Deep-Earth Magma Can Store Hidden Oxygen, Study Finds

After rapidly cooling the melt into glass, the team measured its composition and calculated how much oxygen was needed to balance the other elements, together with the oxygen locked in water and carbon dioxide. Whatever remained unaccounted for they called "excess oxygen."

The results showed a clear pattern:

• At atmospheric pressure, the glass held almost no excess oxygen.
• At 7 gigapascals, excess oxygen exceeded 5% of the sample's weight.
• Control experiments without added platinum oxide yielded only 0.2% to 0.5% by weight.

Raman spectroscopy (a technique that identifies substances by how they interact with light) found no signature of oxygen gas in the glass, indicating the oxygen had entered the material's structure rather than forming trapped bubbles. Some oxygen may even have escaped during cooling, so the true storage capacity could be higher.

What did the computer simulations show?

Prof. Niu led theoretical simulations using deep neural network models, which approximate the accuracy of ab initio calculations — descriptions of atomic behavior based on quantum mechanics. Although the simulated system contained only magnesium, silicon and oxygen, it reproduced the experimental trend: oxygen storage rose with pressure.

The models revealed that as more oxygen entered the melt, the electrical charges on oxygen atoms became more varied, and a small fraction formed peroxide-like bonds, in which oxygen atoms bond to each other. These changes help explain how molten rock accommodates oxygen beyond conventional chemical predictions. The behavior mirrors that of water and carbon dioxide, which also grow more soluble in magma as pressure increases.

The researchers propose that oxygen should now be recognized as an independent component of silicate melts.

Could ancient volcanoes have oxygenated the atmosphere?

The discovery points to a possible mechanism linking Earth's interior to its air. Magma forming in oxidized regions of the mantle could absorb excess oxygen under immense pressure, then release it as it rises and pressure falls, gradually increasing the oxidation (electron-transfer processes) of the upper mantle, crust and atmosphere.

The timing is suggestive. Between roughly 2.5 billion and 2.0 billion years ago, atmospheric oxygen rose sharply — an interval overlapping the formation of some of Earth's largest large igneous provinces, vast regions of rock created by enormous magma outpourings.

The team's preliminary calculation illustrates the potential scale: if magma erupted during that period released excess oxygen equal to just 0.27% of its weight, the total could theoretically match all the oxygen in today's atmosphere. The researchers stress this does not prove volcanoes supplied that oxygen; it shows how a small fractional release from immense magma volumes could have planetary consequences.

What comes next?

The findings may reshape models of ancient magma oceans — molten regions thought to have existed during the early evolution of rocky planets — and add a new factor to volcanic degassing, the process by which gases escape molten rock. The work may also aid the study of habitable environments beyond Earth, though much remains uncertain about how much oxygen natural magmas carry and how much reaches the surface.

Some of the processes behind Earth's breathable air, it seems, may have begun far beneath our feet.