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How great was the Great Oxidation Event?
Geochemical sleuthing amid acid mine runoff suggests that scientists should rethink an isotope signal long taken to indicate low levels of atmospheric oxygen in Earth’s deep past.
The composition of these waters is considered extreme today, yet the sort of acid rock drainage that causes these conditions was widespread long ago, when newly available atmospheric oxygen first began interacting with sulfur minerals on land. A critical transition in our planet’s history occurred when the single-celled ancestors of plants learned to combine carbon dioxide and water—two chemicals found everywhere on Earth—to make their cells and produce energy. Spain’s Rio Tinto flows roughly 100 kilometers through the southwest of the country, stained blood red from its headwaters north of the town of Nerva in the Sierra Moreno to its mouth at the Ria of Huelva estuary, where it spills into the Atlantic Ocean.
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