Ask A Scientist© Molecular Biology Archive

name         Mike D.
age          14

Question -   According to the heterotrophic hypothesis, autotrphs
developed after the evolution of heterotrophs partly because the primitive
environment of the earth lacked - was it carbon dioxide?
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The primitive atmosphere lacked oxygen.  Oxygen didn't appear until plants
began to photosynthesize.  There is no evidence of plants or cyanobacteria in
the fossil record before about 2 billion years ago.  Also rocks containing
oxides (elements combined with oxgyen) don't appear until then either.

vanhoeck
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Autotrophs need a carbon source and photosynthesis does utilize carbon dioxide
for this reason.  Photoheterotrophs and other heterotropic organisms may have provided the 
carbon that allowed for photosynthesis to evolve.  Of course, all this is hypothetical.

Steve Sample
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