The study, published in the journal National Science Review, suggests that magma under extreme pressure can absorb additional oxygen beyond what its usual chemical composition would predict.

The findings could help scientists better understand how Earth’s interior, volcanic activity and atmosphere have interacted over geological time.

The research was led by scientists from the Center for High Pressure Science and Technology Advanced Research in China, working with colleagues from Northwestern Polytechnical University and Vrije Universiteit Amsterdam.

To investigate the process, the team recreated conditions found deep inside Earth in laboratory experiments.

They heated a synthetic form of mid-ocean ridge basalt, a volcanic rock, at temperatures between 1,200 and 1,800 degrees Celsius and pressures reaching seven gigapascals.

At the highest pressure, the material contained more than five per cent excess oxygen by weight when platinum oxide was added to create an oxygen-rich environment.

Samples tested under similar conditions without the added platinum oxide contained much lower amounts, between 0.2 and 0.5 per cent.

The researchers used Raman spectroscopy to check whether the extra oxygen was present as trapped gas bubbles.

They found no detectable evidence of oxygen gas, suggesting that the additional oxygen had become part of the glass structure formed when the molten samples cooled.

Computer simulations supported the experimental findings, showing that magma’s capacity to hold excess oxygen increases with pressure.

The models also suggested that oxygen atoms can form different chemical arrangements as more oxygen enters the melt.

The team proposes that magma formed in oxidised parts of Earth’s mantle could absorb extra oxygen deep underground.

As magma rises towards the surface and pressure falls, some of that oxygen might be released and participate in chemical reactions affecting the mantle, crust and atmosphere.

This possibility may be relevant to a period between about 2.5 billion and two billion years ago, when atmospheric oxygen increased significantly and large volcanic regions formed.

The researchers calculated that if ancient eruptions released excess oxygen equal to just 0.27 per cent of the magma’s weight, the theoretical amount could equal the oxygen currently present in Earth’s atmosphere.

However, this calculation does not prove that volcanoes supplied that oxygen. Further research is needed to determine how much oxygen natural magma can carry and how much could reach the atmosphere.

The findings may also help researchers investigate the evolution of other rocky planets and the conditions that allow habitable environments to develop.