How volcanic eruptions contributed to Earth’s oxygen-rich atmosphere

Scientists have discovered that sulfur dioxide from ancient volcanoes played a key role in the rise of atmospheric oxygen levels around 2.4 billion years ago.

Around 2.4 billion years ago, Earth experienced a significant surge in atmospheric oxygen levels during the great oxidation event. The cause of this event has long puzzled researchers. The breakdown of carbon dioxide by photosynthetic organisms has been cited as a likely contributor, but it could not explain the sudden and dramatic increase in oxygen.

A new source of oxygen: sulfur dioxide

Researchers from China, led by Kaijun Yuan, have made a ground-breaking discovery: a portion of this oxygen likely originated from the breakdown of volcanic sulfur dioxide. Sulfur dioxide (SO2) is a non-inflammable colorless gas that is produced by volcanic eruptions and fossil fuel combustion. SO2 is usually oxidized by ozone and hydrogen peroxide to form sulfur trioxide, a secondary pollutant that is extremely soluble in water. Droplets of sulfuric acid (acid rain) are formed when sulfur oxides are present in the atmosphere.

How volcanic eruptions contributed to Earth’s oxygen-rich atmosphere
How volcanic eruptions contributed to Earth’s oxygen-rich atmosphere

Volcanic eruptions that took place before the great oxidation event, during a period known as the Archean eon, produced large amounts of gaseous sulfur dioxide. While the possibility of this breakdown to produce oxygen has been studied before, its importance in relation to our current atmosphere was unclear.

A laser experiment to recreate ancient conditions

Kaijun Yuan and his team conducted extensive experiments using the intense vacuum ultraviolet free electron laser at the Dalian Coherent Light Source in China. This unique tool was instrumental in helping researchers precisely understand how molecules dissociated under different wavelengths and pressures.

The scientists’ experiments showed that the dissociation of sulfur dioxide into oxygen and a sulfur atom was possible in the atmospheric conditions of that time. The team estimates that around 4.3% of our current atmospheric oxygen came from volcanic sulfur dioxide.

Implications for Earth and beyond

These findings may also have implications for our understanding of how sulfur dioxide behaves in the atmospheres of other planets and moons in our solar system. For example, sulfur dioxide is present in large quantities on Venus and Io, a moon of Jupiter. Studying how this gas interacts with other atmospheric components could shed light on the evolution and habitability of these celestial bodies.

The study also highlights the importance of using advanced tools and techniques to investigate the complex and dynamic history of our planet’s atmosphere. By recreating prehistoric conditions and reactions, scientists can gain new insights into how Earth became a hospitable place for life.

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