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Oxygen Production from Volcanic Sulfur Dioxide Photochemistry: A Possible Trigger for the Earth's Great Oxidation Event

Posted: 2023-08-18

The provenance of oxygen (O2) has been linked to the early Earth's atmospheric and biological evolution. A permanent rise to appreciable concentrations of O2 in the atmosphere, known as the "Great Oxidation Event (GOE)", was estimated to have occurred at around 2.4 billion years ago. However, the cause of the GOE still remains unclear.

Besides the biogenic processes leading to O2 production, the widely accepted abiotic O2 production is through photolysis of carbon dioxide (CO2) and water molecule (HO2).

Now, a research group led by Prof. YUAN Kaijun and YANG Xueming from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has reported oxygen production from vacuum ultraviolet photodissociation of sulfur dioxide (SO2) using the Dalian Coherent Light Source.

Their findings were published in Chemical Science on Aug. 1. The article was chosen as a Hot Article.

Dalian Coherent Light Source revealing vacuum ultraviolet photodissociation of sulfur dioxide as an important prebiotic-O2 source (Image by YUAN Kaijun)

"Our experimental results revealed a direct dissociation channel yielding S(1D) + O2 products from vacuum ultraviolet (VUV) photodissociation of SO2 in the wavelength range between 120 and 160 nm," said Prof. YUAN.

Geological evidences have identified the strong activity of SO2 photochemistry during the Earth's late Archaean eon, which linked to the origin of the sulfur mass independent fractionation in ancient rocks. But its role in the formation of molecular oxygen is ignored.

The quantitative determination demonstrated that O2 production was an important channel from SO2 VUV photodissociation, with a branching ratio of around 30% at the H Lyman-a wavelength (121.6 nm).

The relatively large amounts of SO2 emitted from volcanic eruptions in the Earth's late Archaean eon imply that VUV photodissociation of SO2 could have provided a crucial additional source term in the O2 budget in Earth's primitive atmosphere. Therefore, this event may lead to transient O2 accumulation and could be one possible cause of the GOE.

This research was supported by the Chemical Dynamics Research Center, and the National Natural Science Foundation of China.