Researchers led by Yanhao Lin and Ho-kwang Mao tested synthetic basalt and found that samples prepared under higher pressure contained more excess oxygen when the molten rock had an added oxygen source, according to a Science China Press account published Oct. 23, 2026, by SciTechDaily. Their study appeared Aug. 25, 2026, in National Science Review; Haiyang Niu and Wim van Westrenen also worked on it. The team proposes that magma rising from oxidized regions of Earth's mantle could release oxygen as pressure falls. The laboratory tests did not measure a release from ancient eruptions.
The team added platinum oxide as an oxygen source to synthetic mid-ocean-ridge basalt. They melted it at 1,200 to 1,800 degrees Celsius, at pressures ranging from 1 atmosphere to 7 gigapascals, then cooled the samples into glass. To calculate “excess oxygen,” they accounted for oxygen needed to balance other elements, as well as oxygen in water and carbon dioxide. In runs with platinum oxide, excess oxygen was close to zero at 1 atmosphere but exceeded 5% of sample weight at 7 gigapascals. Runs without platinum oxide yielded 0.2% to 0.5% excess oxygen by weight, the account reports.
Raman spectroscopy detected no signature of oxygen gas in the glass, which the account says indicates the excess oxygen was incorporated into the glass rather than trapped in gas bubbles. It also cautions that some oxygen may have escaped as the samples cooled.
The team suggests that falling pressure during magma's ascent could reduce how much oxygen it can retain. They propose that this process may help explain an overlap between atmospheric oxygen increases roughly 2.5 billion to 2 billion years ago and the formation of some large igneous provinces. Their rough estimate is conditional: If magma erupted during that period released excess oxygen equal to 0.27% of its weight, it could have supplied as much oxygen as today's atmosphere contains. The experiments did not establish that ancient eruptions released that oxygen or caused the atmospheric increase.
