Layers of Atmosphere 

• The atmosphere is made up of five distinct layers that are determined by the changes in temperature that happen with increasing altitude.

• On the basis of layer atmosphere is divided into five types, they are: 

      1) Troposphere 
      2) Stratosphere 
      3) Mesosphere 
      4) Thermosphere 
      5) Exosphere 

Troposphere: 

• It is the lowest most layer present in the atmosphere and extends upward to approx 10kms above sea level starting from ground level. 

• Boundary of the layer is the lowest part of the troposphere and tropopause is the outermost part of the troposphere. 

• 75% of the air which is present in the atmosphere is there in the troposphere.

•  As 99% of the atmospheric water vapour is present in this layer only, so most of the cloud appears in this layer. 

• As you move up in the troposphere , the temperature and air pressure drop down.  (temperature decreases with increasing altitude)

• When a parcel of air moves upwards it expands. When air expands it cools and because of this reason only the base of the troposphere is warmer. 

• Its base is warmer because the air in the surface of the Earth absorbs the sun’s energy, gets heated up and moves upward as a result of which it cools down. 

Stratosphere: 

• The layer above the troposphere is the stratosphere. 

• This layer extends from the top of the troposphere to about 50 km (31 miles) above the ground. 

• In the stratosphere only the ozone layer is present as the ozone molecules in the layer absorb high-energy ultraviolet (UV) light from the Sun and convert it into heat. 

• And because of this reason as you move up your temperature increases. (temperature increases with increasing altitude)

Mesosphere: 

• Mesophere is present just above the stratosphere layer and it extends to a height of about 85 km (53 miles) from the ground. 

• In this layer temperature becomes colder as you move up through this layer.  (temperature decreases with increasing altitude)

• This layer is the coldest part of the atmosphere as temperature reaches -90 C in this layer. 

Thermosphere: 

• The layer which is present above the mesosphere is the thermosphere. 

• In this region temperature increases as we move up or go higher. (temperature increases with increasing altitude)

• This increase in temperature in this region is because of the absorption of energetic ultraviolet and X-Ray radiation from the sun. 

• The air in this layer is very thin as because of this there is freezing cold in this layer. 

• Different satellites orbit the Earth within this layer only. 

• The temperature is about 500° C to 2,000° C or higher in the upper thermosphere. 

• The aurora, the Northern Lights and Southern Lights, occur in the thermosphere. 

Exosphere: 

• This layer is the final frontier of the Earth’s gaseous envelope. 

• Air which is present in the exosphere slowly slowly leaking out of the Earth’s atmosphere into outer space. 

• As there is no exact boundary between where the exosphere finally fades away into space. 

Ionosphere: 

• This layer is not any distinct layer unlike other layers present in the atmosphere. 
• It is a series of regions in parts of the mesosphere and thermosphere where high-energy radiation from the Sun has hitted electrons loose from their parent atoms and molecules

Composition of Atmosphere 

• As the atmosphere is a mixture of different gases along with that it also contains huge numbers of solid and liquid particles, collectively called ‘aerosols’. 

• There are few gases which are known as permanent atmospheric components which remain in fixed proportion to the total gas volume whereas other quantities of substance vary in proportion from time to time. 

• If we exclude suspended particles, water vapour and various other gases from the atmosphere then in that case the dry air is very stable all over the earth up to an altitude of about 80 kilometres. 

• In the higher layer of the atmosphere the proportion of gases changes in such a way that oxygen will be almost in negligible quantity at the height of 120 km. In the same way carbon dioxide and water vapour are present only up to 90 km from the surface of the earth. 

• 99% of clean and dry air is made up of Nitrogen and Oxygen and remaining gases like inert and constitute, contribute only about 1% of the atmosphere. 

• Besides these gases, large quantities of water vapour and dust particles are also present in the atmosphere. These solid and liquid particles are of great climatic significance. 
• Different constituents of the atmosphere, with their individual characteristics, are discussed below. 

