CBSE Class 7 Social Science Our Environment NCERT Solutions Chapter 4: Air
This chapter delves into the composition and importance of the air surrounding our planet. It explains the structure of the Earth's atmosphere, detailing its distinct layers: the Troposphere, Stratosphere (including the vital ozone layer), Mesosphere, Thermosphere, and Exosphere. The solutions highlight the primary gases that constitute the atmosphere, namely Nitrogen and Oxygen, and their respective percentages. Furthermore, the chapter addresses the concept of the greenhouse effect, identifying Carbon Dioxide as a key contributing gas. It also defines weather as the hour-to-hour atmospheric conditions and distinguishes it from climate. These NCERT Solutions provide clear, step-by-step explanations to help students grasp fundamental concepts related to air and its role in our environment, aiding in effective exam revision.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 7 |
| Subject | Social Science Our Environment |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 4 |
Chapter summary
Chapter 4 of CBSE Class 7 Social Science, 'Air', focuses on the Earth's atmosphere. The NCERT Solutions cover the definition and layered structure of the atmosphere (Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere), the major gases like Nitrogen and Oxygen, and the role of Carbon Dioxide in the greenhouse effect. It also clarifies the concept of weather. These solutions are designed to help students understand the basic components and phenomena related to the air around us.
Learning outcomes
- Understand the definition and composition of the Earth's atmosphere.
- Identify and describe the different layers of the atmosphere.
- Recognize the primary gases that make up the atmosphere and their proportions.
- Explain the concept of the greenhouse effect and the role of Carbon Dioxide.
- Differentiate between weather and climate.
Topics covered
Paper topics
- Atmosphere definition
- Layers of the atmosphere
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
- Composition of atmosphere
- Nitrogen
- Oxygen
- Greenhouse effect
- Weather
Important topics
- Layers of the atmosphere
- Composition of atmosphere
- Greenhouse effect
- Weather vs. Climate
PDF preview
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Questions and Solutions
Question 1(A)
The atmosphere is defined as the thick blanket of air that envelops the surface of the Earth. This gaseous layer is crucial for life as we know it. It is structured into several distinct layers, each with unique characteristics:
- Troposphere: This is the lowest layer, situated directly above the Earth's surface. It is where the air we breathe is found, making it essential for supporting life on our planet.
- Stratosphere: Located above the Troposphere, this layer extends up to approximately 50 km. It is significant because it contains the ozone layer, which absorbs harmful ultraviolet radiation from the sun. Airplanes often fly in this layer due to its stability.
- Mesosphere: This is the third layer, situated above the Stratosphere and extending up to about 80 km. It is known for its role in burning up most meteorites that enter the Earth's atmosphere, protecting the surface from impacts.
- Thermosphere: In this layer, the temperature increases rapidly with altitude. The Ionosphere, which plays a vital role in radio wave transmission, is a part of the Thermosphere.
- Exosphere: This is the outermost layer of the atmosphere, gradually fading into outer space. The air in the Exosphere is extremely thin.
Question 1(B)
The two primary gases that constitute the vast majority of the Earth's atmosphere are:
- Nitrogen: This gas is the most abundant, occupying approximately 78% of the air around us.
- Oxygen: This gas is the second most abundant, making up about 21% of the atmosphere. It is essential for respiration for most living organisms.
Question 1(C)
Carbon dioxide is a significant gas responsible for creating the greenhouse effect in the atmosphere. Along with other greenhouse gases like methane and carbon monoxide, it traps heat radiated from the Earth's surface, contributing to the warming of the planet.
Question 1(D)
Weather refers to the state of the atmosphere at a particular place and time, characterized by conditions that can change rapidly. These atmospheric conditions, such as temperature, humidity, precipitation, and wind, can vary from hour to hour and day to day. A long-term record of these changing atmospheric conditions over an extended period helps determine the climate of a region, which is distinct from the day-to-day weather.
Common mistakes
- Confusing weather with climate.
- Not clearly distinguishing between the different atmospheric layers and their characteristics.
- Underestimating the importance of specific gases like Carbon Dioxide in atmospheric processes.
Revision tips
- Draw and label the different layers of the atmosphere to aid memorization.
- Create flashcards for key terms like 'atmosphere', 'weather', and 'greenhouse effect'.
- Practice explaining the role of Nitrogen and Oxygen in the atmosphere.
- Review the definition of weather and how it differs from climate.
Practice MCQs
Q1. What is the primary function of the Stratosphere mentioned in the text?
Explanation: The Stratosphere is identified as the layer where airplanes fly and contains the crucial ozone layer, which protects us from harmful UV radiation.
Q2. Which gas is primarily responsible for the greenhouse effect according to the provided solutions?
Explanation: Carbon Dioxide is highlighted as a major contributor to the greenhouse effect, trapping heat in the atmosphere.
Q3. What percentage of the atmosphere is occupied by Nitrogen?
Explanation: Nitrogen is the most abundant gas in the atmosphere, making up approximately 78% of the air.
Q4. Which layer of the atmosphere is closest to the Earth's surface and supports life?
Explanation: The Troposphere is the lowest layer of the atmosphere, containing the air we breathe and supporting life on Earth.
Q5. How is weather described in the context of atmospheric conditions?
Explanation: Weather refers to the atmospheric conditions that change frequently, even hour-to-hour or day-to-day.
Frequently asked questions
What is the atmosphere?
The atmosphere is the thick blanket of air that surrounds the Earth's surface, composed of various gases and divided into distinct layers.
What are the main gases in the Earth's atmosphere?
The two main gases that make up the bulk of the atmosphere are Nitrogen (about 78%) and Oxygen (about 21%).
Which layer of the atmosphere contains the ozone layer?
The ozone layer is located in the Stratosphere, which is above the Troposphere.
What causes the greenhouse effect?
Carbon Dioxide, along with other gases, contributes to the greenhouse effect by trapping heat in the atmosphere.
How is weather different from climate?
Weather refers to the short-term, hour-to-hour atmospheric conditions, while climate is the long-term average of these conditions over a period.
Where do meteorites burn up when entering Earth's atmosphere?
Meteorites typically burn up in the Mesosphere, which is the third layer of the atmosphere.
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