Most iron (and steel) comes from iron ore formations which are at least 1 billion, and up to 3 billion years old: banded iron formations (BIFs). The oldest of

Most iron (and steel) comes from iron ore formations which are at least 1 billion, and up to 3 billion years old: banded iron formations (BIFs). The oldest of those are literally legacies of the first major burst of biological activity on Earth, which released oxygen into the atmosphere, which for most of a billion of years or so resulted in reducing unoxidized minerals, particularly iron, in the Great Rusting.