Iron in evolution.

Iron chemistry in the environment and in organisms is entwined. The iron surface minerals in solution for the first billion years of the planet were ferrous compounds. This ion became and has remained a major participant in organisms. The evolution of iron was due to its oxidation to insoluble ferric ions by oxygen released from organisms. The evolution of cellular iron chemistry then required uptake from this oxidised state. Use was expanded from the mainly electron transfer properties in the original reductive cell interior to employment in external oxidative chemistry. The environment/organisms evolution is that of one predictable chemical system.