Molten rock deep inside the Earth can carry far more oxygen than textbook chemistry allows, according to experiments led by Yanhao Lin and Ho-kwang Mao at the Center for High Pressure Science and Technology Advanced Research in China. At a pressure of 7 gigapascals, their synthetic basalt melt held more than 5 percent excess oxygen by weight. If magma like that rose and released its load, it could have helped lift atmospheric oxygen to breathable levels, though the authors stop well short of saying it did.
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Earth’s air was not always breathable. For roughly the first two billion years, free oxygen in the atmosphere was scarce. Then, between about 2.5 and 2.0 billion years ago, it rose sharply in what geologists call the Great Oxidation Event. The standard explanation credits photosynthesizing microbes, which release oxygen as waste, with a long delay before the gas accumulated because rocks and volcanic gases soaked it up as quickly as it appeared. A long-standing puzzle is why the rise came when it did and how the planet’s interior, which can absorb or release oxidizing material, took part in the story.
Oxygen as a dissolved ingredient of melt
Geochemists have long treated the oxygen in a silicate melt as fixed by its metals. Each atom of silicon, iron or magnesium bonds with a set number of oxygen atoms, and anything left over was assumed to be negligible. The team behind the paper in National Science Review challenges that assumption. Their results indicate that melts can hold oxygen beyond those valence limits, and that this “excess oxygen” behaves as a volatile component, dissolving under pressure and coming out as the melt decompresses.
The authors define excess oxygen as what remains after balancing the other elements and accounting for the oxygen in water and carbon dioxide. They propose treating oxygen as an independent component of silicate melts, which would change how models of magma chemistry are set up. The study, titled “Magma as a carrier of non-stoichiometric oxygen linking Earth’s interior and atmosphere,” was published on August 25, 2026, and Lin is its corresponding author.
The experiments under pressure
Using piston-cylinder and cubic presses, the researchers heated a synthetic mid-ocean ridge basalt at pressures from ordinary atmospheric pressure up to 7 gigapascals and temperatures between 1200 and 1800 degrees Celsius. They added platinum oxide to create an oxygen-rich environment, quenched each melt into glass and measured its composition. The excess oxygen was near zero at atmospheric pressure and climbed to 5.2 percent by weight at 7 gigapascals. Control runs without the added oxygen source reached only 0.2 to 0.5 percent, as reported in ScienceDaily’s summary of the work.
Raman spectroscopy found no signature of oxygen gas in the glass, so the extra oxygen appears to be built into the melt’s structure rather than trapped in bubbles. Computer simulations led by Haiyang Niu of Northwestern Polytechnical University used a neural-network model of a simplified magnesium-silicon-oxygen liquid and reproduced the rising trend with pressure, giving 0.33 percent at atmospheric pressure and 2.12 percent at 9 gigapascals. In those simulations, oxygen took on more varied charge states and a small fraction formed peroxide-like oxygen-oxygen bonds. Wim van Westrenen of Vrije Universiteit Amsterdam is among the co-authors.
From melt to atmosphere, with the caveats attached
The atmospheric link comes from a first-order scaling exercise. If large igneous provinces, the enormous outpourings of basalt that built up around 2.5 to 2.0 billion years ago, released just 0.27 percent of the magma’s weight as oxygen, the total could in principle match the oxygen in today’s atmosphere. The authors describe this as a scale check, not a model of how the atmosphere actually evolved, and it depends on assumed volumes, thicknesses and the ratio of erupted to buried magma.
The authors are explicit about the limits. They state that the work does not establish that volcanic activity actually supplied that much atmospheric oxygen, and that further research is needed to find out how much oxygen natural magmas carry. The platinum oxide imposed unusually oxidizing conditions, so the results show what a melt can hold under oxygen-rich conditions, not what typical mantle magma contains. Not all mantle-derived magmas are expected to carry significant excess oxygen.
The measured values may also be too low. Some oxygen could have escaped as the samples cooled, no experiment appears to have reached saturation, and the simulations returned smaller numbers than the experiments, which the authors attribute to their simplified model. The group says the kinetics need study with measurements taken while the melt is under pressure.
That leaves a clear open question for the field, one that the HPSTAR group, Northwestern Polytechnical University and Vrije Universiteit Amsterdam collaborators have framed but not answered: how much excess oxygen do real magmas from the mantle actually carry? Until measurements on natural samples settle it, deep magma is a candidate contributor to breathable air, in the authors’ words a possible link and not a demonstrated one.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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