Atmosphere
The layer of gases surrounding Earth held in place by gravity.
Definition
Earth's atmosphere is the layer of gas mixture—primarily nitrogen (78%), oxygen (21%), argon, and carbon dioxide—that surrounds the planet and is retained by Earth's gravity. It is divided into five main layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The atmosphere protects life by absorbing ultraviolet solar radiation, retaining heat through the greenhouse effect, and providing oxygen for respiration.
Example
“Astronauts returning from the International Space Station experience the protective role of Earth's atmosphere firsthand: their capsule heats to thousands of degrees as atmospheric friction slows it from 28,000 km/h, but the ablative heat shield protects them.”
Synonyms
- air envelope
- atmospheric layer
- gaseous envelope
Images
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Related Terms
- Greenhouse Effect
- Weather
- Climate
- Ozone Layer