A general presentation of the type of metals present in living systems, the wide variety of structures of metallic active sites, and the reactivity of these metal ions (Lewis acidity, redox properties, etc.) was proposed.
Secondly, it was shown that there was an excellent correlation between the type of metal ion used for a given biological function and, on the one hand, the abundance of the element, in soluble form, on the earth's surface and, on the other, its intrinsic physico-chemical properties (for example, Zn for hydrolysis reactions and iron and copper for redox reactions). It is highly probable that life on earth was only possible thanks to the exploitation of the chemical potential of these metals. A reasonable hypothesis, which runs counter to S. Miller's (1953) vision of a heterotrophic origin of life, is that of an autotrophic origin using atmospheric molecules such as nitrogen, carbon dioxide and carbon monoxide, and heterogeneous catalysts/reducers such as nickel and iron sulfides, in the absence of oxygen to produce amino acids and peptides. These catalysts have been remarkably conserved over the course of evolution. This original period can be described as the " iron age ", which lasted 2 billion years, considering the importance of this metal in biological chemistry and its abundance on the earth's surface.
Then, the arrival of oxygen led to massive iron oxidation, precipitation and a drastic change in the chemical environment of life. The oxidation of copper, for example, made it more soluble and available, and numerous copper enzymes were invented (" copper era ").
