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The Atmosphere

What are the Gases of the Atmosphere Today?

The atmosphere today has evolved from the changes
described in the previous five pages.

For the past 200 million years the amounts of the different
gases in the air have been almost the same as they are today.

The approximate composition of the air today is

Gas Proportion
Nitrogen (N2) 78%
Oxygen (O2) 21%
Argon (Ar) 0·9%
Carbon Dioxide (CO2) 0·04%
Other Noble Gases small amounts
Water Vapour (H2O) Variable

The proportion of carbon dioxide in the air
has risen from 0·03% to 0·04% in the last hundred years
because of the burning of fossil fuels.

The amount of water vapour in the air varies
with temperature and weather - see the water cycle.

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