Selina Textbook Solutions: Composition and Structure of the Atmosphere | Geography Class 7 ICSE PDF Download

 Page 1


Composition and Structure of the Atmosphere 
Discuss 
Question  
Discuss the importance of the different layers of the atmosphere ? 
Answer: 
The earth is the only planet in the universe that has life. One of the reasons why life 
exists on this planet is an encompassing blanket of gases called the atmosphere. It is 
like a blanket of air that protects the earth from the harmful rays of the sun. It also 
controls the temperature and, most important of all, it contains oxygen, which is 
essential for every form of life. This almost invisible blanket is kept intact around the 
planet by another invisible entity called gravity. 
THINK AND ANSWER 
Question  
What would happen to the earth if the atmosphere disappeared ? 
Answer: 
If you would like to see what the earth would look like, take a look at the moon, with all 
its craters. Another thing that would happen if the earth had no atmosphere is the 
oceans would boil away, leaving no water here on earth because there is not 
atmosphere to help complete the water cycle. 
VALUES AND LIFE SKILLS 
Question  
We often leave the lights switched on and fans running when we are not in the room. 
We switch on the air-conditioning even though we don’t really need it. We insist on 
being dropped to school in the car every day. Thus, we waste valuable energy which is 
generally produced by burning coal and petroleum. As you know, the burning of these 
fuels release gases that pollute the atmosphere. 
Make a list of the similar things that we do without realizing that we are destroying the 
environment. Think of the ways that we can behave differently. 
Answer: 
The list of the similar things that we do without realizing that we are destroying our 
environment and the ways that we can behave differently and save are : 
1. Leaving The Lights On : 
You’ve probably heard this a million times before but turning the light off when you 
leave the room, even if you’re only going for a few minutes, really does make a 
difference to the environment, since it saves a finite source of energy that can’t be 
replaced. 
Page 2


Composition and Structure of the Atmosphere 
Discuss 
Question  
Discuss the importance of the different layers of the atmosphere ? 
Answer: 
The earth is the only planet in the universe that has life. One of the reasons why life 
exists on this planet is an encompassing blanket of gases called the atmosphere. It is 
like a blanket of air that protects the earth from the harmful rays of the sun. It also 
controls the temperature and, most important of all, it contains oxygen, which is 
essential for every form of life. This almost invisible blanket is kept intact around the 
planet by another invisible entity called gravity. 
THINK AND ANSWER 
Question  
What would happen to the earth if the atmosphere disappeared ? 
Answer: 
If you would like to see what the earth would look like, take a look at the moon, with all 
its craters. Another thing that would happen if the earth had no atmosphere is the 
oceans would boil away, leaving no water here on earth because there is not 
atmosphere to help complete the water cycle. 
VALUES AND LIFE SKILLS 
Question  
We often leave the lights switched on and fans running when we are not in the room. 
We switch on the air-conditioning even though we don’t really need it. We insist on 
being dropped to school in the car every day. Thus, we waste valuable energy which is 
generally produced by burning coal and petroleum. As you know, the burning of these 
fuels release gases that pollute the atmosphere. 
Make a list of the similar things that we do without realizing that we are destroying the 
environment. Think of the ways that we can behave differently. 
Answer: 
The list of the similar things that we do without realizing that we are destroying our 
environment and the ways that we can behave differently and save are : 
1. Leaving The Lights On : 
You’ve probably heard this a million times before but turning the light off when you 
leave the room, even if you’re only going for a few minutes, really does make a 
difference to the environment, since it saves a finite source of energy that can’t be 
replaced. 
2. Boiling The Kettle : 
Many people guess the amount of water they need when they boil the kettle, and 
they end up boiling too much. Boiling a kettle actually uses a lot of power- enough 
to light a whole household- which also costs the householder money. There are 
energy efficient kettles available that can help to reduce energy usage, and kettles 
that measure how much water is needed for a single mug or a pot of tea. 
3. Eating Farmed Meat : 
Maybe you’re not ready to take a step in the veggie or vegan direction, but if 
you’re eating farmed meat, you’re supporting an incredibly environmentally 
damaging industry. Many acres of rainforest are cleared to grow soy crops and 
grains to feed cattle, and overgrazing of cattle is a major reason for global soil 
depletion and source of climate pollution. 
4. Commuting : 
Whether you’re flying away on business trips or commuting to work on a daily 
basis, the way we travel is one of the biggest environmental polluters in our lives. 
You may not be able to 
give up these habits, but taking steps to reduce them will impact the environment, 
local pollution levels, and your health. 
5. Wasting Paper : 
We live in a world of mass paper usage, where recycling can easily ease an 
otherwise guilty conscience and prompt even the most devoted re-users to waste 
paper. We may all be guilty of throwing away pieces of paper that could otherwise 
be reused at least once, if only for note-taking purposes and to-do lists, but it’s 
easy to forget that recycling still uses energy, which can be reduced if you decide 
to reuse. 
6. Leaving The Tap Running : 
Whether you’re washing the dishes or brushing your teeth, leaving the tap running 
while you do so wastes a vast amount of water. It may seem like a small water 
saving, but soaking dishes before washing them and turning off the faucet while 
you brush your teeth really does reduce the amount of water you use. 
7. Using Plastic Bags : 
It’s hard to make the connection between the single plastic bag you get at the 
grocery store once a week, and the Great Pacific Garbage Patch. However, there 
is a strong likelihood that the plastic bags you bring home end will end up in the 
ocean, or worse. Consider buy a cloth bag instead and make a habit of keeping it 
in your pocket or bag. 
EXERCISES 
A. Fill in the blanks. 
1. 78% per cent of the atmosphere is made of nitrogen. 
2. Along with carbon dioxide and methane, water vapour is a potent greenhouse gas. 
3. The rate at which the temperature drops in the troposphere is 1°C per 165 metres. 
4. The thermosphere is the layer of the atmosphere that help in radio transmission. 
5. The upper part of the thermosphere is called the ionosphere. 
Page 3


