Earth Science: Atmosphere and Subsystems

Study Notes

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.

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

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%).

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).

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

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%