Researchers supported in part by the Exobiology Program have provided new information about the oxygenation history of the Earth’s oceans during the mid-Proterozoic using uranium (U) isotope data. The team collected isotopic data from marine rocks that span the mid-Proterozoic (some 1.8 to 0.8 billion years ago). The data was used as a proxy to constrain the amount of global marine euxinia, which refers to environments low in oxygen and high in hydrogen sulfide.

Understanding the extent of euxinia in ancient marine environments is important because sulfide limits the solubility of trace metals that are essential for living organisms. Sulfide toxicity could have been a major barrier to evolution in mid-Proterozoic oceans. However, the results suggests that euxinia in the mid-Proterozoic was less widespread than previously thought, affecting only about 7% of the seafloor.

The study, “Uranium isotope evidence for limited euxinia in mid-Proterozoic oceans,” was published in the journal Earth and Planetary Science Letters. The work was supported by NASA Astrobiology through the Exobiology Program. This newly-revealed science is also a critical part of NASA’s work to understand the Universe, advance human exploration, and inspire the next generation. As NASA’s Artemis program moves forward with human exploration of the Moon, the search for life on other worlds remains a top priority for the agency.