A1-2 The Atmosphere
The layers of the Earth's atmosphere.

The atmosphere is the subsystem that is best described as the gas envelope that surrounds our planet. It consists primarily of nitrogen (78%) and oxygen (21%), and extends to an altitude of approximately 100 kilometers (approximately 62 miles).

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The main components of the Earth’s atmosphere

The atmosphere is composed of the following gases:

Gas Percentage Composition
   
Nitrogen 78%
Oxygen 21%
Other (Argon, Carbon Dioxide, Helium, etc.) 1%
  1. Prepare a properly labeled pie graph illustrating the main components of the atmosphere.

    Composition of the Earth's atmosphere.
  2. Approximately what fraction of the atmosphere is composed of oxygen?

    21% = 21/100 ≈ 1/5

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An astronaut peering out of the windows of the International Space Station can see the real relative thickness of the Earth's atmosphere.

The Thin Atmosphere

The view to the right in the main view panel clearly shows the atmosphere as a relatively thick layer. This is because you are looking at a zoomed-in view of the Earth. The Earth, however, has an average diameter of 12,742 km (7,917.5 miles). In reality, the 100 km (62 miles) thick atmosphere provides a very, very thin skin around our massive globe.


  • Zoom out in the globe view to the right until the entire Earth is visible. This gives a more representative view of the relative thickness of the atmosphere when compared to the whole Earth.