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What Are the Two Highest Layers of the Atmosphere?

Our atmosphere is comprised of a series of layers which differ in the amount of oxygen available and air density. The farther the distance of the atmosphere from Earth's surface does not correlate with getting colder. Instead, temperature fluctuates because of the concentration of varying molecules that either absorb or reflect the sun.

Exosphere
- The exosphere is the highest layer in the Earth's atmosphere. As the thinnest level of the atmosphere, the exosphere does not absorb sunlight because the molecules and atoms within escape into space. This is the level that first receives sunlight and the energy of the sun contained within.
Thermosphere
- The thermosphere is the upper-most part of the atmosphere that retains a high concentration of gas particles and molecules. These particles absorb ultraviolet and X-ray radiation and generate a surrounding temperature of more than 3,600 degrees Fahrenheit when they react with sunlight. This level of the atmosphere is essential to maintaining a normal temperature on Earth.
Secondary Layer Within Thermosphere
- The ionosphere is a secondary layer contained within the thermosphere. The ionosphere has electrically charged particles known as ions, which either contain a positive or negative charge. The chemical reaction of the molecules combined with radiation in the thermosphere creates the ionosphere.
Properties of the Ionosphere
- Radio frequencies are carried by the ionosphere.
  
  The ionosphere's ionic charges make it possible for radio signals to be heard worldwide because most radio wave frequencies bounce off of this layer and back to Earth. The aurora, or northern lights as they are often called, are a chemical reaction of ionized atoms that take place within the ionosphere.

Nature