NCERT Textbook: Our Home: Earth, a Unique Life Sustaining Planet | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


210
Curiosity — Textbook of Science for Grade 8
Our Home: 
Earth, a Unique Life 
Sustaining Planet 
13
Probe and ponder
 z What do you think Earth would look like if there were no life 
on it at all?
 z Life on Earth has survived for billions of years. What allows it 
to keep going despite major changes and disasters?
 z Why don’t dogs lay eggs? Or hens give birth to live chicks?
 z If a spaceship carried soil and water to Mars, could plants start 
growing there?
 Share your questions 
 
  ?
Chapter 13.indd   210 Chapter 13.indd   210 01-07-2025   12:21:04 01-07-2025   12:21:04
Page 2


210
Curiosity — Textbook of Science for Grade 8
Our Home: 
Earth, a Unique Life 
Sustaining Planet 
13
Probe and ponder
 z What do you think Earth would look like if there were no life 
on it at all?
 z Life on Earth has survived for billions of years. What allows it 
to keep going despite major changes and disasters?
 z Why don’t dogs lay eggs? Or hens give birth to live chicks?
 z If a spaceship carried soil and water to Mars, could plants start 
growing there?
 Share your questions 
 
  ?
Chapter 13.indd   210 Chapter 13.indd   210 01-07-2025   12:21:04 01-07-2025   12:21:04
Chapter 13?—?Our Home: Earth, a Unique Life Sustaining Planet
211
We have now reached the final chapter of this book, the 
concluding chapter in our scientific journey through the middle 
stage. It is time to put together all that we have seen and learnt 
and try to understand why our home, planet Earth, is like 
no other place in the known universe. As you have learnt in 
Curiosity, Grades 6 and 7, the Earth is a planet orbiting the Sun. 
However, it is not just any planet. It is a planet that sustains 
life — full of diverse landscapes, from towering mountains 
and vast oceans to endless deserts and lush forests. Today, our 
satellites allow us to take amazing pictures of our planet. The 
image in the beginning  page was taken by an Indian Space 
Research Organisation (ISRO) Earth Observation Satellite and 
made by combining nearly 3000 smaller images, like pieces of 
a mosaic. Although it looks beautiful, it’s a false colour image, 
where scientists use different colours to show different types of 
information. These satellite images help us study plants on land 
and tiny organisms in the ocean, and can even detect things 
like ocean temperature, oil spills, and wind direction. In this 
chapter, we will uncover the unique conditions that make Earth 
the perfect home for living beings.
13.1 Why Is Earth a Unique Planet?
What makes the Earth so special? While there are perhaps 
billions of planets in the universe, Earth is the only one where 
life, as we know today, exists and thrives in all its forms.
Have you ever wondered 
where all life on Earth 
actually exists? All the 
mountains, rivers, forests, 
animals, and people are 
found on just a very thin 
layer on the surface of our 
planet. From the tallest 
mountain to the deepest 
ocean trench, the crust, 
where all of life exists, is 
tiny compared to the size of 
Earth. If Earth were the size 
of an apple, the crust would 
be as thin as the apple’s 
skin as shown in Fig. 13.1. 
This delicate, life supporting layer is what makes Earth truly 
special.
crust
Fig. 13.1: The Earth’s crust is like the thin skin of an apple  
Crust
Upper mantle
Lower mantle
Outer core
Inner core
Chapter 13.indd   211 Chapter 13.indd   211 01-07-2025   12:21:24 01-07-2025   12:21:24
Page 3


210
Curiosity — Textbook of Science for Grade 8
Our Home: 
Earth, a Unique Life 
Sustaining Planet 
13
Probe and ponder
 z What do you think Earth would look like if there were no life 
on it at all?
 z Life on Earth has survived for billions of years. What allows it 
to keep going despite major changes and disasters?
 z Why don’t dogs lay eggs? Or hens give birth to live chicks?
 z If a spaceship carried soil and water to Mars, could plants start 
growing there?
 Share your questions 
 
