The atmosphere

Earth's atmosphere contains 77 per cent nitrogen, 21 per cent oxygen, with traces of argon, carbon dioxide and water.

In recent years the amount of carbon dioxide in the atmosphere has been increasing, due mainly to the burning of fossil fuels. At the same time people are cutting down forest trees that use carbon dioxide. The increase in carbon dioxide levels has resulted in higher average temperatures via the greenhouse effect. Carbon dioxide gas allows sunlight to reach the surface of Earth but prevents heat from escaping, and in this way the atmosphere warms up. However, without the greenhouse effect surface temperatures would be much lower than they currently are.

Oxygen began to accumulate in the atmosphere when primitive life-forms (the first bacteria and plants) began to photosynthesise. Increases in oxygen levels allowed more forms of life to evolve.

The atmosphere of Earth has a number of layers (see Figure 6.8). Each layer corresponds to changes in pressure and temperature.

0 0

Post a comment