Composition and Structure of the Atmosphere 
Discuss 
Question  
Discuss the importance of the different layers of the atmosphere ? 
Answer: 
The earth is the only planet in the universe that has life. One of the reasons why life 
exists on this planet is an encompassing blanket of gases called the atmosphere. It is 
like a blanket of air that protects the earth from the harmful rays of the sun. It also 
controls the temperature and, most important of all, it contains oxygen, which is 
essential for every form of life. This almost invisible blanket is kept intact around the 
planet by another invisible entity called gravity. 
THINK AND ANSWER 
Question  
What would happen to the earth if the atmosphere disappeared ? 
Answer: 
If you would like to see what the earth would look like, take a look at the moon, with all 
its craters. Another thing that would happen if the earth had no atmosphere is the 
oceans would boil away, leaving no water here on earth because there is not 
atmosphere to help complete the water cycle. 
VALUES AND LIFE SKILLS 
Question  
We often leave the lights switched on and fans running when we are not in the room. 
We switch on the air-conditioning even though we don’t really need it. We insist on 
being dropped to school in the car every day. Thus, we waste valuable energy which is 
generally produced by burning coal and petroleum. As you know, the burning of these 
fuels release gases that pollute the atmosphere. 
Make a list of the similar things that we do without realizing that we are destroying the 
environment. Think of the ways that we can behave differently. 
Answer: 
The list of the similar things that we do without realizing that we are destroying our 
environment and the ways that we can behave differently and save are : 
1. Leaving The Lights On : 
You’ve probably heard this a million times before but turning the light off when you 
leave the room, even if you’re only going for a few minutes, really does make a 
difference to the environment, since it saves a finite source of energy that can’t be 
replaced. 
2. Boiling The Kettle : 
Many people guess the amount of water they need when they boil the kettle, and 
they end up boiling too much. Boiling a kettle actually uses a lot of power- enough 
to light a whole household- which also costs the householder money. There are 
energy efficient kettles available that can help to reduce energy usage, and kettles 
that measure how much water is needed for a single mug or a pot of tea. 
3. Eating Farmed Meat : 
Maybe you’re not ready to take a step in the veggie or vegan direction, but if 
you’re eating farmed meat, you’re supporting an incredibly environmentally 
damaging industry. Many acres of rainforest are cleared to grow soy crops and 
grains to feed cattle, and overgrazing of cattle is a major reason for global soil 
depletion and source of climate pollution. 
4. Commuting : 
Whether you’re flying away on business trips or commuting to work on a daily 
basis, the way we travel is one of the biggest environmental polluters in our lives. 
You may not be able to 
give up these habits, but taking steps to reduce them will impact the environment, 
local pollution levels, and your health. 
5. Wasting Paper : 
We live in a world of mass paper usage, where recycling can easily ease an 
otherwise guilty conscience and prompt even the most devoted re-users to waste 
paper. We may all be guilty of throwing away pieces of paper that could otherwise 
be reused at least once, if only for note-taking purposes and to-do lists, but it’s 
easy to forget that recycling still uses energy, which can be reduced if you decide 
to reuse. 
6. Leaving The Tap Running : 
Whether you’re washing the dishes or brushing your teeth, leaving the tap running 
while you do so wastes a vast amount of water. It may seem like a small water 
saving, but soaking dishes before washing them and turning off the faucet while 
you brush your teeth really does reduce the amount of water you use. 
7. Using Plastic Bags : 
It’s hard to make the connection between the single plastic bag you get at the 
grocery store once a week, and the Great Pacific Garbage Patch. However, there 
is a strong likelihood that the plastic bags you bring home end will end up in the 
ocean, or worse. Consider buy a cloth bag instead and make a habit of keeping it 
in your pocket or bag. 
EXERCISES 
A. Fill in the blanks. 
1. 78% per cent of the atmosphere is made of nitrogen. 
2. Along with carbon dioxide and methane, water vapour is a potent greenhouse gas. 
3. The rate at which the temperature drops in the troposphere is 1°C per 165 metres. 
4. The thermosphere is the layer of the atmosphere that help in radio transmission. 
5. The upper part of the thermosphere is called the ionosphere. 
B. Match the following. 
 
