Understanding the co-evolution Earth and life is one of the most exciting challenges in modern geoscience. This project is focused on discovering how biology may have played a role in determining when and how fast the Earth's atmosphere became oxygen-rich. Information gathered by geologists studying rocks shows that whereas oxygen produced by cyanobacteria first began to accumulate in the Earth's atmophere about 2.5 billion years ago, there was subsequently a long (> 1 billion years) delay in the rise of oxygen to the much higher levels of oxygen present in the Earth's atmosphere today. This delayed rise of oxygen in the atmosphere represents an important gap in our understanding of ancient biogeochemical cycling on Earth as well as planetary evolution in general. Mechanisms that could have stabilized the low-oxygen early Earth in the presence of oxygen producing cyanobacteria are difficult to envision, but could be revealed by investigating the biogeochemistry of today's oxygen-poor environments, especially those that have important chemical and biological similarities with environments likely to have been "normal" during the low-oxygen period in Earth's history. The project is motivated by results from initial studies of Little Salt Spring, a karst sinkhole lake with a sunlit zone poised between oxic and sulfidic (anoxic) conditions and a fast-growing pinnacle-forming cyanobacterial mat. The primary objectives are to understand what controls the balance of oxygen production and consumption in this system, especially thresholds that change the balance of oxygen production and carbon fixation. The investigator will use oxygen and sulfide microsensors (sometimes operated by science divers), a specially constructed mat manipulation chamber, recently obtained pure cultures of the main cyanobacteria in the mat, and DNA-based approaches to dissect the behavior of the ecosystem and the main cyanobacteria making up the mat.
Significant material support for the microsensor experiments will be provided free of cost via a collaboration with the Max Planck Institue for Marine Microbiology, who have a long-standing collaboration with investigator. Project funds provide for the mentoring of a Ph.D. student, an undergraduate student, and a female postdoctoral scholar, and strengthen a nascent network of collaborations among researchers in the USA and Germany. The investigator has an excellent track record of training successful female scholars at all training levels. The proposed project provides outstanding opportunities for outreach due to high public interest in underwater exploration, caves, slime, extreme microbes, and early life. Images and microbial cultures will be utilized in annual outreach and education events reaching >2000 K-12 students and parents each year as well as 150 third grade students who spend the day in hands-on science sessions.
