The best scenario for the origin of life is that it first arose in hydrothermal vents deep in the ocean. The first catalysts of metabolic reactions were metals and later on simple organic molecules bound to metals. The substrates for all reactions were inorganic compounds such as H2, CO2, NH3, H2S and phosphate/phosphite.
Over time, the inorganic catalysts were gradually replaced by protein and RNA catalysts that often incorporated the metal ions into their active sites or used cofactors containing metal ions. There are about 400 basic metabolic reactions that are fundamental to life. Some enzyme catalysts are very ancient but others seem to be more recent.
