Chapter – 7

Composition and Structure of Atmosphere

In this post we have given the detailed notes of class 11 Geography Book 1 Chapter 7 (Composition and Structure of Atmosphere) in English. These notes are useful for the students who are going to appear in class 11 board exams.

Printed Books Are Available Now!

Chapter 7: Composition and Structure of Atmosphere

Introduction

• The atmosphere is a mixture of different gases and it envelopes the Earth all round.  
• Air is essential to the survival of all organisms.  
• Some organisms like humans may survive for some time without food and water but can’t survive even a few minutes without breathing air.  
• The atmosphere contains life-giving gases like oxygen for humans and animals and carbon dioxide for plants.  

Composition of the Atmosphere

• The atmosphere is composed of gases, water vapor, and dust particles.  
• The proportion of gases changes in the higher layers of the atmosphere.  

Gases

• Nitrogen and oxygen are the major gases in the atmosphere.  
• The volume of other gases is constant but the volume of carbon dioxide has been rising in the past few decades mainly because of the burning of fossil fuels.  
• Carbon dioxide is meteorologically a very important gas.  
• It is transparent to the incoming solar radiation but opaque to the outgoing terrestrial radiation.  
• It absorbs a part of terrestrial radiation and reflects back some part of it towards the Earth’s surface.
• It is largely responsible for the greenhouse effect.  
• The rising volume of carbon dioxide has also increased the temperature of the air.  
• Ozone is another important component of the atmosphere found between 10 and 50 km above the Earth’s surface.  
• It acts as a filter and absorbs the ultraviolet rays radiating from the sun and prevents them from reaching the surface of the Earth.  

Water Vapor

• Water vapor is also a variable gas in the atmosphere, which decreases with altitude.  
• Water vapor also decreases from the equator towards the poles.  
• It absorbs parts of the insolation from the sun and preserves the Earth’s radiated heat.  
• It thus acts like a blanket allowing the Earth neither to become too cold nor too hot.  
• Water vapor also contributes to the stability and instability in the air.  

Dust Particles

• The atmosphere has a sufficient capacity to keep small solid particles, which may originate from different sources like sea salts, fine soil, smoke-soot, ash, pollen, dust, and disintegrated particles of meteors.  
• Dust particles are generally concentrated in the lower layers of the atmosphere.  
• Convectional air currents may transport them to great heights.  
• The higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and polar regions.  
• Dust and salt particles act as hygroscopic nuclei around which water vapor condenses to produce clouds.  

Structure of the Atmosphere

• The atmosphere consists of different layers with varying density and temperature.  
• Density is highest near the surface of the Earth and decreases with increasing altitude.  
• The column of atmosphere is divided into five different layers depending upon the temperature condition.  
• They are: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.  

Troposphere

• The troposphere is the lowermost layer of the atmosphere.  
• Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.  
• Thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convectional currents.  
• This layer contains dust particles and water vapor.  
• All changes in climate and weather take place in this layer.  
• The temperature in this layer decreases at the rate of 1°C for every 165m of height.  
• This is the most important layer for all biological activity.  

Tropopause

• The zone separating the troposphere from the stratosphere is known as the tropopause.  
• The air temperature at the tropopause is about -80°C over the equator and about -45°C over the poles.  
• The temperature here is nearly constant, and hence, it is called the tropopause.  

Stratosphere

• The stratosphere is found above the tropopause and extends up to a height of 50 km.  
• One important feature of the stratosphere is that it contains the ozone layer.  
• This layer absorbs ultraviolet radiation and shields life on Earth from intense, harmful forms of energy.  

Mesosphere

• The mesosphere lies above the stratosphere, which extends up to a height of 80 km.  
• In this layer, once again, temperature starts decreasing with the increase in altitude and reaches up to -100°C at the height of 80 km.  
• The upper limit of the mesosphere is known as the mesopause.  

Ionosphere

• The ionosphere is located between 80 and 400 km above the mesopause.  
• It contains electrically charged particles known as ions, and hence, it is known as the ionosphere.  
• Radio waves transmitted from the Earth are reflected back to the Earth by this layer.  
• Temperature here starts increasing with height.  

Exosphere

• The uppermost layer of the atmosphere above the thermosphere is known as the exosphere.  
• This is the highest layer but very little is known about it.  
• Whatever contents are there, they are extremely rarefied in this layer, and it gradually merges with outer space.  

We hope that class 11 Geography Book 1 Chapter 7 Composition and Structure of Atmosphere notes in English helped you. If you have any query about class 11 Geography Book 1 Chapter 7 Composition and Structure of Atmosphere notes in English or about any other notes of class 11 Geography Book 1 in English, so you can comment below. We will reach you as soon as possible…