The Atmosphere

• The atmosphere consists of a layer of gases, collectively referred to as air, that surrounds Earth.

• Air is composed mostly of nitrogen (78%) and oxygen (21%), with small amounts of other gases, including argon (0.9%) and carbon dioxide (0.04%).

• The atmosphere also contains, on average, about 0.4% water vapour.

The atmosphere is a layer of air that surrounds Earth.
It consists mostly of nitrogen and oxygen.

(Image: NASA)

• The atmosphere is divided into five main layers which are defined by their temperature profiles. In order of increasing distance from Earth’s surface, these layers are:

• The troposphere – the layer containing the air we breathe and where most weather events are generated.

• The stratosphere – the layer containing the ozone layer, which absorbs harmful ultraviolet radiation and protects life on Earth.

• The mesosphere – the layer where most meteors burn up.

• The thermosphere – the layer where the auroras occur and where most satellites orbit Earth.

• The exosphere – the transition region between the atmosphere and outer space.

• Temperature alternately decreases and increases between different layers of the atmosphere.

• This limits the movement of air between layers.

• Air pressure (atmospheric pressure) and air density both decrease exponentially with altitude.

• Consequently, about 75% of all air and almost all water vapour exists in the lower atmosphere (troposphere).

The atmosphere consists of five main layers.

(Image: anuwat, Adobe Stock)