Eye to the sky
How the Earth’s atmosphere stacks up
Although the Earth’s atmosphere extends 10,000km above the planet’s surface, the mix and density of the gases change as the distance from the Earth increases. The temperature also changes with altitude, and scientists use these changes to classify the atmosphere into five main layers. From the lowest to the highest, these layers are:
Troposphere
This layer begins at the surface of the Earth and extends out to between 9km at the poles and 17km at the equator. The lowest layer of the troposphere consists of the planetary boundary layer (PBL), which extends from the Earth’s surface to a height that ranges anywhere from 100 to 3,000m. The PBL contains much of the pollutants emitted from the ground.
The troposphere contains approximately 80 percent of the atmosphere’s mass and is known as the lower atmosphere.
Stratosphere
The layer above the troposphere,
this layer extends to about 51km above the Earth’s surface. The temperature increases with height due to increased absorption of ultraviolet radiation by the ozone layer.
Mesosphere
The mesosphere reaches about 80 to 85km above the surface of the Earth. The temperature decreases with height, and the top of the mesosphere is the coldest place on Earth, with an average temperature of about -85°C (-120°F). The stratosphere and mesosphere constitute the middle atmosphere.
Thermosphere
The top of the thermosphere extends up to about 350 to 800km above the Earth’s surface. This layer is known as the upper atmosphere.
Exosphere
This layer extends from the top of the thermosphere to thousands of kilometers above the surface of the Earth. It has very few atmospheric molecules in it, and these molecules can escape into space.
