The iron of the Mesabi
The ore that built American steel, laid down by bacteria
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The Mesabi Range in Minnesota is a ridge of iron-bearing rock, formed on a sea floor around 1.9 billion years ago. The Mesabi Range supplied the bulk of the iron ore for American steel from the 1890s and through both world wars. The connection is worth registering: a biological event in the Precambrian determined where twentieth-century industrial power could be built. The richest haematite ores were exhausted by about 1950, and the industry moved to taconite, a leaner rock that has to be concentrated.
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When the first organisms began making oxygen, it reacted with iron dissolved in the sea. The iron rusted and sank to the bottom, layer upon layer, over millions of years. Those layers became vast iron deposits — and they are why Minnesota could supply the steel for American industry.
Sources
- Minnesota Geological Survey: Biwabik Iron Formation
- Lyons, Reinhard & Planavsky, Nature 506 (2014)
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