Tuesday, October 27, 2009

Atmosphere

WHAT IS THE ATMOSPHERE?
The earth's atmosphere is of immense importance to human beings. The atmosphere is a layer of a mixture of gases enveloping the earth, held to it by gravitation force. Almost all of the atmosphere (97 per cent) lies within 29 km of the earth's surface. The upper liqrit of the atmo­sphere can be drawn approximately at a height of 10,000 km. Beyond about 100 km, recent data from satellites suggest that the lightest gases separate out, forming several concentric layers around the earth.

The innermost of these is the nitrogen layer (between 100-200 km); then comes oxygen (200-1100 km); helium (1100-3500 km) and then hydroge~ only, to which there is really no clearly defined upper limit~ The composition of gases remains more or less constant in the lower layers of the atmosphere, though its temperature and pressure may vary in time and place. This composition commonly known as 'air' tends to act as a single gas. About 99 per cent of dry air is constituted by oxygen and nitrogen. Carbon dioxide, though apparently a minor gas, is important due to its ability to absorb heat, enabling the layers of the atmosphere to be warmed up.

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