 
Answer: 
 
 
C. Choose the correct answer. 
1. This per cent of the atmosphere is composed of nitrogen. 
1. 99 
2. 78 
3. 21 
4. 76 
2. 21 per cent of the atmosphere is composed of 
1. Helium 
2. Oxygen 
3. Nitrogen 
4. Hydrogen 
3. This gas protects us from the harmful ultraviolet radiation. 
1. Oxygen 
2. Ozone 
Page 4


Composition and Structure of the Atmosphere 
Discuss 
Question  
Discuss the importance of the different layers of the atmosphere ? 
Answer: 
The earth is the only planet in the universe that has life. One of the reasons why life 
exists on this planet is an encompassing blanket of gases called the atmosphere. It is 
like a blanket of air that protects the earth from the harmful rays of the sun. It also 
controls the temperature and, most important of all, it contains oxygen, which is 
essential for every form of life. This almost invisible blanket is kept intact around the 
planet by another invisible entity called gravity. 
THINK AND ANSWER 
Question  
What would happen to the earth if the atmosphere disappeared ? 
Answer: 
If you would like to see what the earth would look like, take a look at the moon, with all 
its craters. Another thing that would happen if the earth had no atmosphere is the 
oceans would boil away, leaving no water here on earth because there is not 
atmosphere to help complete the water cycle. 
VALUES AND LIFE SKILLS 
Question  
We often leave the lights switched on and fans running when we are not in the room. 
We switch on the air-conditioning even though we don’t really need it. We insist on 
being dropped to school in the car every day. Thus, we waste valuable energy which is 
generally produced by burning coal and petroleum. As you know, the burning of these 
fuels release gases that pollute the atmosphere. 
Make a list of the similar things that we do without realizing that we are destroying the 
environment. Think of the ways that we can behave differently. 
Answer: 
The list of the similar things that we do without realizing that we are destroying our 
environment and the ways that we can behave differently and save are : 
1. Leaving The Lights On : 
You’ve probably heard this a million times before but turning the light off when you 
leave the room, even if you’re only going for a few minutes, really does make a 
difference to the environment, since it saves a finite source of energy that can’t be 
replaced. 
2. Boiling The Kettle : 
Many people guess the amount of water they need when they boil the kettle, and 
they end up boiling too much. Boiling a kettle actually uses a lot of power- enough 
to light a whole household- which also costs the householder money. There are 
energy efficient kettles available that can help to reduce energy usage, and kettles 
that measure how much water is needed for a single mug or a pot of tea. 
3. Eating Farmed Meat : 
Maybe you’re not ready to take a step in the veggie or vegan direction, but if 
you’re eating farmed meat, you’re supporting an incredibly environmentally 
damaging industry. Many acres of rainforest are cleared to grow soy crops and 
grains to feed cattle, and overgrazing of cattle is a major reason for global soil 
depletion and source of climate pollution. 
4. Commuting : 
Whether you’re flying away on business trips or commuting to work on a daily 
