page 4


The earth, our homeland is a dynamic planet. It is
constantly undergoing changes inside and outside. Have
you ever wondered what lies in the interior of the earth?
What is the earth made up of?
INTERIOR OF THE EARTH
Just like an onion, the
earth is made up of
several concentric
layers with one inside
another (Fig. 2.1). The
uppermost layer over
the earth’s surface is
called the crust. It is the
thinnest of all the
layers. It is about 35 km.
on the continental
masses and only 5 km.
on the ocean floors.
The main mineral
constituents of the
continental mass are
silica and alumina. It is
thus called sial (si-silica
and al-alumina). The
oceanic crust mainly
consists of silica and
magnesium; it is therefore
called sima (si-silica and
ma-magnesium) (Fig. 2.2).
Just beneath the crust
is the mantle which
extends up to a depth of
2900 km. below the crust.
2 Inside Our Earth
Do you know?
• The deepest mine in
the world, is in
South Africa. It is
about 4 km. deep. In
search for oil
engineers have dug a
hole about 6 km.
deep.
• To reach to the
centre of the earth
(which is not
possible!) you will
have to dig a hole
6000 km. deep on
the ocean floor.
Crust
Lithosphere
Core-mantle
boundary
Mantle
Outer
core
Inner core
Fig. 2.1: Interior of the Earth
Continental
Crust
Fig. 2.2: Continental Crust and Oceanic Crust
Continent Ocean
Oceanic
Crust
Reprint 2024-25
8 OUR ENVIRONMENT
Glossary
The innermost layer is the core with a radius of about
3500 km. It is mainly made up of nickel and iron and is
called nife (ni – nickel and fe – ferrous i.e. iron). The
central core has very high temperature and pressure.
ROCKS AND MINERALS
The earth’s crust is made up of various types of rocks.
Any natural mass of mineral matter that makes up the
earth’s crust is called a rock. Rocks can be of different
colour, size and texture.
There are three major types of rocks: igneous rocks,
sedimentary rocks and metamorphic rocks.
When the molten magma cools, it becomes solid.
Rocks thus formed are called igneous rocks. They are
also called primary rocks. There are two types of igneous
rocks: intrusive rocks and extrusive rocks.
Can you imagine lava coming out from the volcanoes?
Lava is actually fiery red molten magma coming out from
the interior of the earth on its surface. When this molten
lava comes on the earth’s surface, it rapidly cools down
and becomes solid. Rocks formed in such a way on the
crust are called extrusive igneous rocks. They have a
very fine grained structure. For example, basalt. The
Deccan plateau is made up of basalt rocks. Sometimes
the molten magma cools down deep inside the earth’s
crust. Solid rocks so formed are called intrusive igneous
rocks. Since they cool down slowly they form large
grains. Granite is an example of such a rock. Grinding
stones used to prepare paste/powder of spices and grains
are made of granite.
Rocks roll down, crack, and hit each other and are
broken down into small fragments. These smaller particles
are called sediments. These sediments are transported
and deposited by wind, water, etc. These loose
sediments are compressed and hardened to form
layers of rocks. These types of rocks are called
sedimentary rocks. For example, sandstone is
made from grains of sand. These rocks may also
contain fossils of plants, animals and other micro-
organisms that once lived on them.
Igneous and sedimentary rocks can change
into metamorphic rocks under great heat and
pressure (Fig. 2.3). For example, clay changes into
slate and limestone into marble.
Fig. 2.3: Sedimentary rock turned
into a Metamorphic rock
Fossils: The remains
of the dead plants and
animals trapped in
the layers of rocks are
called fossils.
Word Origin
Igneous: Latin word
Ignis meaning fire.
Sedimentary: Latin
word sedimentum
meaning settle down.
Metamorphic: Greek
word metamorphose
meaning change of form.
Do you know?
• The crust forms only
1 per cent of the
volume of the earth,
84 per cent consists
of the mantle and
15 per cent makes
the core.
• The radius of the
earth is 6371 km.
Reprint 2024-25
INSIDE OUR EARTH 9
Let’s do
The Taj Mahal is made of white marble The Red Fort is made of red sandstone
Collect pictures of some monuments and find out which are the rocks
used to build them. Two pictures have been collected for you.
Rocks are very useful to us. The hard rocks are used
for making roads, houses and buildings. You use stones
in many games. For example, seven stones (pitthoo), hop-
scotch (stapu/kit kit), five stones (gitti). Find out some
more such games by asking your grand parents, parents,
neighbours, etc.
You will be surprised to know that 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. You
have already learnt when the
molten magma cools; it solidifies
to become igneous rock. These
igneous rocks are broken down
into small particles that are
transported and deposited to
form 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
melt down to form molten magma.
This molten magma again can
cool down and solidify into
igneous rocks (Fig. 2.4).
Fig. 2.4: Rock Cycle
Reprint 2024-25
10 OUR ENVIRONMENT
Let’s do
What are the
minerals found in
your state?
Collect some samples
to show in your class.
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?
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
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
Rocks are made up of different minerals. Minerals
are naturally occurring substances which have certain
physical properties and definite chemical composition.
Minerals are very important to humankind. Some are
used as fuels. For example, coal, natural gas and
petroleum. They are also used in industries – iron,
aluminium, gold, uranium, etc, in medicine, in
fertilisers, etc.
Exercises
Reprint 2024-25
Page 5


The earth, our homeland is a dynamic planet. It is
constantly undergoing changes inside and outside. Have
you ever wondered what lies in the interior of the earth?
