Why is iron so important to life on Earth?

The answer

Iron is critical for nearly all life because it sits at the heart of hemoglobin, the molecule that transports oxygen in your blood. Its ability to easily switch between two oxidation states (Fe²⁺ and Fe³⁺) makes it perfect for electron transfer reactions essential to cellular respiration. Iron is also the heaviest element that can be produced by nuclear fusion in massive stars - creating heavier elements requires the energy of a supernova. Every iron atom in your body was literally forged in the core of a star that exploded billions of years ago.