How oxygen enriched Earth's atmosphere 2.5 billion years ago

Cyanobacteria, as they still exist today, were the first organisms to carry out photosynthesis and release oxygen. Produced in primeval oceans about 2.5 billion years ago, this oxygen accumulated in Earth's atmosphere on an immense scale. A research team led by University of Tübingen geomicrobiologist Professor Andreas Kappler has used laboratory experiments to investigate how this process was even possible, given that the iron dissolved in ocean water strongly inhibited the growth of cyanobacteria.