Explanation:
Primordial organisms did not require oxygen for respiration as is the case with most organisms case today. These organisms were and are still mainly anaerobic. They main form of cellular respiration is glycolysis that does not utilize oxygen. Since other organisms evolved from the primordial cells, it is deduced that the early atmosphere was not mainly composed of oxygen but mainly carbon dioxide.
In today’s aerobic cells oxygen is utilized in the Krebs cycle as a proton acceptor making cellular respiration even more efficient in the production of energy. Remember that, utlimately, organisms evolve to fit into their environment.
Learn More:
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