'Excess oxygen' stored in deep Earth magma may help explain how Earth's atmosphere became oxygen-rich

A research team has discovered that molten rock, or magma, can hold more oxygen than its chemical makeup suggests. Their findings, published in National Science Review, indicate that oxygen makes up more than half of Earth's silicate interior. Scientists have traditionally viewed oxygen as a non-volatile component in magma, meaning it does not dissolve in the molten rock.

However, the study challenges this notion, revealing that oxygen can indeed be stored as an independent volatile component within silicate melts. To reach this conclusion, the researchers melted synthetic mid-ocean ridge basalt at various pressures and temperatures, adding platinum oxide to create an oxygen-rich environment. By measuring the elemental composition and water and carbon dioxide contents of the resulting glass, they were able to define the excess oxygen present.

The team found that the amount of excess oxygen increases with pressure, reaching more than 5 wt.% at 7 gigapascals, compared to only 0.2–0.5 wt.% at standard conditions. This indicates that magma formed in oxidized mantle regions could carry significant amounts of excess oxygen, which could be released as the magma rises and pressure decreases.

The authors propose that this release of oxygen could have contributed to major increases in atmospheric oxygen around 2.5 to 2.0 billion years ago, potentially explaining the formation of large igneous provinces during that time period.