Why would glycolysis and fermentation be considered older processes in the history of life than the electron transport system and the citric acid cycle?

Answer 1

Glycolysis and fermentation are considered older processes in the history of life because they do not require oxygen and can occur in anaerobic environments, which were predominant on early Earth. These pathways likely evolved first as primitive organisms needed to generate energy without the presence of oxygen, which became more abundant later due to photosynthetic activity. In contrast, the electron transport system and the citric acid cycle depend on oxygen and more complex cellular machinery, suggesting they developed after the advent of aerobic respiration. Thus, glycolysis and fermentation represent fundamental metabolic pathways that predate the more advanced energy extraction methods.