  ?
Chapter 13.indd   210 Chapter 13.indd   210 01-07-2025   12:21:04 01-07-2025   12:21:04
Chapter 13?—?Our Home: Earth, a Unique Life Sustaining Planet
211
We have now reached the final chapter of this book, the 
concluding chapter in our scientific journey through the middle 
stage. It is time to put together all that we have seen and learnt 
and try to understand why our home, planet Earth, is like 
no other place in the known universe. As you have learnt in 
Curiosity, Grades 6 and 7, the Earth is a planet orbiting the Sun. 
However, it is not just any planet. It is a planet that sustains 
life — full of diverse landscapes, from towering mountains 
and vast oceans to endless deserts and lush forests. Today, our 
satellites allow us to take amazing pictures of our planet. The 
image in the beginning  page was taken by an Indian Space 
Research Organisation (ISRO) Earth Observation Satellite and 
made by combining nearly 3000 smaller images, like pieces of 
a mosaic. Although it looks beautiful, it’s a false colour image, 
where scientists use different colours to show different types of 
information. These satellite images help us study plants on land 
and tiny organisms in the ocean, and can even detect things 
like ocean temperature, oil spills, and wind direction. In this 
chapter, we will uncover the unique conditions that make Earth 
the perfect home for living beings.
13.1 Why Is Earth a Unique Planet?
What makes the Earth so special? While there are perhaps 
billions of planets in the universe, Earth is the only one where 
life, as we know today, exists and thrives in all its forms.
Have you ever wondered 
where all life on Earth 
actually exists? All the 
mountains, rivers, forests, 
animals, and people are 
found on just a very thin 
layer on the surface of our 
planet. From the tallest 
mountain to the deepest 
ocean trench, the crust, 
where all of life exists, is 
tiny compared to the size of 
Earth. If Earth were the size 
of an apple, the crust would 
be as thin as the apple’s 
skin as shown in Fig. 13.1. 
This delicate, life supporting layer is what makes Earth truly 
special.
crust
Fig. 13.1: The Earth’s crust is like the thin skin of an apple  
Crust
Upper mantle
Lower mantle
Outer core
Inner core
Chapter 13.indd   211 Chapter 13.indd   211 01-07-2025   12:21:24 01-07-2025   12:21:24
212
Curiosity — Textbook of Science for Grade 8
Let us conduct an activity to list out some features of the 
Earth that you think make it special.
Activity 13.1: Let us find out
 z List some features of the Earth that we often take for 
granted, but are interesting and important to us. Write them 
in Table 13.1. We have filled in a few for you.
S.No. Interesting features of the Earth
1.
The air we breathe doesn’t fly off and disappear into space. 
(We learnt in Chapter 7 that the particles of a gas move freely, 
and gases do not have a fixed volume)
2.
We can stand on the ground held by gravity (as we learnt in 
Chapter 5), but our heart can pump blood up to our head.
3.
4.
Table 13.1: Interesting features about the Earth
Discuss the features you have listed with your teacher and 
friends. You may realise that the Earth is interesting and important 
to us in many ways. It provides us with the air that we breathe, the 
water that we drink, and the soil that helps in growing crops. The 
Earth also provides us materials like rock and timber with which 
we build our homes, buildings, and roads. You must be curious 
to know what makes the Earth a unique planet which not only 
allows life like us to exist but also sustains it.
13.2  What Do the Planets of Our Solar System 
Look Like?
In Curiosity, Grade 6, you had studied the solar system in the 
chapter ‘Beyond Earth’. Let us recall some of the things we had 
learnt. Our solar system has eight planets that go around the Sun 
in nearly circular orbits. In order of their increasing distance 
from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter, 
I wonder what makes the Earth 
unique for living beings to grow 
and survive!
Chapter 13.indd   212 Chapter 13.indd   212 6/28/2025   6:15:36 PM 6/28/2025   6:15:36 PM
Page 4


210
Curiosity — Textbook of Science for Grade 8
Our Home: 
Earth, a Unique Life 
Sustaining Planet 
13
Probe and ponder
 z What do you think Earth would look like if there were no life 
on it at all?
 z Life on Earth has survived for billions of years. What allows it 
to keep going despite major changes and disasters?
 z Why don’t dogs lay eggs? Or hens give birth to live chicks?
 z If a spaceship carried soil and water to Mars, could plants start 
growing there?
 Share your questions 
 