basis, the way we travel is one of the biggest environmental polluters in our lives. 
You may not be able to 
give up these habits, but taking steps to reduce them will impact the environment, 
local pollution levels, and your health. 
5. Wasting Paper : 
We live in a world of mass paper usage, where recycling can easily ease an 
otherwise guilty conscience and prompt even the most devoted re-users to waste 
paper. We may all be guilty of throwing away pieces of paper that could otherwise 
be reused at least once, if only for note-taking purposes and to-do lists, but it’s 
easy to forget that recycling still uses energy, which can be reduced if you decide 
to reuse. 
6. Leaving The Tap Running : 
Whether you’re washing the dishes or brushing your teeth, leaving the tap running 
while you do so wastes a vast amount of water. It may seem like a small water 
saving, but soaking dishes before washing them and turning off the faucet while 
you brush your teeth really does reduce the amount of water you use. 
7. Using Plastic Bags : 
It’s hard to make the connection between the single plastic bag you get at the 
grocery store once a week, and the Great Pacific Garbage Patch. However, there 
is a strong likelihood that the plastic bags you bring home end will end up in the 
ocean, or worse. Consider buy a cloth bag instead and make a habit of keeping it 
in your pocket or bag. 
EXERCISES 
A. Fill in the blanks. 
1. 78% per cent of the atmosphere is made of nitrogen. 
2. Along with carbon dioxide and methane, water vapour is a potent greenhouse gas. 
3. The rate at which the temperature drops in the troposphere is 1°C per 165 metres. 
4. The thermosphere is the layer of the atmosphere that help in radio transmission. 
5. The upper part of the thermosphere is called the ionosphere. 
B. Match the following. 
 
 
Answer: 
 
 
C. Choose the correct answer. 
1. This per cent of the atmosphere is composed of nitrogen. 
1. 99 
2. 78 
3. 21 
4. 76 
2. 21 per cent of the atmosphere is composed of 
1. Helium 
2. Oxygen 
3. Nitrogen 
4. Hydrogen 
3. This gas protects us from the harmful ultraviolet radiation. 
1. Oxygen 
2. Ozone 
3. Helium 
4. Hydrogen 
4. The rate at which the temperature drops in the troposphere is called 
1. lapse rate 
2. loss rate 
3. less rate 
4. drop rate 
5. This layer of the atmosphere has the lowest temperature. 
1. Mesosphere 
2. Thermosphere 
3. Tropopause 
4. Stratosphere 
D. State whether the following are true or false. 
1. The earth’s atmosphere contains 99 per cent oxygen, which is essential for life. 
Answer.  False. 
Correct : The earth’s atmosphere contains 21% per cent oxygen, which is essential for 
life. 
2. The stratosphere is the lowest layer of the atmosphere. 
Answer. False. 
Correct : The troposphere is the lowest layer of the atmosphere. 
3. The temperature drops at the rate of 1°C per 185 metres in the atmosphere. 
Answer. False. 
Correct : The temperature drops at the rate of 1°C per 165 metres in the atmosphere. 
4. The stratosphere extends from the top of the troposphere up to 80 km above the 
surface of the earth. 
Answer. False. 
Correct : The stratosphere extends from the top of the troposphere up to 50 km above 
the surface of the earth. 
5. Communication satellites orbit in thermosphere. 
Answer. True. 
 
