Earth’s ‘Great Oxidation Event’ was spread over 200 million years, according to recent geochemical discoveries

About 2.5 billion years ago, free oxygen, or O2, first started to accumulate to meaningful levels in Earth’s atmosphere, setting the stage for the rise of complex life on our evolving planet. About 2.5 billion years ago, free oxygen, or O2, first started to accumulate to meaningful levels in Earth’s atmosphere, setting the stage for the rise of complex life on our evolving planet. Earth Sciences Environment Phys.org – latest science and technology news stories