Page 34 - Beginner's Guide to Aviation

1. Exosphere
Upper boundary: 10,000 km
Lower boundary: 500 - 1000 km
The Exosphere is the uppermost atmospheric layer, the last layer right before space! It contains some of the lightest gases such as hydrogen, helium, carbon dioxide and atomic oxygen.
2. Thermosphere
Upper boundary: 640 km
Lower boundary: 80 – 85 km
This layer is where the International Space Station orbits and where beautiful auroras occur. However, within this layer ultraviolet radiation causes ionisation which is harmful to us.
These two layers make up the Ionosphere because they are ionised by solar radiation. This solar radiation generates different layers of ionisation and influences radio propagation.
3. Mesosphere
Upper boundary: 80 – 85 km
Lower boundary: 50 km
The Mesosphere is the middle layer amongst all the layers. It is where the highest clouds can be found and where most meteors start to burn up when they enter the Earth’s atmosphere.
The next 2 layers, the Stratosphere and Troposphere have different values for its lower and upper boundaries respectively due to the different in temperatures at the Earth’s poles and equator. The Earth’s poles receive lesser solar energy as compared to the equator due to the Earth’s curvature. Therefore, the temperatures at the Earth’s poles are much cooler than the temperature at the equator. As air expands in higher temperatures and contracts in lower temperature, the boundaries at the poles are lower than the boundaries at the equator. These 2 layers are also the only atmospheric layers where commercial airliners cruise!