Formation
Most of the world's iron ore, including that contained in the Mesabi Iron Range, was formed during the middle Precambrian period. During this period, erosion leveled mountains. This erosion released iron and silica into the waters of a new sea. Marine algae living in this new sea raised the level of atmospheric oxygen. This oxygen catastrophe caused the eroded iron to precipitate into the banded iron formations found in the Mesabi Iron Range and other members of the Animikie Group.
Read more about this topic: Mesabi Range
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