Here’s a new spin on how Earth became an oxygen-rich planet: As our planet’s rotation slowed, microbes were bathed in longer stints of sunlight that revved up their release of oxygen into the atmosphere.

Every breath you take is possible because billions of years ago, dense mats of cyanobacteria — the first life on Earth — began churning out oxygen as a byproduct from photosynthesis. But scientists still didn’t know for sure what triggered two transformative oxygenation events that turned Earth from a low-oxygen planet into an oxygen-rich world where complex organisms could evolve and diversify.