  ?
Chapter 13.indd   210 Chapter 13.indd   210 01-07-2025   12:21:04 01-07-2025   12:21:04
Chapter 13?—?Our Home: Earth, a Unique Life Sustaining Planet
211
We have now reached the final chapter of this book, the 
concluding chapter in our scientific journey through the middle 
stage. It is time to put together all that we have seen and learnt 
and try to understand why our home, planet Earth, is like 
no other place in the known universe. As you have learnt in 
Curiosity, Grades 6 and 7, the Earth is a planet orbiting the Sun. 
However, it is not just any planet. It is a planet that sustains 
life — full of diverse landscapes, from towering mountains 
and vast oceans to endless deserts and lush forests. Today, our 
satellites allow us to take amazing pictures of our planet. The 
image in the beginning  page was taken by an Indian Space 
Research Organisation (ISRO) Earth Observation Satellite and 
made by combining nearly 3000 smaller images, like pieces of 
a mosaic. Although it looks beautiful, it’s a false colour image, 
where scientists use different colours to show different types of 
information. These satellite images help us study plants on land 
and tiny organisms in the ocean, and can even detect things 
like ocean temperature, oil spills, and wind direction. In this 
chapter, we will uncover the unique conditions that make Earth 
the perfect home for living beings.
13.1 Why Is Earth a Unique Planet?
What makes the Earth so special? While there are perhaps 
billions of planets in the universe, Earth is the only one where 
life, as we know today, exists and thrives in all its forms.
Have you ever wondered 
where all life on Earth 
actually exists? All the 
mountains, rivers, forests, 
animals, and people are 
found on just a very thin 
layer on the surface of our 
planet. From the tallest 
mountain to the deepest 
ocean trench, the crust, 
where all of life exists, is 
tiny compared to the size of 
Earth. If Earth were the size 
of an apple, the crust would 
be as thin as the apple’s 
skin as shown in Fig. 13.1. 
This delicate, life supporting layer is what makes Earth truly 
special.
crust
Fig. 13.1: The Earth’s crust is like the thin skin of an apple  
Crust
Upper mantle
Lower mantle
Outer core
Inner core
Chapter 13.indd   211 Chapter 13.indd   211 01-07-2025   12:21:24 01-07-2025   12:21:24
212
Curiosity — Textbook of Science for Grade 8
Let us conduct an activity to list out some features of the 
Earth that you think make it special.
Activity 13.1: Let us find out
 z List some features of the Earth that we often take for 
granted, but are interesting and important to us. Write them 
in Table 13.1. We have filled in a few for you.
S.No. Interesting features of the Earth
1.
The air we breathe doesn’t fly off and disappear into space. 
(We learnt in Chapter 7 that the particles of a gas move freely, 
and gases do not have a fixed volume)
2.
We can stand on the ground held by gravity (as we learnt in 
Chapter 5), but our heart can pump blood up to our head.
3.
4.
Table 13.1: Interesting features about the Earth
Discuss the features you have listed with your teacher and 
friends. You may realise that the Earth is interesting and important 
to us in many ways. It provides us with the air that we breathe, the 
water that we drink, and the soil that helps in growing crops. The 
Earth also provides us materials like rock and timber with which 
we build our homes, buildings, and roads. You must be curious 
to know what makes the Earth a unique planet which not only 
allows life like us to exist but also sustains it.
13.2  What Do the Planets of Our Solar System 
Look Like?
In Curiosity, Grade 6, you had studied the solar system in the 
chapter ‘Beyond Earth’. Let us recall some of the things we had 
learnt. Our solar system has eight planets that go around the Sun 
in nearly circular orbits. In order of their increasing distance 
from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter, 
I wonder what makes the Earth 
unique for living beings to grow 
and survive!
Chapter 13.indd   212 Chapter 13.indd   212 6/28/2025   6:15:36 PM 6/28/2025   6:15:36 PM
Chapter 13?—?Our Home: Earth, a Unique Life Sustaining Planet
213
Saturn, Uranus, and Neptune. Out of all these planets, Mercury, 
Venus, Earth, and Mars, are relatively small and rocky planets, 
while Jupiter, Saturn, Uranus, and Neptune are large planets, 
mostly made of gases.
Let us find out more about the planets in the solar system by 
performing Activity 13.2.
Activity 13.2: Let us find out
 z Collect information about the temperature and size of 
the planets in the solar system, and check if they have an 
atmosphere.
 z You may collect this information from books in your school 
library, trusted websites, or discuss with your teachers.
 z Fill out the missing information in Table 13.2.
S.No. Planet
Average 
temperature 
(
o
C)
Radius, 
compared to 
the Earth
Has an 
atmosphere?
1. Mercury 170 No
2. Venus 450 0.95 Yes
3. Earth 15 1 Yes
4.
5. 11
6.
7.
8. –200 4
Table 13.2: Planets in our solar system
We know that all planets in the solar system get their energy 
from the Sun. Thus, when a planet is close to the Sun, it would 
be very hot. As we move away from the Sun, planets should get 
colder. Is this what you found in Table 13.2? This is generally 
correct, except that Venus, the second planet from the Sun has 
the highest average temperature and is the hottest planet. Why is 
this so? 
Venus is the hottest planet not because it is the closest 
to the Sun, but because its thick atmosphere traps heat.  
Chapter 13.indd   213 Chapter 13.indd   213 6/28/2025   6:15:36 PM 6/28/2025   6:15:36 PM
Page 5


