TEXAS A & M RESEARCH FOUNDATION

This project's objective is to identify the source of oxidized iron minerals in the 3.26-billion-year-old Manzimnyama Jaspillite Member of South Africa, one of the oldest well-preserved examples of a class of rocks called banded iron formations. Banded iron formations provide a record of iron oxidation occurring in the Earth?s oceans from >3.7- to 1.8-billion-years-ago. One of the first hypotheses explaining the origins of these rocks suggested that oxygen produced by photosynthetic bacteria growing in shallow water reacted with dissolved iron supplied from the deep ocean, producing oxidized iron minerals which settled to the sea floor. Banded iron formations were therefore thought to provide evidence for the very early evolution of oxygen-producing photosynthetic bacteria. However, later hypotheses have provided alternative explanations for early iron oxidation. In some circumstances, exposure to ultraviolet light can rapidly oxidize dissolved iron, so it is possible that some early banded iron formations may have been formed without the action of living organisms. It is now also known that some photosynthetic bacteria can oxidize iron directly without producing oxygen. Since non-oxygen-producing photosynthesis evolved before oxygen-producing photosynthesis, it is possible that early banded iron formations formed in this way. At present, there is no known way to determine which hypothesis is correct for any particular banded iron formation. Successfully testing these hypotheses will provide important new evidence about the evolution of photosynthesis and the early biosphere. Our approach exploits characteristics of two naturally occurring metals, manganese and cerium, both of which oxidize in the presence of oxygen. Critically, neither should be oxidized as rapidly as iron by ultraviolet light or at all by iron-oxidizing photosynthetic bacteria. Our predictions are that 1. banded iron formations formed in the presence of oxygen would contain oxidized manganese and cerium; 2. banded iron formations formed primarily from ultraviolet promoted iron oxidation would contain some oxidized manganese and cerium but much less than those formed in the presence of oxygen; 3. and that banded iron formations formed by iron-oxidizing (non-oxygen-producing) photosynthetic bacteria would not contain any oxidized manganese and cerium. We will test this hypothesis by conducting metal oxidation experiments with ultraviolet light, oxygen-producing photosynthetic bacteria, and iron-oxidizing photosynthetic bacteria to measure the relative oxidation rates of iron, manganese, and cerium under these three conditions. We will simultaneously test for variations in relative iron, manganese, and cerium sedimentation rates in the Manzimnyama Jaspillite Member and the 3.42-billion-year-old Buck Reef Chert, an iron-rich unit showing no evidence for iron oxidation. Geological results will be compared with experimental results to infer the major process responsible for iron oxidation during deposition of a 3.26-billion-year-old banded iron formation. Broader Impacts: All research will be conducted by a graduate student supervised by the PI and co-PI. In addition, experimental work will be aided by an undergraduate student, potentially for an undergraduate honors thesis. Results and specific experiments will be incorporated into a graduate level geobiology course taught by the PI and an undergraduate course in astrobiology and early life to be developed by the PI and co-PI. The undergraduate course will be organized so as to take advantage of long-distance learning web technology to serve undergraduates throughout the Texas A&M University System, including campuses with high populations of underrepresented minorities.

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