Chapter 8 of 10All chapters
Chapter 8 of 10
The atmosphere
A thin shell of gas.
Composition and layers
Roughly 78 percent nitrogen and 21 percent oxygen, with trace gases doing most of the interesting work. It thins with height through the troposphere, stratosphere and beyond.
- Almost all weather happens in the lowest layer.
- The ozone layer in the stratosphere absorbs most ultraviolet radiation.
Why it stays
Gravity holds it and the magnetic field shields it from the solar wind. Mars lost most of its atmosphere partly for lack of that protection.