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Hydrogen was the main chemical component of the primitive atmosphere. With the creation of life and evolution of photosynthesis by plants, oxygen started to appear as an increasing chemical component of the atmosphere.
In the last century, carbon dioxide, increased in the atmosphere of the earth from 290 parts per million to 330 parts per million. The increase is due directly to activities like the burning of fossil fuels and worldwide destruction of forests.
There are two main changes in the composition of the atmosphere which are caused by changes in the biosphere.
1.- The expansion of atmospheric oxygen which is due to the increase in plant mass and photosynthetic activity. This constitutes the clearest example of a vital change in the chemistry of the atmosphere directly caused by an alteration in the biosphere.,
2.- The changes in atmospheric carbon dioxide, which represents an alteration in the chemistry of the atmosphere, caused mainly by human activities as mentioned above and respiration by-products.
These two examples demonstrate that the chemistry of the atmosphere could be seriously altered from the earth's surface by human interference.
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