Earth's Atmosphere and Composition

Earth's Atmosphere

• Earth's atmosphere is a dynamic system.
  • It has inputs, outputs, flows and storages.
• Solar radiation is the main energy input to the atmosphere.
• The atmosphere is a thin blanket of gases and particles (air).
• The atmosphere is vital for life on Earth:
  • It regulates temperature.
  • It provides oxygen for respiration.
  • It protects us from harmful UV radiation.
• The atmosphere, along with water, creates a unique environment for life on Earth.
• The atmosphere influences and is influenced by life, creating a biogeochemical system.

Atmospheric Composition

• Photosynthesis is the primary source of oxygen in the atmosphere.
  • Plants use carbon dioxide (CO2) and water (H2O) to create sugars and oxygen (O2) in the presence of sunlight.
  • The chemical reaction for photosynthesis is: 6CO2 + 6H2O + solar energy → C6H12O6 (sugar) + 6O2
• Respiration uses oxygen to convert sugar into energy.
  • Both plants and animals use oxygen for respiration.
  • The chemical reaction for respiration is: C6H12O6 + 6O2 → 6CO2 + 6H2O + usable energy.
• Greenhouse gases trap heat in the atmosphere.
  • Examples include carbon dioxide, methane, water vapor, and ozone.
• Ozone (O3) in the upper atmosphere filters harmful ultraviolet (UV) radiation from the sun, making life on Earth's surface possible.

Atmospheric Layers

Troposphere

• Lowest layer of the atmosphere, in direct contact with Earth's surface.
• Temperature decreases with altitude, about 6.5°C per kilometer.
• Weather occurs in the troposphere.
• Greenhouse gases regulate temperature in this layer.

Stratosphere

• Layer above the troposphere.
• Temperature is mostly constant, around -60°C in the lower stratosphere.
• Winds increase with height.
• Contains the ozone layer, located in the upper stratosphere.
• Contains little water vapor due to the cold temperatures.

Mesosphere

• Third highest layer of the atmosphere.
• Temperature decreases with altitude.
• Coldest part of the atmosphere.
• Strong zonal winds (east-west), atmospheric tides, planetary waves, and gravity waves are found here.

Thermosphere

• The region between 100 km and 500 km above Earth's surface.
• Temperature increases sharply in the lower thermosphere and then levels off with altitude.
• UV and X radiation from the sun is absorbed, causing molecules to break apart into atoms.
• Temperature continues to increase with altitude.

Atmospheric Circulation

• The strength of atmospheric circulation is controlled by a dynamic balance between processes that emit oxygen (photosynthesis) and consume oxygen (respiration).
• The atmosphere plays a role in the hydrologic cycle, holding a significant amount of water as water vapor.
• Sound waves travel through the atmosphere.