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Looking for NCERT Class 11 Geography Fundamentals of Geography Chapter 7 Composition and Structure of Atmosphere Notes? You’re in the right place! This blog gives you simple and clear notes that make it easy to understand the key concepts of this chapter. Whether you’re preparing for your exams or just want a quick revision, these notes will help you grasp the essential ideas without going through the entire textbook. Let’s dive in!
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Explore Notes of Class 11 Fundamentals of Geography
Introduction
The atmosphere is a layer of gases that surrounds the Earth. It is held close to the planet by the force of gravity. The atmosphere is extremely important for life on Earth. It gives us oxygen to breathe, carbon dioxide for plants to make food, and keeps the Earth warm by trapping heat. It also protects us from harmful ultraviolet rays coming from the Sun.
Also Read:
- NCERT Solutions and Notes for Class 7 Geography Chapter 7: Life in the Deserts (Free PDF)
- NCERT Class 7 Geography Chapter 3 ‘Our Changing Earth’: Notes and Solutions (Free PDF)
Composition of the Atmosphere
The atmosphere is made up of gases, water vapour, and dust particles. All these components play important roles in maintaining the Earth’s climate and weather systems.
1. Gases in the Atmosphere
There are many gases in the atmosphere, but only a few are present in large amounts. The most important gases are:
- Nitrogen (78.08%): This is the most abundant gas. It does not react easily and helps plants grow when converted into useful compounds by soil bacteria.
- Oxygen (20.95%): This gas is essential for all living beings as we need it to breathe. It is also necessary for things to burn.
- Argon (0.93%): This is a noble gas and does not participate in any reactions. It has no major role in weather or climate.
- Carbon Dioxide (0.03%): Although present in a small amount, this gas is very important. Plants use it to make their food through photosynthesis. It also helps trap heat in the atmosphere and keeps the Earth warm.
- Ozone (O₃): Found in the upper part of the atmosphere, ozone forms a layer that absorbs the Sun’s harmful ultraviolet rays.
Other gases like neon, helium, krypton, and xenon are present in very small amounts and do not affect the weather or climate much. As we go higher up in the atmosphere, the amount of these gases starts to change. Oxygen becomes very low around 120 km, and gases like carbon dioxide and water vapour are mostly found below 90 km.
2. Water Vapour
Water vapour is the gaseous form of water present in the air. It varies from place to place. In warm and humid places, water vapour can make up to 4% of the air, while in cold or dry places, it can be less than 1%.
- Water vapour is very important because it:
- Absorbs heat from the Sun and Earth, helping to keep the planet warm.
- Is responsible for the formation of clouds, fog, rain, and snow.
- Plays a role in the energy balance of the Earth by trapping heat.
- Water vapour also affects how stable or unstable the air is, which impacts weather patterns.
3. Dust Particles
Dust particles come from various sources like soil, ash from volcanoes, sea salt, smoke, pollen, and even space (from meteors). These particles are mostly found in the lower part of the atmosphere. They help in:
- Forming clouds by acting as a surface on which water droplets can condense.
- Scattering sunlight, which makes the sky appear red during sunrise and sunset.
- There are more dust particles in dry regions than in humid or rainy areas.
Structure of the Atmosphere
The atmosphere is divided into different layers based on how temperature changes with height. Each layer has its own features and plays a unique role. The five main layers of the atmosphere (from bottom to top) are:
1. Troposphere: The troposphere is the lowest layer of the atmosphere and is the one in which we live. It stretches up to:
- About 8 km at the poles.
- Around 18 km at the equator.
All weather changes like clouds, rainfall, storms, and winds happen in this layer. It contains almost all the water vapour, dust, and gases that we need for life. As we go higher in this layer, the temperature decreases at a rate of 6.5°C per 1,000 meters. This layer is also the most important for all living things.
Tropopause: This is the boundary between the troposphere and the next layer. Here, the temperature stops decreasing and becomes stable. At the equator, the temperature at the tropopause is around -80°C.
2. Stratosphere: Above the tropopause lies the stratosphere, which extends up to 50 km above the Earth. This layer contains the ozone layer, which protects life on Earth by blocking the Sun’s harmful ultraviolet rays. The temperature increases with height in this layer because of the heat absorbed by ozone. There is very little weather in this layer, which is why it is ideal for flying airplanes.
Stratopause: The top limit of the stratosphere. It separates the stratosphere from the next layer.
3. Mesosphere: The mesosphere lies above the stratosphere and goes up to 80 km. In this layer, the temperature decreases again as we go higher, making it the coldest part of the atmosphere.Meteors or shooting stars burn up in this layer due to friction with air.
Mesopause: The boundary at the top of the mesosphere. It marks the transition to the next layer.
4. Thermosphere: The thermosphere starts above the mesopause and extends up to 400 km. The temperature here rises sharply with height because this layer absorbs a lot of solar energy. This layer contains the ionosphere, which has electrically charged particles. These particles reflect radio waves, making long-distance radio communication possible. Also, beautiful light displays called auroras (Northern and Southern Lights) are seen in this layer.
5. Exosphere: The exosphere is the uppermost layer of the atmosphere. It starts above 400 km and gradually merges with outer space. The air here is extremely thin and mostly contains light gases like hydrogen and helium. Satellites orbit the Earth in this layer.
Weather and Climate Elements
The atmosphere controls the Earth’s weather and climate through several important elements:
- Temperature: Measures how hot or cold the air is.
- Air Pressure: The weight of air pressing down on the Earth.
- Wind: Air moving from high pressure to low pressure.
- Humidity: Amount of water vapour in the air.
- Clouds: Formed when water vapour condenses.
- Precipitation: Any form of water that falls from the sky like rain, snow, hail, etc.
These elements are constantly changing and affect daily weather and long-term climate.
Also Read:
- NCERT Solutions and Notes for Class 7 Geography Chapter 5: Water (Free PDF)
- NCERT Class 7 Geography Chapter 4 ‘Air’: Notes and Solutions (Free PDF)
Important Definition in NCERT Notes Class 11 Geography Fundamentals of Geography Chapter 7 Composition and Structure of Atmosphere
This chapter explains the Earth’s atmosphere: its layers, the gases in it, and what it’s made of. To help you revise easily, here are some important words from the chapter explained in simple language.
- Atmosphere: The layer of gases surrounding the Earth that protects life and controls temperature.
- Composition of Atmosphere: Made up of gases, water vapor, and dust particles. Main gases are nitrogen (78%), oxygen (21%), and others.
- Permanent Gases: Gases that remain constant in amount, like nitrogen, oxygen, and argon.
- Variable Gases: Gases whose amounts change with time and place, such as carbon dioxide, water vapor, ozone, and methane.
- Dust Particles: Tiny solid particles like pollen, smoke, and salt that help form clouds and scatter sunlight.
- Ozone Layer: A layer in the stratosphere that absorbs harmful UV rays from the Sun, protecting life on Earth.
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FAQs
The atmosphere is the layer of gases surrounding the Earth. It is important because it provides oxygen to breathe, protects us from harmful solar radiation, traps heat to keep the Earth warm, and supports weather and climate systems.
The atmosphere mainly consists of nitrogen (78%), oxygen (21%), argon (0.93%), and small amounts of carbon dioxide, ozone, and other gases. Nitrogen and oxygen are the most abundant and important for life.
The ozone layer, located in the stratosphere, absorbs the Sun’s harmful ultraviolet (UV) rays, protecting living organisms on Earth from damage.
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