Over the course of hundreds of millions of years, prokaryotic microbes evolved to form a global metabolic network.  That network is based on electron transfer reactions with and without protons.  The responsible enzymes, the oxidoreductases, encoded by only 400 core genes, literally have evolved to become a planetary electrical circuit powered by solar energy.  Microbial metabolism inevitably leads to gas exchanges between the organisms and the environment.  The gases can, over long geological time scales, lead to changes in the composition of planetary atmospheres.  Indeed, the atmosphere and oceans on Earth effectively are “wires” that connect metabolic processes across the globe.  A structural analysis of the oxidorectases reveals that they arose from a very small subset of protein folds.  We have identified two of the core folds, the “Legos” of life, and I will discuss how these very simple protein motifs evolved early in Earth’s history to create an extremely robust global metabolic circuit.