Ancient microbes may have used oxygen 500 million years before it filled Earth’s atmosphere

Today, oxygen is essential to life and constantly present in the air we breathe. But for most of Earth's early history, that was not true. Oxygen did not become a stable part of the atmosphere until about 2.3 billion years ago, during a transformative period known as the Great Oxidation Event (GOE). That shift permanently altered the planet and paved the way for oxygen breathing organisms to evolve and thrive.

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