For food, Archaea probably consumed naturally occuring amino
acids. Amino acids, sugars, and other organic compounds
formed spontaneously in the atmosphere then dissolved in liquid water. Upon digesting these molecules, early bacteria produced methane and carbon dioxide as waste products. Fermenting bacteria would be an example from today of what these early creatures might have been like. To make beer you put barley or wheat with water. The broken down barley and wheat turns into sugar. Fermenting bacteria eat the sugars and produce alcohol and carbon dioxide gas as waste products. Beer manufacturers then remove the bacteria and carbon dioxide, and put the alcohol in bottles. In the early Earth, the alcohol and carbon dioxide became part of the natural environment.
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