Notes

Troposphere
Living at the surface of the Earth, we are usually only aware of the events happening in the lowest layer, the troposphere, where all weather occurs. The base of this layer is warmer than its top because the air is heated by the surface of the Earth, which absorbs the Sun’s energy.

Stratosphere
Above the troposphere lies the stratosphere where jet airplanes fly. Temperatures increase with altitude because of increasing amounts of ozone. The ozone layer within the stratosphere absorbs harmful ultraviolet rays of sunlight.

Mesosphere
As the mesosphere extends upward above the stratosphere, temperatures decrease. The coldest parts of our atmosphere are located in this layer and can reach –90°C.

Thermosphere
In the forth layer from Earth’s surface, the thermosphere, the air is thin, meaning that there are far fewer air molecules. The thermosphere is very sensitive to solar activity and can heat up to 1,500°C or higher when the Sun is active making an aurora that lights up the night sky. Astronauts orbiting Earth in the space station or space shuttle spend their time in this layer.

Exosphere
The upper layer of our atmosphere, where atoms and molecules escape into space, is called the exosphere.