The layer of the Earth's atmosphere where most planes fly is the TROPOSPHERE.
Closest to the surface of Earth, we have the troposphere. “Tropos” means change. This layer gets its name from the weather that is constantly changing and mixing up the gases in this part of our atmosphere.
The troposphere is between 5 and 9 miles (8 and 14 kilometers) thick depending on where you are on Earth. It’s thinnest at the North and South Pole.
This layer has the air we breathe and the clouds in the sky. The air is densest in this lowest layer. In fact, the troposphere contains three-quarters of the mass of the entire atmosphere. The air here is 78% nitrogen and 21% oxygen. The last 1% is made of argon, water vapor, and carbon dioxide.
When you feel the wind on your face, see clouds in the sky, and watch a bird flap its wings in flight, you’re experiencing the troposphere. It’s a pretty nice layer to call home.