The environment has four major components: the air, the land, the water and the living organisms which inhabit it. Scientists have given special names for each by creating words based on Greek vocabulary. The first component of the environment is called the atmosphere. The atmosphere contains gases such as nitrogen, oxygen and a small amount of carbon dioxide. The next category of the environment is where all the water is found. It is called the hydrosphere. Bodies of water such as lakes, streams and the oceans form the hydrosphere. The lithosphere is the rock crust of the Earth. The entire planet is covered by the lithosphere, even though most of it has a layer of water on top called the oceans. The last category of the environment is what makes the Earth unique: the biosphere. The biosphere is where all life is found.

The Atmosphere
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Although it is almost entirely invisible, the atmosphere is the easiest part of the Earth's environment to study. Most of the hydrosphere and the lithosphere are difficult to access and remain largely unexplored. The atmosphere, however, has very few mysteries. Just about every cubic metre of it has been observed by scientists or satellites.

Composition of the Air

Over 200 years ago, the French scientist Antoine Lavoisier measured the chemical composition of air. Since the gases which make up the atmosphere are invisible, the best way to visualize them is by expressing them as percentages and by using a pie chart. It is important to note that oxygen gas, whose chemical symbol is 0₂, is not the main component of air and that carbon dioxide, C0₂, represents much less than one percent.

Ultraviolet Radiation and Heat

Even though it is invisible, the atmosphere is very important for life on this planet. First of all, the atmosphere protects the surface from too much ultraviolet radiation. Ultraviolet radiation, or UV radiation, is a type of energy from the sun which, in high doses, can be dangerous for living organisms. UV radiation is responsible for giving people sun burns. Too much of it causes skin cancer.

The atmosphere protects the Earth's surface in two ways. The first way is that gases in the atmosphere are capable of absorbing certain types of radiation, like a sponge absorbs water. The second way is by reflecting radiation in the same way that a mirror reflects light. As a result, very little UV radiation from the Sun ever gets to the Earth's surface.

Heat, another type of energy, is absorbed or reflected by the gases in the atmosphere. Some of the heat from the Sun is reflected by the atmosphere so that the Earth does not get too hot. At night, the atmosphere prevents the Earth's heat from escaping into space. As a result, the surface does not get too cold at night.

Problems and Concerns caused by Human Influences on the Environment : Acid Rain (Opens in new window.)

The Greenhouse effect
Is there life on Mars?

• The Earth
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• Weather and Climate
• Hydrosphere, Lithosphere and Biosphere
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© Paul Billiet, Shirley Burchill, Alan Damon and Deborah James 2008