Introduction to Earth's Atmosphere

Structure of the Atmosphere

• The atmosphere is a thin shell of gases between the Earth and outer space.
• Comparable to the skin of an apple (atmosphere) to the fruit (solid Earth).

Composition of the Atmosphere

• Permanent Gases (majority of atmosphere):
  • Nitrogen (N2): 78%
  • Oxygen (O2): 21%
  • Argon: 0.93%
  • Minor components include Neon, Helium, Hydrogen, and Xenon.
• Variable Gases (Trace Gases) (less than 1% of the atmosphere):
  • Water Vapor
  • Carbon Dioxide
  • Methane
  • Nitrous Oxide
  • Ozone
  • Particulates (solids suspended in air)
  • Chlorofluorocarbons (CFCs)
• Though in small quantities, trace gases significantly impact climate (e.g., Carbon Dioxide as a greenhouse gas).

Atmospheric Pressure

• 90% of atmospheric mass is in the lowest 10 km due to gravity.
• Air pressure decreases with altitude because fewer air molecules exert force.
  • Higher altitude = lower air pressure (e.g., mountain tops).
  • Lower altitude = higher air pressure (e.g., valleys).
• Air pressure measured in millibars.

Temperature Variations with Altitude

• Temperature changes in a complex manner with altitude, featuring multiple peaks and valleys.
• Atmospheric Layers:
  • Troposphere: Lowest layer; temperature decreases with altitude; contains greenhouse gases and weather occurrences.
  • Stratosphere: Above troposphere; temperature increases with altitude; contains the ozone layer.
  • Mesosphere: Low air density; temperature decreases with altitude.
  • Thermosphere: Extremely low air density; strong solar radiation; temperature increases with altitude.

Boundaries Between Layers

• Boundaries are labeled with "-pause" suffix:
  • Tropopause: Between Troposphere and Stratosphere.
  • Stratopause: Between Stratosphere and Mesosphere.
  • Mesopause: Between Mesosphere and Thermosphere.

Key Characteristics of Atmospheric Layers

Troposphere: Weather occurs here, and temperature decreases with height. This is where we find greenhouse gases in the atmosphere and where we live.

• Stratosphere: Above Troposphere, Contains ozone layer; temperature increases with height.
• Mesosphere: Very low air density; temperature decreases with height.
• Thermosphere: Very close to outer space; very low air density and strong solar radiation.

Review Questions

1. What are the three most prevalent gases in the atmosphere?
   • Nitrogen, Oxygen, Argon
2. Does temperature increase or decrease with height in the troposphere?
   • Temperature decreases
3. Does pressure increase or decrease with height in the troposphere?
   • Pressure decreases