"In South Africa, samples from the continental slope beneath the shallower platform were thought to be deposited at water depths too deep for photosynthesis. So it was a big surprise that we found evidence of dissolved oxygen on the seafloor at these depths. This discovery suggests that oxygen was produced at the surface in large enough quantities that some oxygen survived as it was mixed to greater depths. That implies a significantly larger amount of oxygen production and accumulation in 'oxygen oases' than was previously realized."
A key contribution to this study came from Christopher Reinhard and Timothy Lyons, collaborators at the University of California, Riverside, and Simon Poulton at Newcastle University, who found that the chemistry of iron (Fe) in the same shales is also consistent with the presence of dissolved oxygen.
"It was especially satisfying to see two different geochemical methods rhenium and molybdenum abundances and Fe chemistry independently tell the same story," Kendall noted.
Evidence that the atmosphere contained at most minute amounts of oxygen came from measurements of the relative abundances of sulfur (S) isotopes. These measurements were performed by Alan Kaufman, a collaborator at the University of Maryland.
"Research like Brian's on the co-evolution of Earth's atmosphere, oceans and biosphere is not only important for unraveling key events in Earth history, it also has broad relevance to our search for life on other planets," explains Professor Ariel Anbar, director of the Astrobiology Program at ASU and Kendall's postdoctoral mentor. "One of the ways we will look for life on planets orbiting other stars is to look for oxygen in their atmospheres. So we want to know how the rise of oxygen relates to the emergence of photosynthe
|Contact: Nicole (Staab) Cassis|
Arizona State University