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Curiosity — Textbook of Science for Grade 8
Our Home: 
Earth, a Unique Life 
Sustaining Planet 
13
Probe and ponder
 z What do you think Earth would look like if there were no life 
on it at all?
 z Life on Earth has survived for billions of years. What allows it 
to keep going despite major changes and disasters?
 z Why don’t dogs lay eggs? Or hens give birth to live chicks?
 z If a spaceship carried soil and water to Mars, could plants start 
growing there?
 Share your questions 
 
  ?
Chapter 13.indd   210 Chapter 13.indd   210 01-07-2025   12:21:04 01-07-2025   12:21:04
Chapter 13?—?Our Home: Earth, a Unique Life Sustaining Planet
211
We have now reached the final chapter of this book, the 
concluding chapter in our scientific journey through the middle 
stage. It is time to put together all that we have seen and learnt 
and try to understand why our home, planet Earth, is like 
no other place in the known universe. As you have learnt in 
Curiosity, Grades 6 and 7, the Earth is a planet orbiting the Sun. 
However, it is not just any planet. It is a planet that sustains 
life — full of diverse landscapes, from towering mountains 
and vast oceans to endless deserts and lush forests. Today, our 
satellites allow us to take amazing pictures of our planet. The 
image in the beginning  page was taken by an Indian Space 
Research Organisation (ISRO) Earth Observation Satellite and 
made by combining nearly 3000 smaller images, like pieces of 
a mosaic. Although it looks beautiful, it’s a false colour image, 
where scientists use different colours to show different types of 
information. These satellite images help us study plants on land 
and tiny organisms in the ocean, and can even detect things 
like ocean temperature, oil spills, and wind direction. In this 
chapter, we will uncover the unique conditions that make Earth 
the perfect home for living beings.
13.1 Why Is Earth a Unique Planet?
What makes the Earth so special? While there are perhaps 
billions of planets in the universe, Earth is the only one where 
life, as we know today, exists and thrives in all its forms.
Have you ever wondered 
where all life on Earth 
actually exists? All the 
mountains, rivers, forests, 
animals, and people are 
found on just a very thin 
layer on the surface of our 
planet. From the tallest 
mountain to the deepest 
ocean trench, the crust, 
where all of life exists, is 
tiny compared to the size of 
Earth. If Earth were the size 
of an apple, the crust would 
be as thin as the apple’s 
skin as shown in Fig. 13.1. 
This delicate, life supporting layer is what makes Earth truly 
special.
crust
Fig. 13.1: The Earth’s crust is like the thin skin of an apple  
Crust
Upper mantle
Lower mantle
Outer core
Inner core
Chapter 13.indd   211 Chapter 13.indd   211 01-07-2025   12:21:24 01-07-2025   12:21:24
212
Curiosity — Textbook of Science for Grade 8
Let us conduct an activity to list out some features of the 
Earth that you think make it special.
Activity 13.1: Let us find out
 z List some features of the Earth that we often take for 
granted, but are interesting and important to us. Write them 
in Table 13.1. We have filled in a few for you.
S.No. Interesting features of the Earth
1.
The air we breathe doesn’t fly off and disappear into space. 
(We learnt in Chapter 7 that the particles of a gas move freely, 
and gases do not have a fixed volume)
2.
We can stand on the ground held by gravity (as we learnt in 
Chapter 5), but our heart can pump blood up to our head.
3.
4.
Table 13.1: Interesting features about the Earth
Discuss the features you have listed with your teacher and 
friends. You may realise that the Earth is interesting and important 
to us in many ways. It provides us with the air that we breathe, the 
water that we drink, and the soil that helps in growing crops. The 
Earth also provides us materials like rock and timber with which 
we build our homes, buildings, and roads. You must be curious 
to know what makes the Earth a unique planet which not only 
allows life like us to exist but also sustains it.
