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The earths early atmosphere was formed by volcanic activity
scientists think the atmosphere mainly consisted of carbon dioxide, there may also have been nitrogen and water vapour together with traces of methane and a mmonia
as plants spread over the earth the levels of oxygen increased
photosynthesis by algae and plants reduced the percentage of carbon dioxide in the early atmosphere
the formation of sedimentary rocks and fossil fuels that contain carbon also removed carbon dioxide from the atmosphere
which brings us to today where our atmosphere is 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, 0.04 percent carbon dioxide, and then trace amounts of other gases
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