A british scientist, James Lovelock, proposed the idea of the world being one organsim that maintains the conditions needed for it to survive. This theory is called the Gaia Hypothesis comming from the Greek words "Mother Earth"

Lovelock was assigned by NASA to determine the chances of life existing on other planets other than the earth. He thought that the only way of doing this was to send a vehicle to land on these planets to gather samples of soil and test it for signs of life. As Lovelock thought more about this, he felt that it was not neccesary to do this. He felt that if he examined the composition of the planet and the surface temperature of the planet, he would be able to tell if there was chance that life would be able to exist on that planet. For example, if the temperature of earth was 360 degrees celsius, no life would be able to survive as it would be too hot. For this reason, he believes that by studying the gasses that made up the atmosphere and finding the average temperature of any planet, he would be able to determine if life would be able to exist on that planet.

James Lovelock started to look at the atmosphere and the temperature of the earth and began to contemplate that perhaps the atmosphere shows not only the signs of life, but that the life on earth influences parts of the atmosphere and regulates the temperature to help create the conditions neccesary for the earths survival.

Plants and animals together help maintain the levels of both carbon dioxide and oxygen at a somewhat constant level which in turn helps keep the temperature at a somewhat constant level, and this allows them to both survive. According to Lovelock, living things seem to regulate the composition of the atmosphere to ensure their own survival.

Gases in the atmosphere consist of:

Oxygen, which is put in the air by plants during photosyntesis. Plants absorb carbon dioxide and use the carbon to grow and give off oxygen. If the oxygen on the earth rises above 25%,fire would burn very quickly that big areas of land would be completely destroyed and plants would not be able to grow.

Methane. This gas is produced in the guts of living animals as they digest their food. The fact that even small amounts of methane can be detected in any atmosphere will indicate the presense of life.

Ozone. Ozone is a type of oxygen and is a greenhouse gas. It forms a layer around the earth that protects it from harmful ultraviolet rays.

IMPLICATIONS

The Gaia theory shows that everything in the world has a role and depends on other elements around them. For example, if animals are all killed, then we are losing a majour source of producing methane, therefore we are effecting the way the world works. We as humans are disrupting this system, by producing many fossil fules, and by cutting down trees in large numbers, and not planting more trees to make up for them.