13.2  What Do the Planets of Our Solar System 
Look Like?
In Curiosity, Grade 6, you had studied the solar system in the 
chapter ‘Beyond Earth’. Let us recall some of the things we had 
learnt. Our solar system has eight planets that go around the Sun 
in nearly circular orbits. In order of their increasing distance 
from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter, 
I wonder what makes the Earth 
unique for living beings to grow 
and survive!
Chapter 13.indd   212 Chapter 13.indd   212 6/28/2025   6:15:36 PM 6/28/2025   6:15:36 PM
Chapter 13?—?Our Home: Earth, a Unique Life Sustaining Planet
213
Saturn, Uranus, and Neptune. Out of all these planets, Mercury, 
Venus, Earth, and Mars, are relatively small and rocky planets, 
while Jupiter, Saturn, Uranus, and Neptune are large planets, 
mostly made of gases.
Let us find out more about the planets in the solar system by 
performing Activity 13.2.
Activity 13.2: Let us find out
 z Collect information about the temperature and size of 
the planets in the solar system, and check if they have an 
atmosphere.
 z You may collect this information from books in your school 
library, trusted websites, or discuss with your teachers.
 z Fill out the missing information in Table 13.2.
S.No. Planet
Average 
temperature 
(
o
C)
Radius, 
compared to 
the Earth
Has an 
atmosphere?
1. Mercury 170 No
2. Venus 450 0.95 Yes
3. Earth 15 1 Yes
4.
5. 11
6.
7.
8. –200 4
Table 13.2: Planets in our solar system
We know that all planets in the solar system get their energy 
from the Sun. Thus, when a planet is close to the Sun, it would 
be very hot. As we move away from the Sun, planets should get 
colder. Is this what you found in Table 13.2? This is generally 
correct, except that Venus, the second planet from the Sun has 
the highest average temperature and is the hottest planet. Why is 
this so? 
Venus is the hottest planet not because it is the closest 
to the Sun, but because its thick atmosphere traps heat.  
Chapter 13.indd   213 Chapter 13.indd   213 6/28/2025   6:15:36 PM 6/28/2025   6:15:36 PM
214
Curiosity — Textbook of Science for Grade 8
The air on Venus is almost entirely made up of carbon 
dioxide gas, which does not let the heat escape. This 
is called the greenhouse effect (Fig. 13.2), and it 
makes Venus even hotter than Mercury, which is 
relatively closer to the Sun. On the Earth also, gases 
like carbon dioxide in the atmosphere trap heat 
by absorbing the radiation given off by the Earth, 
after it gets warmed by the Sun. Thus, greenhouse 
effect plays an important role in maintaining just 
the right temperature on Earth.
A step further
The greenhouse effect that causes 
a planet like Venus and Earth to 
trap heat does not work the same 
way as a greenhouse for growing 
plants in a cool climate. On Venus 
or Earth, gases like carbon dioxide 
in the atmosphere trap heat by 
absorbing the radiation given off 
by the Earth, after it gets warmed 
by the Sun. A plant greenhouse, on 
the other hand, traps warmed air 
simply because it is a closed space, usually with glass walls (Fig. 13.3). 
It heats up during the day, but the air stays in and the heat does not 
escape easily. So while both keep things warm, they do it differently!
Fig. 13.3: Greenhouse for plants
13.3 What Makes the Earth Suitable for Life to  
          Exist ?
13.3.1 Position of the Earth
The most important reason why the Earth 
can support life is its distance from the 
Sun. It is just at the right distance, where 
the temperature allows water to exist in a 
liquid form. If the Earth were closer to the 
Sun, it would be too hot and all the water 
would evaporate; if it were farther away, 
it would be too cold, and all the water 
would freeze.  In such extreme conditions, 
it would have been impossible for most 
life forms — especially plants, animals, and 
humans — to grow and thrive on Earth. 
Although some microbes, like certain 
 Fig. 13.4: The habitable zone  
around a star
Habitable zone
Too hot Just right
Too cold
Fig. 13.2: Schematic of greenhouse 
effect on Earth
Chapter 13.indd   214 Chapter 13.indd   214 6/28/2025   6:15:45 PM 6/28/2025   6:15:45 PM