Earth's atmosphere is a complex, layered system primarily composed of nitrogen and oxygen, essential for supporting life on our planet.
Here's a breakdown of its key characteristics:
1. Composition:
- Approximately 78% nitrogen (N₂)
- Approximately 21% oxygen (O₂)
- Approximately 1% other gases, including argon, carbon dioxide, neon, helium, methane, krypton, hydrogen, nitrous oxide, ozone, CFCs (chlorofluorocarbons), and water vapor. The proportion of water vapor varies.
2. Structure (Layers): The atmosphere is divided into five main layers, based on temperature gradients:
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Troposphere: This is the lowest layer, extending from the Earth's surface up to about 7-20 km (4-12 miles). It contains the majority of the atmosphere's mass and is where weather occurs. Temperature decreases with altitude.
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Stratosphere: Located above the troposphere, extending to about 50 km (31 miles). Contains the ozone layer, which absorbs harmful UV radiation from the sun. Temperature increases with altitude due to ozone absorption.
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Mesosphere: Above the stratosphere, extending to about 85 km (53 miles). Temperature decreases with altitude, making it the coldest layer. Meteors burn up in this layer.
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Thermosphere: Extends from about 85 km (53 miles) to 500-1,000 km (311-621 miles). Temperature increases with altitude due to absorption of energetic solar radiation. The International Space Station orbits in this layer.
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Exosphere: The outermost layer, gradually fading into space. Extends from the top of the thermosphere outwards. There is no clear upper boundary.
3. Pressure:
- Atmospheric pressure decreases with altitude. At sea level, the standard atmospheric pressure is about 1013.25 millibars (mb) or 29.92 inches of mercury (inHg).
4. Temperature:
- Temperature varies significantly with altitude and atmospheric layer, as described above. This variation is influenced by factors such as solar radiation absorption and the presence of certain gases (e.g., ozone).
5. Density:
- Air density also decreases with altitude. The density of the air is greatest near the Earth's surface and decreases exponentially with height.
6. Importance:
- Provides breathable air for life.
- Protects from harmful solar radiation (UV).
- Moderates Earth's temperature through the greenhouse effect.
- Facilitates the water cycle.
- Burns up meteors before they reach the surface.
In summary, Earth's atmosphere is a dynamically layered system characterized by its unique composition, pressure, temperature, and density profiles, all crucial for supporting life and maintaining the planet's climate.
