A new synthesis argues Earth’s oxygen-richer air wasn’t driven by one event, but by a long geological sequence: the supercontinent Columbia, early lower-temperature subduction, and later plate “plumbing” that favored cold subduction. The key idea is that more
Earth’s oxygen-rich atmosphere may owe a lot to something almost nobody thinks about when they take a breath: what happened to carbon when tectonic plates pulled it down.
The argument begins with an early “supercontinent” called Columbia, sometimes compared to Pangaea. With a substantial amount of land above sea level. erosion could deliver enough nutrients to the oceans to support large numbers of photosynthetic cyanobacteria. Evidence for that kind of world, the researchers point to, shows up in seafloor sedimentary rocks rich in organic carbon.
After Columbia formed, its breakup lines up with the first signs of lower-temperature subduction. That cooler kind of plate diving would have made it easier for more organic carbon—and carbonate accumulating in shallow water around Columbia—to be subducted deep into the mantle.
Then came what geologists often call the Boring Billion. when mantle convection and tectonic plate movement appear to have slowed down. But once the planet moved toward the later formation and breakup of the supercontinents Gondwana and Pangaea. the tectonic picture begins to look more like the present: a world where plate boundaries include lots of low-temperature subduction.
On today’s Earth, the “Ring of Fire” around the Pacific Ocean points to how that works in practice. It marks a vast subduction zone that continuously carries carbon- and sulfur-rich sediments deep into the mantle. The researchers’ claim is that once this sort of cold subduction became common. the balance of Earth’s oxygen could tilt more toward the atmosphere.
The story doesn’t pretend oxygen has a single cause. The researchers describe it instead as a chain of interactions across biology and geology—processes that. in their words. “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.”.
Put another way: the oxygen-rich sky depended not just on producing life in the ocean. but on what the planet did with the carbon and sulfur life helped store. If subduction grew more efficient at pushing those materials downward as Earth cooled. less carbon stayed available to counterbalance the rise of oxygen.
The researchers also note there is more to the story beyond these headline steps—covering biology and geology—but the paper anchors its case to that baseline flux of carbon (and sulfur) shaped by cold subduction. The study was published in PNAS in 2026, with DOI 10.1073/pnas.2534056123.
oxygen-rich atmosphere cold subduction carbon sulfur flux cyanobacteria Columbia supercontinent Gondwana Pangaea Ring of Fire Earth oxygen balance mantle convection tectonic plates