Molecular oxygen (O2) is essential for respiration on today’s Earth, but the early atmosphere is almost devoid of oxygen until the great oxidation event. However, early life acquired a defensive ability against reactive oxygen species (ROS) beneath the anoxic Archean atmosphere even before the evolution of biologic O2, which is associated with abiotic oxidants. It is traditionally believed that the Earth’s initial oxygen derived from water splitting, e.g., the atmospheric photochemistry H2O2. But is that really the case?
Recently, a research team led by Prof. HE hongping from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences discovered that ROS production at mineral-water interfaces derives oxygen from minerals. This finding has overturned the traditional view that oxygen generally derives from water splitting.
The study was published in Proceedings of the National Academy of Sciences on Mar. 20.
To identify the origin of the Earth’s initial oxygen, the researchers confirmed the appearance of reactive oxygen-containing sites (≡SiO？, ≡SiOO？) on the abraded quartz and the ROS production during contact of the abraded quartz with water. They employed 18O-labeled water (H218O) as a tracer to track the oxygen source of ROS generated at mineral-water interface. Their isotope-labeling experiments show that the hydroxylation of the peroxy radical (≡SiOO？) is the predominant pathway for H2O2 generation, followed by the decomposition of H2O2 into O2 and H2O, while only a small portion of oxygen in ROS derives from water. This heterogeneous ROS production chemistry allows the transfer of oxygen atoms between water and rocks and alters their isotopic compositions. More importantly, this study suggests that the evolution from mafic crust to felsic crust is critical for the habitability of the early earth and drove the multilayer co-evolution of lithosphere, hydrosphere, atmosphere, and biosphere.
The oxygen transfer pathways at the quartz-water interfaces are unexpected and novel as isotopic exchange between water and mineral surface. “With proper geologic proxies that can record isotope compositions of O2, ozone and radical derived species (e.g., sulfate), this finding provides a novel prototype to examine various early Earth's H2O2 production models (e.g., photochemical, mechanochemical).” said Prof. Mark H. Thiemens and LIN Mang, collaborators in this work.
This reaction may be initiated by mechanical forces in various geodynamic processes, which deform minerals to produce surface radicals for releasing oxygen by interaction with water. Such rocky oxidants created opportunities for life and drove its early evolution. “This ubiquitous abiotic oxygen source can be important for the detection of extraterrestrial life, as highly energetic aerobic respiration and even the evolution of complex multicellular life are possible.” said Prof. HE.
Materials provided by Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.
Hongping He*，Xiao Wu，Jianxi Zhu，Mang Lin，Ying Lv，Haiyang Xian，Yiping Yang，Xiaoju Lin，Shan Li，Yiliang Li，H. Henry Teng，Mark H. Thiemens*, 2023. A mineral based origin of Earth's initial hydrogen peroxide and molecular oxygen. Proceedings of the National Academy of Sciences of the United States of America. Article DOI: 10.1073/pnas.2221984120
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences