The beginning of the story, they say, could be the assembly of an early “supercontinent” (think Pangaea) called Columbia. With an appreciable amount of land above sea level, erosion could deliver enough nutrients to the oceans to support a large amount of photosynthetic cyanobacteria. We can see the evidence of this in seafloor sedimentary rocks rich in organic carbon.
The breakup of Columbia aligns with the first signs of lower-temperature subduction. That would have enabled more of this organic carbon—and carbonate accumulating in shallow water around Columbia—to be subducted deep into the mantle.
Then comes the Boring Billion, when even mantle convection and tectonic plate movement seem to have been sluggish. But after that, the formation and breakup of the supercontinents Gondwana and Pangaea move us toward a map of tectonic plate boundaries that looks like our present world, with lots of low-temperature subduction.
The “Ring of Fire” around the Pacific Ocean today, for example, marks a huge zone of subduction that continuously carries carbon and sulfur-rich sediments deep into the mantle. Once this sort of subduction became common, the balance of Earth’s oxygen was able to tilt more toward the atmosphere.
There certainly is a lot more to the story, both in terms of biology and geology. Our oxygen-rich atmosphere is the product of a rich set of interactions. But, the researchers write, “These processes all operated on top of the baseline defined by the net flux of carbon (and sulfur) between Earth’s interior and exterior, which we argue was controlled by the evolving efficiency of cold subduction on a cooling Earth.”
PNAS, 2026. DOI: 10.1073/pnas.2534056123 (About DOIs).
