Overview
This lecture explains the four major domains of Earth—lithosphere, hydrosphere, atmosphere, and biosphere—and their significance in making Earth habitable.
The Four Domains of Earth
- Earth’s habitability depends on four major domains: lithosphere, hydrosphere, atmosphere, and biosphere.
- The lithosphere, hydrosphere, and atmosphere combine to create the biosphere where life exists.
Lithosphere
- The lithosphere is the solid, outermost shell of the Earth, consisting of the crust and upper mantle.
- It is divided into continental crust (forms land masses) and oceanic crust (denser, found under oceans and seas).
Hydrosphere
- The hydrosphere includes all water on Earth, covering about 71% of the surface.
- Water exists as liquid (oceans, lakes), solid (ice), and gas (water vapor).
- Only 2.5% of Earth's water is consumable by humans.
Atmosphere
- The atmosphere is a protective layer of gases surrounding Earth, enabling weather, oxygen supply, and warmth.
- Main layers:
- Troposphere: lowest, weather occurs here, densest, extends 5-9 miles high.
- Stratosphere: up to 31 miles, contains the ozone layer reducing harmful UV rays.
- Mesosphere: burns up meteors.
- Thermosphere: absorbs solar radiation, location of auroras.
- Exosphere: outermost, merges with space.
Biosphere
- The biosphere consists of all regions where life exists, including land, water, and air.
- It is divided into the plant kingdom and animal kingdom.
- Oldest living organisms were bacteria, and the biosphere is nearly as old as Earth itself (~3.7 billion years).
Key Terms & Definitions
- Lithosphere — Earth’s solid outer layer, including the crust and upper mantle.
- Hydrosphere — All water present on Earth's surface.
- Atmosphere — The layer of gases enveloping the Earth.
- Biosphere — The global sum of all ecosystems, where life is found.
Action Items / Next Steps
- Remember to use water wisely and avoid wasting or contaminating it.