The ocean rusts
Almost all the iron we use was laid down in this period
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Banded iron formations consist of alternating layers of iron oxide and silica, often millimetres thick, deposited over hundreds of millions of years. They are the physical receipt for oxygenation: as long as the ocean held dissolved ferrous iron, any oxygen was bound up immediately. When the iron ran out around 1.85 billion years ago, the great deposits ceased — and only then could oxygen build up in the atmosphere in earnest. The Hamersley province in Australia and Kryvyi Rih in Ukraine are among the largest occurrences. The entire age of steel rests on a biological waste product.
For children
The early ocean was full of dissolved iron. When bacteria began making oxygen, the two reacted and the iron sank to the bottom as rust — layer upon layer, for hundreds of millions of years. Almost all the iron in bridges, cars and ships comes from those layers.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org