Rethinking the Genesis of Banded Iron Formations: Simulating Partial Fe(II) Oxidation and Secondary Reactions of Iron-Silica Precipitates

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The original minerals from Earth’s primordial ocean preserve signals of the evolution of early life and ocean chemistry. To fully understand the implications of these minerals, it is necessary to recreate these phases in controlled laboratory conditions. This study focuses on the formation of iron silicates, recently identified as early minerals from marine sediments deposited during the first two billion years of Earth’s history. We will simulate the ancient ocean surface water in which a portion of iron is oxidized, the descent of the particulate products through the deep ocean, and the hypothesized respiration of the oxidized iron by microbial life in the sediments, characterizing the solid products of each step. This project will support two graduate students to lead this research and receive training in experimental geobiology. Researchers will additionally demonstrate how it is possible to recreate ancient iron precipitates in the lab and perform electron microscopy of ancient sediments with students in U-Michigan’s Earth Camp program, a summer program to expose underserved high school students to Earth and Environmental Sciences. An alum of this program who attends U-Michigan will receive a paid opportunity to assist with the proposed research, giving them valuable lab experience and a supportive laboratory community to assist in the retention of underrepresented students in the department.This project will identify likely (bio)chemical reactions that occurred in the ancient ocean and sediments, enabling to update the investigator’s model of the early iron (bio)chemical cycle. Iron-rich silicates appear to be early minerals in marine Archean (4.0 – 2.5 Ga) chemical sediments known as ‘Banded Iron Formations (BIFs)’. However, it is unknown whether reduction-oxidation (redox) processes, hypothesized to be present in the Archean ocean and often mediated by life, promoted the formation of such silicates. The proposed work will investigate what solid products are formed from plausible processes in the Archean ocean, thereby generating predictions as to which of these pathways contributed to the Archean iron cycle and how BIF minerals, particularly iron silicates, may reflect ancient (bio)chemical reactions. Specifically, researcher will answer the questions: 1) What are the initial solid products of partial Fe(II) oxidation under hypothesized Archean ocean conditions? 2) How are the initial solid products of partial iron oxidation chemically modified under Archean oceanic water column conditions? 3) How does microbial respiration of Fe(II,III)-silica products transform their chemistry and mineralogy? The experiments will address these questions by replicating Archean water column environments with trace levels of O2, then exposing these solids to anoxic water column conditions to simulate exposure during particle descent, followed by simulating early diagenesis by feeding these precipitates to an iron-reducing bacterial strain. This process-based, mechanistic approach will determine which plausible redox reactions in the Archean ocean produce iron silicates or other minerals found in BIFs, yielding insights into the interplay between life and geochemistry in the Archean Eon.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.