Page 5


Composition and Structure of the Atmosphere 
Discuss 
Question  
Discuss the importance of the different layers of the atmosphere ? 
Answer: 
The earth is the only planet in the universe that has life. One of the reasons why life 
exists on this planet is an encompassing blanket of gases called the atmosphere. It is 
like a blanket of air that protects the earth from the harmful rays of the sun. It also 
controls the temperature and, most important of all, it contains oxygen, which is 
essential for every form of life. This almost invisible blanket is kept intact around the 
planet by another invisible entity called gravity. 
THINK AND ANSWER 
Question  
What would happen to the earth if the atmosphere disappeared ? 
Answer: 
If you would like to see what the earth would look like, take a look at the moon, with all 
its craters. Another thing that would happen if the earth had no atmosphere is the 
oceans would boil away, leaving no water here on earth because there is not 
atmosphere to help complete the water cycle. 
VALUES AND LIFE SKILLS 
Question  
We often leave the lights switched on and fans running when we are not in the room. 
We switch on the air-conditioning even though we don’t really need it. We insist on 
being dropped to school in the car every day. Thus, we waste valuable energy which is 
generally produced by burning coal and petroleum. As you know, the burning of these 
fuels release gases that pollute the atmosphere. 
Make a list of the similar things that we do without realizing that we are destroying the 
environment. Think of the ways that we can behave differently. 
Answer: 
The list of the similar things that we do without realizing that we are destroying our 
environment and the ways that we can behave differently and save are : 
1. Leaving The Lights On : 
You’ve probably heard this a million times before but turning the light off when you 
leave the room, even if you’re only going for a few minutes, really does make a 
difference to the environment, since it saves a finite source of energy that can’t be 
replaced. 
2. Boiling The Kettle : 
Many people guess the amount of water they need when they boil the kettle, and 
they end up boiling too much. Boiling a kettle actually uses a lot of power- enough 
to light a whole household- which also costs the householder money. There are 
energy efficient kettles available that can help to reduce energy usage, and kettles 
that measure how much water is needed for a single mug or a pot of tea. 
3. Eating Farmed Meat : 
Maybe you’re not ready to take a step in the veggie or vegan direction, but if 
you’re eating farmed meat, you’re supporting an incredibly environmentally 
damaging industry. Many acres of rainforest are cleared to grow soy crops and 
grains to feed cattle, and overgrazing of cattle is a major reason for global soil 
depletion and source of climate pollution. 
4. Commuting : 
Whether you’re flying away on business trips or commuting to work on a daily 
basis, the way we travel is one of the biggest environmental polluters in our lives. 
You may not be able to 
give up these habits, but taking steps to reduce them will impact the environment, 
local pollution levels, and your health. 
5. Wasting Paper : 
We live in a world of mass paper usage, where recycling can easily ease an 
otherwise guilty conscience and prompt even the most devoted re-users to waste 
paper. We may all be guilty of throwing away pieces of paper that could otherwise 
be reused at least once, if only for note-taking purposes and to-do lists, but it’s 
easy to forget that recycling still uses energy, which can be reduced if you decide 
to reuse. 
6. Leaving The Tap Running : 
Whether you’re washing the dishes or brushing your teeth, leaving the tap running 
while you do so wastes a vast amount of water. It may seem like a small water 
saving, but soaking dishes before washing them and turning off the faucet while 
you brush your teeth really does reduce the amount of water you use. 
7. Using Plastic Bags : 
It’s hard to make the connection between the single plastic bag you get at the 
grocery store once a week, and the Great Pacific Garbage Patch. However, there 
is a strong likelihood that the plastic bags you bring home end will end up in the 
ocean, or worse. Consider buy a cloth bag instead and make a habit of keeping it 
in your pocket or bag. 
EXERCISES 
A. Fill in the blanks. 
1. 78% per cent of the atmosphere is made of nitrogen. 
2. Along with carbon dioxide and methane, water vapour is a potent greenhouse gas. 
3. The rate at which the temperature drops in the troposphere is 1°C per 165 metres. 
4. The thermosphere is the layer of the atmosphere that help in radio transmission. 
5. The upper part of the thermosphere is called the ionosphere. 
B. Match the following. 
 
