The beginning of the story, they say, may be the assembly of an early “supercontinent” (presumably Pangaea). Colombia. With appreciable amounts of land above sea level, erosion can provide enough nutrients for the oceans to support large amounts of photosynthetic cyanobacteria. We can see evidence of this in the organic carbon-rich seafloor sedimentary rocks.
Columbia breakup coincides with the first signs of low-temperature subduction. This would allow more of this organic carbon and the carbonate accumulated in the shallow water around Columbia to sink deeper into the mantle.
Then comes the drilling billion, even when mantle convection and tectonic plate movement seem sluggish. But then, the formation and breakup of the supercontinents Gondwana and Pangea lead us to a map of tectonic plate boundaries similar to our present world, with lots of low-temperature subduction.
For example, the “Ring of Fire” around the Pacific Ocean today indicates a giant subduction zone that continuously transports carbon- and sulfur-rich sediments deep into the mantle. Once this kind of subduction became common, Earth’s oxygen balance could tilt more toward the atmosphere.
Of course, there is more to the story, both in terms of biology and geology. Our oxygen-rich atmosphere is the product of rich interactions. However, the researchers write: “These processes all operated on a baseline defined by a net flux of carbon (and sulfur) between Earth’s interior and exterior, which we argue was driven by the evolving efficiency of cold subduction in a cooling Earth.”
PNAS, 2026. DOI: 10.1073/pnas.2534056123 (About DOIs).
