Iron: The Element That Connects the Universe, Life, and Civilization

Iron occupies a unique place across the history of matter, from its formation in stars to its roles in planets, living systems, and human technology. Its nuclear properties help explain the accumulation of iron-group nuclei during stellar nucleosynthesis, while its abundance, redox chemistry, and coordination properties shape its behavior in rocky planets and surface environments. On Earth, Fe(II)/Fe(III) chemistry influences mineral formation, ocean chemistry, oxygenation, and the evolution of life. In living systems, iron supports electron transfer, catalysis, oxygen transport, respiration, photosynthesis, and DNA synthesis, while its redox activity also creates a risk of oxidative damage. Humans later learned to extract, refine, alloy, and shape iron, making it central to agriculture, infrastructure, transportation, and industry. Modern chemistry and materials science have extended this control to catalysts, magnetic nanomaterials, electrochemical systems, and environmental technologies. This review follows iron across these scales and examines how its fundamental properties, and the ability to control them, have allowed the element to remain important from the formation of stars and planets to life, metallurgy, and modern technology.