An atmosphere is a blanket of gases enveloping a planet or other celestial body, held in place by gravity. Earth’s atmosphere sustains life, creates weather, and protects the planet from harmful solar radiation and meteoroids.
Composition
Earth’s atmosphere is a mixture of gases often referred to as air, composed primarily as below:
- Nitrogen (N₂): ~78%
- Oxygen (O₂): ~21%
- Argon (Ar): ~0.9%
- Trace Gases: Variable amounts of water vapor, carbon dioxide (CO₂), methane, and ozone.
Layers
The atmosphere is divided into five distinct layers, determined primarily by temperature changes with altitude:
- Troposphere: The lowest layer, where humans live, almost all weather occurs, and clouds form.
- Stratosphere: Contains the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the Sun.
- Mesosphere: The coldest layer, where most meteors burn up upon entering the atmosphere.
- Thermosphere: Contains the ionosphere; auroras occur here, and temperatures reach extremely high levels.
- Exosphere: The outermost layer, where the atmosphere gradually thins out and merges with the vacuum of outer space.
