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Since the source of atmospheric oxygen is
conversion of carbon dioxide to oxygen by plants, the sum of oxygen + carbon
dioxide remains constant. It is hard to comprehend how
oxygen levels could have ever been much higher than at present. The
present steady state level of carbon dioxide, .04%, [the
same figure I learned in school over 60 years ago] is fine
tuned by the negative feedback effect of elevated carbon dioxide
stimulating photosynthesis.
If things get imbalanced by destruction of
forests, eventually the present steady state could no longer be maintained
and carbon dioxide would rise. However in order for oxygen levels to
diminish by a tenth to ca. 19%, carbon dioxide must increase to
2.04% or 50
fold. Bert
Pressman
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