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The original was posted on /r/todayilearned by /u/Dromeoraptor on 2024-09-19 22:39:48+00:00.

Original Title: TIL that over 60% of global iron reserves and most of the iron ore currently mined were created by precambrian bacteria. These cyanobacteria caused the Great Oxygenation Event, where free oxygen became much more common on Earth. Some of this oxygen combined with iron to form banded iron formations.