CHENGDU — A new study led by Wei Shi of Chengdu University of Technology links shifts in tectonic plate subduction to major increases in Earth’s atmospheric oxygen over geologic time. The research, published in the Proceedings of the National Academy of Sciences (PNAS) in 2026, identifies a correlation between cooler subduction zones and three key oxygenation events in Earth’s history.

Earth’s atmosphere gained oxygen in three main pulses: the Great Oxygenation Event between 2.4 and 2.0 billion years ago, a second rise from 800 to 500 million years ago, and a third increase from 450 to 250 million years ago that established modern oxygen levels. The study notes that lower-temperature subduction occurred between 2.2 and 1.8 billion years ago and again over the past 800 million years—periods that align closely with these oxygenation phases.

The interval between 1.8 billion and 800 million years ago, often called the “Boring Billion” for its apparent lack of major geological and biological change, corresponds with a lack of cool subduction and minimal oxygen increase. According to the study, the assembly of the supercontinent Columbia enabled erosion that delivered nutrients to oceans, fueling photosynthetic cyanobacteria and leaving behind seafloor sedimentary rocks rich in organic carbon. The subsequent breakup of Columbia coincided with the emergence of lower-temperature subduction, which allowed more organic carbon and carbonate to be carried deep into Earth’s mantle.

Later, the formation and breakup of the supercontinents Gondwana and Pangaea gave rise to modern-style tectonic boundaries featuring extensive low-temperature subduction zones. The study highlights that today’s Pacific “Ring of Fire” continues this process by transporting carbon- and sulfur-rich sediments into the mantle. When Earth’s mantle was hotter in earlier eons, subducted carbon and sulfur were released back into the shallow mantle and returned to the atmosphere through volcanoes, where they reacted with oxygen. In cooler mantle conditions, however, these elements are retained at greater depths, reducing their interaction with atmospheric oxygen.

“Researchers argue that the net flux of carbon and sulfur between Earth’s interior and exterior, controlled by the efficiency of cold subduction on a cooling Earth, defined the baseline for atmospheric oxygenation.” The paper carries the DOI 10.1073/pnas.2534056123.