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Early in the Earth's development, the atmosphere contained no oxygen. Yet the iron dissolved in the oceans was oxidized in gigantic quantities and deposited as rock. It can be seen today, for example, as banded iron ore in South Africa.

A new study investigates how various bacteria excrete insoluble iron as part of their metabolic processes. Some—the phototrophic iron oxidizers—gain energy by oxidizing the iron with the help of sunlight, and others by reacting the iron with nitrate as an oxidizing agent.

An international research team including Dr. Casey Bryce from the University of Bristol and Dr. Verena Nikeleit and Professor Andreas Kappler, geomicrobiologists at the University of Tübingen, examined these processes and asked: Which microbes had the upper hand in the competition for the iron? The rival bacteria also used nitrogen monoxide, a toxic gas.

The study has been published in the journal Nature Geoscience.

Two to three billion years ago, the composition of the Earth's atmosphere was completely different.

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