What is the earth made up of?
INTERIOR OF THE EARTH
Just like an onion, the
earth is made up of
several concentric
layers with one inside
another (Fig. 2.1). The
uppermost layer over
the earth’s surface is
called the crust. It is the
thinnest of all the
layers. It is about 35 km.
on the continental
masses and only 5 km.
on the ocean floors.
The main mineral
constituents of the
continental mass are
silica and alumina. It is
thus called sial (si-silica
and al-alumina). The
oceanic crust mainly
consists of silica and
magnesium; it is therefore
called sima (si-silica and
ma-magnesium) (Fig. 2.2).
Just beneath the crust
is the mantle which
extends up to a depth of
2900 km. below the crust.
2 Inside Our Earth
Do you know?
• The deepest mine in
the world, is in
South Africa. It is
about 4 km. deep. In
search for oil
engineers have dug a
hole about 6 km.
deep.
• To reach to the
centre of the earth
(which is not
possible!) you will
have to dig a hole
6000 km. deep on
the ocean floor.
Crust
Lithosphere
Core-mantle
boundary
Mantle
Outer
core
Inner core
Fig. 2.1: Interior of the Earth
Continental
Crust
Fig. 2.2: Continental Crust and Oceanic Crust
Continent Ocean
Oceanic
Crust
Reprint 2024-25
8 OUR ENVIRONMENT
Glossary
The innermost layer is the core with a radius of about
3500 km. It is mainly made up of nickel and iron and is
called nife (ni – nickel and fe – ferrous i.e. iron). The
central core has very high temperature and pressure.
ROCKS AND MINERALS
The earth’s crust is made up of various types of rocks.
Any natural mass of mineral matter that makes up the
earth’s crust is called a rock. Rocks can be of different
colour, size and texture.
There are three major types of rocks: igneous rocks,
sedimentary rocks and metamorphic rocks.
When the molten magma cools, it becomes solid.
Rocks thus formed are called igneous rocks. They are
also called primary rocks. There are two types of igneous
rocks: intrusive rocks and extrusive rocks.
Can you imagine lava coming out from the volcanoes?
Lava is actually fiery red molten magma coming out from
the interior of the earth on its surface. When this molten
lava comes on the earth’s surface, it rapidly cools down
and becomes solid. Rocks formed in such a way on the
crust are called extrusive igneous rocks. They have a
very fine grained structure. For example, basalt. The
Deccan plateau is made up of basalt rocks. Sometimes
the molten magma cools down deep inside the earth’s
crust. Solid rocks so formed are called intrusive igneous
rocks. Since they cool down slowly they form large
grains. Granite is an example of such a rock. Grinding
stones used to prepare paste/powder of spices and grains
are made of granite.
Rocks roll down, crack, and hit each other and are
broken down into small fragments. These smaller particles
are called sediments. These sediments are transported
and deposited by wind, water, etc. These loose
sediments are compressed and hardened to form
layers of rocks. These types of rocks are called
sedimentary rocks. For example, sandstone is
made from grains of sand. These rocks may also
contain fossils of plants, animals and other micro-
organisms that once lived on them.
Igneous and sedimentary rocks can change
into metamorphic rocks under great heat and
pressure (Fig. 2.3). For example, clay changes into
slate and limestone into marble.
Fig. 2.3: Sedimentary rock turned
into a Metamorphic rock
Fossils: The remains
of the dead plants and
animals trapped in
the layers of rocks are
called fossils.
Word Origin
Igneous: Latin word
Ignis meaning fire.
Sedimentary: Latin
word sedimentum
meaning settle down.
Metamorphic: Greek
word metamorphose
meaning change of form.
Do you know?
• The crust forms only
1 per cent of the
volume of the earth,
84 per cent consists
of the mantle and
15 per cent makes
the core.
• The radius of the
earth is 6371 km.
Reprint 2024-25
INSIDE OUR EARTH 9
Let’s do
The Taj Mahal is made of white marble The Red Fort is made of red sandstone
Collect pictures of some monuments and find out which are the rocks
used to build them. Two pictures have been collected for you.
Rocks are very useful to us. The hard rocks are used
for making roads, houses and buildings. You use stones
in many games. For example, seven stones (pitthoo), hop-
scotch (stapu/kit kit), five stones (gitti). Find out some
more such games by asking your grand parents, parents,
neighbours, etc.
You will be surprised to know that 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. You
have already learnt when the
molten magma cools; it solidifies
to become igneous rock. These
igneous rocks are broken down
into small particles that are
transported and deposited to
form 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
melt down to form molten magma.
This molten magma again can
cool down and solidify into
igneous rocks (Fig. 2.4).
Fig. 2.4: Rock Cycle
Reprint 2024-25
10 OUR ENVIRONMENT
Let’s do
What are the
minerals found in
your state?
Collect some samples
to show in your class.
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?
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
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
Rocks are made up of different minerals. Minerals
are naturally occurring substances which have certain
physical properties and definite chemical composition.
Minerals are very important to humankind. Some are
used as fuels. For example, coal, natural gas and
petroleum. They are also used in industries – iron,
aluminium, gold, uranium, etc, in medicine, in
fertilisers, etc.
Exercises
Reprint 2024-25
INSIDE OUR EARTH 11
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.
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.
Karhai
Ornaments
Pan/Tava
Bell
Hammer
Lamp
Reprint 2024-25