Iron

Iron-56 sits at very nearly the peak of the binding-energy curve, which is why a massive star fuses its way up the periodic table and then stalls: past iron, fusion consumes energy rather than releasing it, the core collapses and the supernova that follows forges everything heavier. Every iron atom in your haemoglobin came out of a star that ran out of profitable fuel. Humans worked meteoritic iron long before they could smelt ore — the dagger buried with Tutankhamun has a nickel content that marks it unmistakably as meteoritic. The Earth's core is mostly iron-nickel, and its convection generates the magnetic field that keeps the solar wind from stripping the atmosphere. Around 1.9 billion tonnes of crude steel are produced each year, more than all other metals combined by a wide margin.