Lecture Notes: Earth's Atmosphere

Objective

• Describe the structure and composition of Earth's atmosphere.
• Understand major gases and their relative abundances.
• Explain how temperature gradients define atmospheric layers.

Major Gases in Earth's Atmosphere

• Nitrogen (N2):
  • Makes up about 78% of the atmosphere.
  • Mostly non-reactive.
  • Requires fixation by bacteria or human activities to be usable by plants.
• Oxygen (O2):
  • Comprises about 21%.
  • Essential for respiration to break down glucose into ATP, the main energy source.
• Argon (Ar):
  • Accounts for about 0.93%.
  • Inert noble gas.
• Water Vapor (H2O):
  • Varies from 0% to 4% depending on conditions and region.
  • Considered a greenhouse gas but it cycles through the atmosphere quickly.
• Carbon Dioxide (CO2):
  • Makes up 0.04%.
  • Significant impact on atmospheric temperature due to its heat-trapping ability.
  • Affects ecosystems globally.

Layers of Earth's Atmosphere

Troposphere

• Closest to Earth's surface, up to 16 km.
• Where all weather occurs.
• Densest layer, holds most water vapor and gases.
• Ozone here is a pollutant, contributing to smog and respiratory issues.

Stratosphere

• Second layer, remember 'S' for second.
• Contains the ozone layer, blocking harmful UV radiation.

Mesosphere

• Middle layer, 'M' for middle.
• Gas molecules are less dense.
• Coldest temperatures found here at the mesopause.

Thermosphere

• Hottest layer.
• Absorbs highly damaging x-rays and UV rays.
• Contains aurora borealis (northern lights).

Exosphere

• Outermost layer, merges with outer space.

Temperature Changes in Atmosphere

• Troposphere: Temperature decreases with altitude.
• Stratosphere: Temperature increases due to UV absorption at the top.
• Mesosphere: Temperature decreases as gas molecules spread out.
• Thermosphere: Temperature increases sharply due to absorption of high-energy rays.

Science Skill

• Describe characteristics of an environmental concept visually.
• Identify layers with an inverse relationship between temperature and altitude.

Conclusion

• Temperature gradients characterize atmospheric layers.
• Practical activity: Visual identification of layers based on temperature changes.

Remember: Think like a mountain, write like a scholar.