John J. Braswell
Years participated in RESESS:
Understanding past conditions of early Earth using trace metals in sulfide minerals
Academic Affiliation: Senior, University of Michigan, Earth Science
Science Research Mentor: Stephen Mojzsis – University of Colorado at Boulder
Writing and Communication Mentor:Beth Bartel – UNAVCO
It is widely believed that drastic changes in Earth’s biosphere led to the great oxidation event (GOE), a sudden increase in atmospheric oxygen approximately 2.5-2.4 Ga. Nickel is an essential nutrient for methanogens, and there was a decrease in nickel Production during this time due to Earth's cooling. The emergence of cyanobacteria and the declining population of methanogens resulted. Cyanobacteria are photosynthetic bacteria that supplied an appreciable amount of oxygen to the atmosphere by first oxygenating the ocean surface. This created an iron oxide which settled to the bottom of the ocean floor as sediments in layered deposits called banded-iron formations (BIF). Once iron was nearly depleted, the release of oxygen from the oceans filled the atmosphere. BIF store geochemistry signatures from early Earth that contain sulfide minerals with various amounts of trace metals in each sulfide mineral. By studying the abundance of trace metals (Ni, Zn, Cu, Co, Mo) before and after GOE, we can better understand the catalytic processes that were influential. Through use of an electron microprobe, new lines of evidence can be obtained to support the theory of the rise of atmospheric oxygen. Analysis of Ni/Fe ratio coincides with the nickel famine theory. During the GOE, there was a decrease in Co/Fe ratios. The other trace metals noted above are under further investigation.