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The Earth's Atmosphere |
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| Composition
Layers
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| 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... |
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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. |
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Exosphere |  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 | 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. |
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| Mesosphere | 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. |
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| Stratosphere | 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. |
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| Troposphere | 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. |
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| 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. |
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