Oxygen is one of the fundamental elements necessary to sustain life. Traditionally, the presence of oxygen in a planetary atmosphere has been linked to biological processes, specifically photosynthesis. However, a newly discovered dark oxygen is challenging the belief that the element could only be created from sunlight – which could have wild implications in astrobiology.
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What is Dark Oxygen?
The oxygen that sustains complex life forms on Earth is diatomic molecular oxygen (O₂) created through sunlight via the photosynthesis process. This strong association has led scientists to believe that oxygen in planetary atmospheres is a reliable indicator of photosynthetic life. However, "dark oxygen," a term coined to describe a newly discovered form of oxygen, appears to be a new type that does not rely on sunlight or photosynthesis for its creation. 1, 2
How was it Discovered?
The discovery of dark oxygen production at the bottom of the sea was made through a series of experiments conducted in the Clarion–Clipperton Zone (CCZ) of the Pacific Ocean. Researchers deployed benthic chamber landers - autonomous enclosures that isolate sections of the seafloor to measure oxygen fluxes. These experiments were performed in areas densely covered with polymetallic nodules. Instead of the anticipated drop in oxygen levels from biological respiration and oxidation, scientists observed an increase in oxygen concentration—more than three times the background levels—over a 47-hour period.
This dark oxygen production phenomenon was confirmed using oxygen optodes and independently verified through the Winkler titration method to rule out equipment malfunctions. 1
Researchers further conducted additional ex-situ incubations of sediment cores and nodules, including tests involving poisons like mercury chloride to eliminate biological activity as a potential cause. The results indicated that the presence of polymetallic nodules played an important role in oxygen generation. Additionally, the electrical measurements on the nodules showed voltage potentials of up to 0.95V, suggesting a possible electrochemical process akin to seawater electrolysis. Researchers hypothesized that energy differences between metal ions within the nodules could drive an electrochemical reaction, liberating oxygen in the absence of sunlight. This discovery challenges the conventional understanding of deep-sea oxygen dynamics and suggests that deep-sea electrochemical processes may play an unrecognized role in marine ecosystems. 1
Implications for Astrobiology
The discovery of dark oxygen has significant implications for astrobiology as it suggests that oxygen production, and potentially life, can exist in environmental conditions that were previously considered inhospitable. This is particularly relevant to the search for life on other planets and moons.
One of the key implications is the potential for dark oxygen to exist on icy moons such as Europa and Enceladus. These moons possess subsurface oceans that may contain the necessary ingredients for life, and the discovery of dark oxygen suggests a potential mechanism for sustaining oxygenated habitats in these environments. 3
Moreover, dark oxygen could also act as a biochemical building block for unknown forms of alien life. Its unique properties, such as potential stability in extreme conditions, could allow it to sustain life under extreme pressure and low-temperature conditions.
Advancing Our Understanding of Space Chemistry
Oxygen detection on an exoplanet has often been considered a potential biosignature. However, dark oxygen complicates this assumption by showing that oxygen might exist independently of biological processes.
Dark Oxygen demonstrates that oxygen can be naturally produced through abiotic processes, meaning that the detection of oxygen in an exoplanet's atmosphere does not automatically indicate the presence of life, which calls for a more nuanced approach to assessing their habitability. 2, 4 ,5
Moreover, dark oxygen may have links to abiogenesis, the origin of life from non-living matter. If oxygen can be produced in the absence of life, it suggests that the early Earth may have had pockets of oxygenated environments even before the evolution of photosynthetic organisms. These environments could have been responsible for the emergence of the first life forms. 2, 4
This discovery is an indication of the diversity and complexity of chemistry in the universe, as it demonstrates that there are still many unknown chemical processes occurring in extreme environments, both on Earth and potentially on other celestial bodies.
What Now?
Detecting and characterizing dark oxygen beyond Earth will require refined tools and novel methodologies. For instance, current spectroscopic techniques used to analyze planetary atmospheres may need refinement to distinguish between spectral signatures of conventional oxygen and dark oxygen exoplanet atmospheres.
Space agencies could design missions to search for dark oxygen in the atmospheres of exoplanets or within our solar system. The James Webb Space Telescope (JWST) and future space observatories like the Extremely Large Telescope (ELT) may be instrumental in detecting its presence in distant star systems as well.
Another avenue for research can be the development of experimental setups on Earth to simulate the extreme conditions where dark oxygen is thought to exist. Examining its interactions with other elements and molecules in simulated space environments could offer further insights into its stability and possible role in extraterrestrial chemistry.
Broader Implications for the Future of Space Exploration
Dark oxygen has the potential to impact the search for life beyond Earth by widening the range of habitable conditions. Moreover, dark oxygen could have potential uses in future human space exploration. It could potentially be harnessed for energy production or life-support systems on long-duration missions. If dark oxygen can be produced on other planets or moons, it could for instance provide a sustainable source of breathable air for astronauts. However, the potential environmental impacts of exploiting dark oxygen sources, such as deep-sea mining, must also be carefully considered. Deep-sea mining, which is used to extract valuable metals from polymetallic nodules, has been associated with biodiversity loss and habitat destruction.
References
- Sweetman, A. K., Smith, A. J., de Jonge, D. S., Hahn, T., Schroedl, P., Silverstein, M., ... & Marlow, J. J. (2024). Evidence of dark oxygen production at the abyssal seafloor. Nature Geoscience. https://doi.org/10.1038/s41561-024-01480-8
- Lingam, M., Balbi, A., & Tiwari, M. (2024). Dwellers in the Deep: Biological Consequences of Dark Oxygen. arXiv preprint arXiv. https://doi.org/10.48550/arXiv.2408.06841
- Evan Gough (2024) Dark Oxygen Could Change Our Understanding of Habitability. Universe Today. https://www.universetoday.com/168357/dark-oxygen-could-change-our-understanding-of-habitability/
- Ruff, S. E., Humez, P., de Angelis, I. H., Diao, M., Nightingale, M., Cho, S., ... & Strous, M. (2023). Hydrogen and dark oxygen drive microbial productivity in diverse groundwater ecosystems. Nature Communications. https://doi.org/10.1038/s41467-023-38523-4
- Joe Hernandez, & Regina G. Barber (2024). Scientists may have discovered 'dark oxygen' being created without photosynthesis. NPR. https://www.npr.org/2024/07/24/nx-s1-5049587/scientists-dark-oxygen-without-photosynthesis
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