Geography Lesson 8

Composition and Structure of the Atmosphere

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1. Introduction

The Earth is surrounded by a thick blanket of air called the atmosphere. It extends up to about 10,000 km above the Earth’s surface. Though it appears invisible, it plays a very important role in supporting life on Earth.

The atmosphere:

• Provides oxygen for breathing.
• Protects living beings from harmful solar radiation.
• Maintains the Earth’s temperature.
• Helps in weather formation and the water cycle.

Without the atmosphere, the Earth would be extremely hot during the day and extremely cold at night, and life would not be possible.

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2. Composition of the Atmosphere

The atmosphere is a mixture of different gases, water vapour, and dust particles. This mixture is called air.

A) Major Gases (Permanent Components)

These gases remain almost constant in proportion.

Gas	Percentage	Importance
Nitrogen	78%	Helps in plant growth and reduces burning rate of oxygen
Oxygen	21%	Essential for respiration and combustion
Argon	0.93%	Inert gas, does not react easily
Carbon Dioxide	0.03%	Used in photosynthesis

1. Nitrogen (78%)

• The largest component of the atmosphere.
• It controls the rate of burning.
• Plants absorb nitrogen from the soil (nitrogen cycle).

2. Oxygen (21%)

• Necessary for breathing.
• Supports combustion.
• Essential for survival of animals and humans.

3. Carbon Dioxide (0.03%)

• Absorbed by plants during photosynthesis.
• Helps in maintaining Earth’s temperature (greenhouse effect).
• Increased CO causes global warming.

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B) Variable Components

These components change according to time and place.

1. Water Vapour

• Amount varies from 0% to 4%.
• Responsible for cloud formation and rainfall.
• Regulates temperature.
• Plays important role in weather conditions.

2. Dust Particles

• Include smoke, pollen, salt particles, etc.
• Help in condensation process.
• Necessary for cloud formation.
• Excess dust causes air pollution.

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3. Structure of the Atmosphere

The atmosphere is divided into five layers based on temperature changes.

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1? Troposphere

• Lowest layer of the atmosphere.
• Extends up to 8 km at poles and 18 km at equator.
• Contains 75% of the total atmospheric mass.
• All weather phenomena occur here (rain, clouds, storms, winds).
• Temperature decreases with height (about 6.5C per 1000 meters).
• Contains most of the water vapour and dust particles.

This is the most important layer for life.

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2? Stratosphere

• Lies above the troposphere.
• Extends up to 50 km.
• Contains the Ozone Layer.
• Temperature increases with height due to absorption of ultraviolet rays.
• Weather is calm and stable.
• Jet aeroplanes fly in this layer.

Ozone Layer

• Protects Earth from harmful ultraviolet (UV) rays.
• Ozone depletion leads to skin cancer and environmental problems.

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3? Mesosphere

• Extends from 50 km to 80 km.
• Temperature decreases with height.
• Coldest layer of the atmosphere.
• Meteors burn up in this layer due to friction.

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4? Thermosphere

• Extends from 80 km to 400 km.
• Temperature increases rapidly.
• Very thin air.
• Ionosphere is a part of this layer.
• Radio waves are reflected here.
• Northern and Southern Lights (Aurora) occur here.
• Artificial satellites orbit in this region.

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5? Exosphere

• Outermost layer.
• Extends beyond 400 km.
• Very thin air.
• Gradually merges into outer space.
• Hydrogen and helium gases are found here.

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4. Importance of the Atmosphere

The atmosphere plays a vital role in maintaining life on Earth:

1. Protection from Harmful Radiation

• Ozone layer absorbs ultraviolet rays.

2. Maintains Temperature

• Acts like a blanket.
• Prevents extreme temperature differences.

3. Supports Life

• Provides oxygen and carbon dioxide.

4. Weather Formation

• Winds, rainfall, storms occur in the atmosphere.

5. Water Cycle

• Evaporation, condensation and precipitation happen due to atmospheric processes.

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5. Environmental Concerns

Human activities are affecting the atmosphere:

• Air pollution
• Global warming
• Ozone depletion
• Greenhouse effect

We must:

• Reduce pollution.
• Use renewable energy.
• Plant more trees.
• Control industrial emissions.

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6. Conclusion

The atmosphere is an essential and life-supporting layer around the Earth. Its composition and structure help maintain temperature, protect living organisms, and regulate weather systems. Protecting the atmosphere is necessary for the survival of present and future generations.

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