Fig. 4.

Time line of an iron-centric view of development and evolution of life on Earth. Mantle iron content and surface water retention are governed by early planetary accretion events, including distance from the sun and prevailing redox conditions. Initiation of foundational biochemical processes may have been facilitated by co-occurrence of native, ferrous, and ferric iron at hydrothermal vents or subaerial wet land. Oxygenic photosynthesis depleted oceanic iron, favoring deployment of Fe³⁺-capturing siderophores from bacteria. Complex social, endosymbiotic, predatory, infectious, and multicellular behaviors allow more efficient utilization, or appropriation, of relatively scarce iron. Host–pathogen relationships are strongly influenced by iron availability, selecting genetic variants. TCA, tricarboxylic acid cycle.