 
Answer: 
 
 
C. Choose the correct answer. 
1. This per cent of the atmosphere is composed of nitrogen. 
1. 99 
2. 78 
3. 21 
4. 76 
2. 21 per cent of the atmosphere is composed of 
1. Helium 
2. Oxygen 
3. Nitrogen 
4. Hydrogen 
3. This gas protects us from the harmful ultraviolet radiation. 
1. Oxygen 
2. Ozone 
3. Helium 
4. Hydrogen 
4. The rate at which the temperature drops in the troposphere is called 
1. lapse rate 
2. loss rate 
3. less rate 
4. drop rate 
5. This layer of the atmosphere has the lowest temperature. 
1. Mesosphere 
2. Thermosphere 
3. Tropopause 
4. Stratosphere 
D. State whether the following are true or false. 
1. The earth’s atmosphere contains 99 per cent oxygen, which is essential for life. 
Answer.  False. 
Correct : The earth’s atmosphere contains 21% per cent oxygen, which is essential for 
life. 
2. The stratosphere is the lowest layer of the atmosphere. 
Answer. False. 
Correct : The troposphere is the lowest layer of the atmosphere. 
3. The temperature drops at the rate of 1°C per 185 metres in the atmosphere. 
Answer. False. 
Correct : The temperature drops at the rate of 1°C per 165 metres in the atmosphere. 
4. The stratosphere extends from the top of the troposphere up to 80 km above the 
surface of the earth. 
Answer. False. 
Correct : The stratosphere extends from the top of the troposphere up to 50 km above 
the surface of the earth. 
5. Communication satellites orbit in thermosphere. 
Answer. True. 
 
E. Answer the following questions in brief. 
Question 1. 
How is the atmosphere kept in place around the earth? 
Answer: 
The atmosphere is kept in place around the planet by another invisible entity called 
gravity. 
Question 2. 
Name the important gases that are found in the atmosphere. 
Answer: 
The important gases that are found in atmosphere are nitrogen, oxygen, carbon-dioxide, 
hydrogen, helium and argon. 
Question 3. 
How is carbon dioxide a useful gas for life on earth? 
Answer: 
Carbon dioxide exists in the earth’s atmosphere as a colourless 
and odourless gas. Carbon dioxide is produced by all animals, fungi and 
microorganisms during respiration and is used by plants during photosynthesis. It is also 
useful gas as it creates the greenhouse effect. It would have been too cold for life to 
exist on this planet without greenhouse effect. 
Question 4. 
What is the troposphere? 
Answer: 
Troposphere is the lowest layer of the atmosphere. It protects us from the heat of sun 
during day and keeps the earth warm at night ozone. This is the densest layer of the 
atmosphere and its thickness varies from 8 km over the poles to 18 km over the 
equator. 
Question 5. 
What is the difference between the troposphere and the tropopause? 
Answer: 
The lowest layer of atmosphere is called troposphere where as the boundary between 
the troposphere and the stratosphere is called tropopause. 
F. Answer the following questions in one or two paragraphs. 
Question 1. 
Write briefly about the layers of the atmosphere. 
Answer: 
The atmosphere is divided into five layers starting from the Earth’s surface