Biologists believe that Earth's early life-forms were exposed to an atmosphere that had no molecular oxygen and therefore had not yet evolved the Krebs cycle.If so,alcoholic fermentation would have been particularly critical to life,because without this pathway

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Without the Krebs cycle, carbon could not be recycled back into the biosphere for use by producers. Alcoholic fermentation produces ethanol, which can be used as a nutrient for other consumers, but the accumulation of lactic acid and the source of NADH for electron transport are not directly related to the importance of alcoholic fermentation in the absence of the Krebs cycle.

Biologists Believe That Earth's Early Life-Forms Were Exposed to an Atmosphere