Collaborative Research: Experimentally testing a new iron silicate model for the origin of Precambrian Iron Formations using iron stable isotope geochemistry

Earth’s largest reserves of iron ore derive from the giant iron formations, enigmatic rocks that formed in ancient seawater. These extensive iron-rich rocks signal a very different early Earth where life first emerged. However, exactly how these deposits formed is unknown and highly debated, including whether life was involved. This research project will use laboratory experiments to test which pathway(s) generate the most similar chemical fingerprints to the iron formation rocks. Thus, this research will not only help to understand how and where Earth’s largest iron ores formed but will also illuminate the chemistry and potential life of Earth’s ancient oceans—both topics that capture broad public interest. Graduate and undergraduate students will participate in the research, providing training and career advancement opportunities to the Earth science workforce. The debate about the origin of iron formations is at an impasse: iron isotopic data and other geochemical proxies such as manganese abundance seem to support primary iron oxides, but high-resolution microscopy identifies only iron silicate minerals as the original seawater mineral precipitates. However, the iron isotopic fractionation and manganese incorporation during iron silicate precipitation has never been directly measured. Recent microscale observations of the iron(II) silicate mineral greenalite has prompted new hypotheses for the origin of iron formations. This project will simulate three hypothesized formation scenarios with laboratory experiments that precipitate greenalite under different simulated ancient seawater conditions while monitoring the iron isotopic fractionation and iron-to-manganese ratios that are generated by each formation pathway. These laboratory experiments are designed to test each of three hypotheses: 1) greenalite formed as a high-pH precipitate; 2) greenalite formation was initiated by partial oxidation of Fe2+ to ferric iron (Fe3+); or 3) greenalite precipitated close to seafloor hydrothermal vents and was transported across the global oceans in plumes spreading from the seafloor. These possible pathways all have different implications for early life on Earth, the rise of oxygen in Earth’s atmosphere, and the availability of different nutrients in its ancient seawater. 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. NSF Award ID: 2515607 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Andrew Heard | Institution: Woods Hole Oceanographic Institution, WOODS HOLE, MA | Award Amount: $499,752 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2515607 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2515607.html