Magma Can Hold Far More Oxygen Than Thought, Lab Tests Show

Molten rock deep inside Earth can store much more oxygen than scientists have long assumed, according to a study published in National Science Review and described by ScienceDaily on Oct. 28. The researchers say the finding points to a possible hidden link between the planet's interior, volcanic eruptions and the oxygen-rich atmosphere that developed billions of years ago.

The work combined high-pressure laboratory experiments with computer simulations. It was led by Yanhao Lin and Ho-kwang Mao of the Center for High Pressure Science and Technology Advanced Research, with Haiyang Niu of Northwestern Polytechnical University and Wim van Westrenen of Vrije Universiteit Amsterdam.

The central numbers behind the finding

• 7 gigapascals: the highest pressure in the experiments, which ScienceDaily says is roughly 69,000 times the atmospheric pressure at Earth's surface.
• 1200 to 1800 °C: the temperature range in which the team heated a synthetic version of mid-ocean ridge basalt, a volcanic rock formed where tectonic plates pull apart under the oceans.
• More than 5%: the share of the sample's weight made up of excess oxygen at 7 gigapascals, in glass made by rapidly cooling the melt.
• 0.2% to 0.5%: the excess oxygen found at similar pressures and temperatures when the team did not add platinum oxide, which was used to create an oxygen-rich environment.
• Almost none: the excess oxygen in the glass at normal atmospheric pressure.

What scientists used to assume about magma

Oxygen is one of the most abundant elements in Earth's interior, making up more than half of the atoms in its silicate material, the silicon- and oxygen-rich minerals and melts that form much of the mantle and crust. Even so, the standard view held that magma contains only a fixed amount of oxygen, set by the amounts and electrical charge states of other elements such as silicon, magnesium and iron.

Water and carbon dioxide are treated differently. They dissolve in magma and escape as gases when pressure drops, which helps drive volcanic activity. Oxygen has generally not been viewed as a similar substance that melt can absorb and release independently of its ordinary chemical makeup. Whether it could was largely unexplored, the researchers say.

How the team measured "excess oxygen"

After the experiments, the researchers analyzed the composition of the glass and measured its water and carbon dioxide. By working out how much oxygen was needed to balance the other elements, plus the oxygen already tied up in water and carbon dioxide, they estimated how much was left over. They called that remainder excess oxygen.

To check whether the oxygen was truly built into the material rather than trapped in tiny bubbles, the team used Raman spectroscopy, a technique that identifies substances by how they interact with light. It found no detectable signature of oxygen gas, which indicates the oxygen had become part of the glass structure.

The researchers add that their numbers may understate the real capacity. Some oxygen could have escaped as the samples cooled, so the original melts may have held even more.

What the computer simulations added

Niu led simulations that used deep neural network models to mimic how atoms interact, with accuracy approaching that of ab initio calculations, which rely on the fundamental principles of quantum mechanics. In those models, extra oxygen dissolved into molten material until the amount entering and leaving the melt was balanced.

The simulations used a simplified system containing only magnesium, silicon and oxygen. Even so, they reproduced the same overall pattern seen in the laboratory.

Why it matters: oxygen, volcanoes and the early atmosphere

The practical stakes here are about understanding Earth's history rather than anything that changes daily life. If magma can carry extra oxygen, the researchers suggest, ancient volcanic eruptions could have helped release oxygen from the planet's interior and contributed to the transformation of the atmosphere billions of years ago. ScienceDaily's summary says the findings could also inform how scientists think about life on other planets.

The result comes from experiments on a synthetic rock under controlled conditions, and the simulations used a simplified system. How much oxygen real magma stores, and how much of it reached the air, was not established by this study.

Around Prague, based on reporting by ScienceDaily