• Along with gases large quantities of water vapour and dust particles are also present in the atmosphere. Further these solid and liquid particles show great significance on the climate

Gases Present in the Atmosphere: 

A. Oxygen: 

• 21% of total atmospheric volume is constituted by oxygen and also known as the most important gas of the atmosphere. 

• As all living organisms are dependent on oxygen for the inhaling process along with that it also combines with other elements to form important compounds, such as oxides. Also, combustion is not possible without oxygen.

B. Nitrogen: 

• It constitutes 78% of atmospheric volume and is relative to inert gases. 

• It is considered as important contitutens of all organic compounds. The major function of nitrogen Nitrogen accounts for 78% of total atmospheric volume. 

• It is a relatively inert gas, and is an important constituent of all organic compounds. 

• The main function of nitrogen is to control combustion by diluting oxygen and also helps in indirect oxidation

Structure of Atmosphere NCERT Notes FAQs 

Q1. Explain the term greenhouse effect? 

Ans. 

• When the gases present in the atmosphere traps the Sun’s heat then this process is known as the greenhouse effect. 

• Because of this process the temperature of Earth's surface increased more than initially which was because of the atmosphere. 

• Because of the greenhouse effect, Earth is a comfortable place to live. 

Q2. What is ozone? 

Ans. 

• It is important gas which is present in the atmosphere and it is type of oxygen molecule as ozone is made up of three oxygen molecules i.e. It is less than 0.00005% percent of the total volume of the atmosphere. 

• Its major function is that it blocks the harmful ultraviolet radiation from the sun. 

Q3. How important is the atmosphere? 

Ans. The atmosphere is an important part of what makes Earth livable. It blocks some of the Sun's dangerous rays from reaching Earth. It traps heat, making Earth a comfortable temperature. And the oxygen within our atmosphere is essential for life. 

Q4. What are the 5 types of atmosphere? 

Ans. Earth's atmosphere has five major and several secondary layers. From lowest to highest, the major layers are the troposphere, stratosphere, mesosphere, thermosphere and exosphere 

Q5. What are the components of the atmosphere? 

Ans. Atmosphere has 3 major components i.e Nitrogen, Oxygen and Carbon dioxide. There are other minor components such as methane, neon, helium, hydrogen, krypton and water vapor.

Key Takeaways for UPSC Aspirants

• Major Components: The Earth's atmosphere is composed of approximately 78% Nitrogen (N₂), 21% Oxygen (O₂), and around 1% Argon (Ar). These gases are the primary constituents by volume.
• Trace Gases: Besides the major components, the atmosphere contains trace gases such as Carbon Dioxide (CO₂) at about 0.04%, Neon (Ne), Helium (He), Methane (CH₄), Krypton (Kr), and Hydrogen (H₂). These trace gases play crucial roles in atmospheric processes.
• Variable Gases: Water vapor (H₂O) is a significant variable component, ranging from about 0.2% to 4% depending on location and conditions. It is essential for the hydrological cycle and weather patterns.
• Ozone Layer: Ozone (O₃) exists in small amounts in the atmosphere, with its concentration peaking in the stratosphere. The ozone layer is vital for protecting life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun.
• Aerosols and Particulates: The atmosphere contains aerosols and particulate matter, including dust, pollen, soot, and sea salts. These particles can influence climate and weather, and impact air quality and human health.
• Greenhouse Gases: Important greenhouse gases include Carbon Dioxide (CO₂), Methane (CH₄), Nitrous Oxide (N₂O), and water vapor. These gases trap heat in the atmosphere, contributing to global warming and climate change.
• Stratification of the Atmosphere: The atmosphere is divided into distinct layers based on temperature gradients: the Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Each layer has unique characteristics and functions.
• Human Impact: Human activities, such as burning fossil fuels, deforestation, and industrial processes, have altered the atmospheric composition by increasing concentrations of greenhouse gases and pollutants, leading to environmental issues like global warming, acid rain, and ozone depletion.