On Earth, microbes began producing oxygen long before it accumulated in the atmosphere during the Great Oxidation Event (GOE) around 2.4 billion years ago. So why the delay? Producing oxygen wasn’t enough—something in Earth’s environment had to change to let it build up.

One possibility lies deep within the planet. Gases from Earth’s mantle—its rocky interior—may have slowly become less oxygen-poor over time, due to gradual mixing of chemically distinct layers formed early in Earth’s history. This slow shift could have allowed atmospheric oxygen to rise over time.

We use 3D computer models to test this idea, exploring how different rates of mixing inside Earth could have affected the history of oxygen availability at the surface. If mixing happens too slowly on other planets, oxygen-making life could evolve without ever creating an oxygen-rich atmosphere—limiting the chances for complex or intelligent life to emerge.

Understanding these deep-Earth processes can help us better predict which exoplanets might host truly Earth-like biospheres—and life like us.