About 2.4 billion years ago, at the end of the Archean Eon, a planet-wide increase in oxygen levels called the Great Oxidation Event (GOE) created the familiar atmosphere we all breathe today. Researchers focused on life’s origins widely agree that this transition event was caused by the global proliferation of photosynthetic microbes capable of splitting water to make molecular oxygen (O2). However, according to Tanja Bosak, associate professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS), researchers don’t know how long before the GOE these organisms evolved.
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Source: Phys.org