Earth Science: Atmosphere and Subsystems

Earth’s Subsystems

• Earth consists of four main subsystems: atmosphere, hydrosphere, geosphere, and biosphere.
• Biogeochemical cycles refer to the flow of chemical elements between biological and geological systems.

Atmosphere: The Earth’s Blanket

• The atmosphere is a protective layer of gases surrounding Earth, held by gravity.
• It shields life from harmful ultraviolet radiation, enabling biological processes.

Composition of the Atmosphere

• Nitrogen makes up 78.084% of the atmosphere.
• Oxygen constitutes 20.946%, while argon is present at 0.934%.
• Trace gases include carbon dioxide (0.036%), neon (0.00182%), and methane (0.00015%).

Layers of the Atmosphere

• Troposphere:

  • Extends from the surface to 8-15 kilometers (5-9 miles).
  • Temperature decreases with altitude; weather phenomena mainly occur here.

• Tropopause:

  • Boundary layer between the troposphere and stratosphere.
  • Commercial aircraft typically fly in this region.

• Stratosphere:

  • Ranges from 15 to 50 kilometers (9-31 miles).
  • Contains the ozone layer; temperature increases with altitude.

• Mesosphere:

  • Spans from 50 to 85 kilometers (31-53 miles).
  • Temperature decreases with altitude; it protects against meteorites.

• Thermosphere:

  • Reaches up to 600 kilometers (373 miles).
  • Temperature rises with altitude, absorbing high-energy radiation like X-rays.

• Ionosphere:

  • Overlaps with the thermosphere, marked by charged particles.
  • Regions display auroras due to ion interactions.

• Exosphere:

  • The outermost layer, extending to 3,000 kilometers (1,864 miles).
  • Composed mainly of hydrogen and helium; experiences extreme high temperatures (up to 987°C).

Hydrosphere: The Earth’s Water

• The hydrosphere encompasses all of Earth’s water, including frozen portions termed the cryosphere.
• Water exists as oceans, seas, lakes, and surface bodies.

Distribution of the Hydrosphere

• Saltwater makes up 97% of the total hydrosphere, with an average salinity of 35%.
• Freshwater constitutes 3% of the hydrosphere; it includes:
  • Groundwater: 30.1%
  • Ice Sheets & Glaciers: 68.7%
  • Other surface water: 0.3%

Cryosphere

• The cryosphere encompasses all frozen water on Earth, including snow, ice, and glaciers.
• The term derives from the Greek word 'kryos', meaning cold.