title banner
weather features homepagewhat is weather?weather forecastingwhat powers the weather?precipitation sectionwind sectionthe changing climate

 

The Earth's Atmosphere

Composition                         Layers

 

Atmosphere... The Earth is surrounded by a blanket of air called the atmosphere. The atmosphere is made up of various gases that act as a protective shield for the Earth and allow life to exist. Without it, we would be burned by the intense heat of the sun during the day or frozen by the very low temperatures at night.
Composition...

Atmospheric composition

More than three quarters of the atmosphere is made up of nitrogen and most of the rest is oxygen.  However it is the remaining 1%, a mixture of carbon dioxide, water vapour and ozone, that not only produces important weather features such as cloud and rain, but also has considerable influence on the overall climate of the Earth,through mechanisms such as the greenhouse effect and global warming.  (Stay with us and we'll learn more about the changing climate in a later section!)
Pressure... The atmosphere consists of five layers, held around the planet by the force of gravity. As you move upwards through the layers, atmospheric pressure decreases rapidly with height and the air temperature also changes. It is these, more complicated, changes in temperature which are used to divide the atmosphere into the layers described below.top of page

Atmospheric layers

Exosphere REDBALL1.GIF (137 bytes)   Above a height of about 500km is the exosphere, a layer where the atmosphere merges into space. Satellites are stationed in this area, 500km to 1000km from Earth.
Thermosphere REDBALL1.GIF (137 bytes)   The thermosphere is the fourth layer in the atmosphere, between 80km and 110km above the Earth. Space shuttles fly in this area and it is also where the aurora lights are found. Auroras are wispy curtains of light caused when the sun strikes gases in the atmosphere above the Poles.
Mesosphere REDBALL1.GIF (137 bytes)   Beyond the stratosphere the air is very thin and cold. This area is known as the mesosphere, and is found between 50km and 80km above the Earth’s surface.
Stratosphere REDBALL1.GIF (137 bytes)   The stratosphere is the second layer of air above the Earth’s surface and extends to a height of 50km. It is here that we find the ozone layer. The ozone layer absorbs much of the sun’s harmful radiation that would otherwise be dangerous to plant and animal life.
Troposphere REDBALL1.GIF (137 bytes)  The troposphere is the layer closest to the Earth, approximately 11km high. Weather occurs only in the troposphere because it is this layer that contains most of the water vapour. Weather is the way water changes in the air, and so without water there would be no clouds, rain, snow or other weather features.
The troposphere is an unstable layer where the air is constantly moving. As a result, aircraft flying through the troposphere may have a very bumpy ride – what we know as turbulence. You may have experienced this when flying before! Because of this turbulence, most jet airlines fly higher above the Earth in the stratosphere. Here the air is more still and clear as they can fly above the clouds.
 

Although the atmosphere extends to a height of 1000km, it is nevertheless still very important for life on the surface of the Earth.  This is because of something known as air pressure, which we will learn more about on the next page. 

top of page

previous next