Earth’s Life-Sustaining Atmosphere

The earth is the only planet which has life. The surface of the earth is a complex zone which has three main components of the environment viz. Lithosphere, Hydrosphere and Atmosphere. These 3 meet, overlap and interact and form a narrow zone called a Biosphere which sustains life. Along with land and water, air is a main part of this biosphere which plays a major role in regulating atmospheric activities. In this chapter, we will deal primarily with this composition of atmosphere and its major components. 

Atmosphere: A Journey Through the Layers and Composition of Atmosphere

• Composition of Atmosphere: The Composition of Atmosphere  is a gaseous layer surrounding the earth, which comprises a mixture of gases, water vapour, and dust particles. 
• Notably, 99% of the composition of the atmosphere’s total mass is concentrated within a range of 32 kilometres from the Earth’s surface. 

Composition of Atmosphere: Atmosphere’s Blueprint

 Composition of Atmosphere

• Composition of Gases: The Composition of Atmosphere consists mainly of Nitrogen(78%) and Oxygen(21%) and other gases . 
• • Nitrogen is essential for plant growth and Oxygen is indispensable for humans and animals for survival. 
  • At an altitude of 120 kilometers, oxygen becomes almost negligible.
• Carbon Dioxide and the Greenhouse Effect: Carbon dioxide, another critical gas, regulates Earth’s temperature and is transparent to incoming solar radiation but acts as a greenhouse gas, contributing to the greenhouse effect. 
  • In recent decades, carbon dioxide levels have been on the rise, mainly due to the burning of fossil fuels. 
• Protective Ozone Layer: Ozone, located between 10 and 50 kilometers (stratosphere) above the Earth’s surface, plays a crucial role in absorbing harmful ultraviolet rays from the sun. 
  • This ozone layer acts as a protective shield, safeguarding life on Earth.

• Particulate Matter: The Composition of Atmosphere also contains dust particles, including sea salts, fine soil, smoke-soot, ash, pollen, and dust from disintegrated meteors. 
  • Dust particles are more concentrated in subtropical and temperate regions due to dry winds. 

Atmospheric Layers: Earth’s Air in Five Distinct Zones

The Composition of Atmosphere is divided into distinct layers, each with its own characteristics .

1. Troposphere: Earth’s Dynamic Weather and Life Zone

• • It is the lowest layer with an average height of 13 kilometres.
  • It extends up to approximately 8 kilometres near the poles and about 18 kilometres at the equator. 
  • All weather changes and biological activities occur in this layer. 
  • In the Troposphere, temperature decreases at a rate of 1°C for every 165 metres of height.

2. Stratosphere: Guardian of Life with the Ozone Shield

• • It is located above the tropopause, and extends to a height of 50 kilometres. 
  • It contains the ozone layer, which absorbs harmful ultraviolet radiation from the sun, protecting life on Earth.

3. Mesosphere: Cold Depths and the Mesopause Boundary

• • It extends up to 80 kilometres, and is characterised by decreasing temperatures with altitude, reaching as low as minus 100°C at its upper boundary, known as the mesopause.

4. Ionosphere: Electric Heights and Radio Wave Reflection

• • This region spans from 80 to 400 kilometres above the mesopause. 
  • It contains electrically charged particles called ions and reflects radio waves back to Earth.

5. Exosphere: Earth’s Boundary with the Cosmos Beyond

• • It is the uppermost layer of the Composition of Atmosphere , where the atmosphere gradually merges with outer space. 
  • This layer contains extremely rarefied contents.

Key Concepts Related to Composition of Atmosphere

Weather Instruments

Weather and Climate: Daily Changes and Long-Term Patterns

• Definition: Weather is the day-to-day condition of the atmosphere, affecting our daily lives and activities.
• Components:  It can change dramatically and includes factors like temperature, air pressure, wind, and humidity.
• Climate, on the other hand, represents the long-term average weather patterns of a place.
  • Studies related to weather and climate help us plan and adapt to changing conditions.

Temperature: Diurnal, Seasonal, and Urban Impacts

• Temperature indicates the degree of hotness or coldness in the air.
• Diurnal and Seasonal Variation:  It varies between day and night and from season to season, with summers being hotter than winters.
• Insolation: The incoming solar energy affects temperature distribution, decreasing from the equator to the poles.
• Urban Heat Islands:  Urban areas, compared to villages, have higher temperatures due to buildings and roads absorbing heat.