Using banded iron formations to understand habitable conditions on the early Earth
- 1Department of Earth Sciences, University of Oxford, United Kingdom (claire.nichols@earth.ox.ac.uk)
- 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- 3Department of Geoscience, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, USA
- 4Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544, USA
- 5Bruker Nano Analytics, 415 N Quay Street, Kennewick, WA 99336, USA
- 6Department of Geological Sciences, University of Colorado Boulder, UCB 399, Boulder, CO 80309, USA
- 7Origins Research Institute, Research Centre for Astronomy and Earth Sciences, MTA Centre of Excellence, 15-17 Konkoly Thege Miklos ut Budapest, 1121 Hungary
- 8Department of Lithospheric Research, University of Vienna UZA 2, Josef-Holaubek-Platz 2 A-1090 Vienna, Austria
- 9Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180, USA
- 10Ion Beam Laboratory, University at Albany State University of N.Y., 1400 Washington Avenue, Albany, NY 12222, USA
Earth is the only known inhabited world in our solar system. Criteria essential for planetary habitability include surface liquid water, a stable atmosphere, and a magnetic field. While the rock record suggests Earth has fulfilled these criteria for at least 4 billion years (Ga), both its environment and life have evolved over time. The Great Oxygenation Event (GOE), which occurred ~2.5 Ga ago, drastically altered the chemistry of the oceans and atmosphere. Decoding environmental and magnetic signals recorded in rocks prior to the GOE is essential for understanding the conditions under which life first emerged.
An ideal target for investigating surface conditions prior to the GOE are banded iron formations (BIFs), which precipitated directly from ancient oceans. However, BIFs have been significantly altered since their formation, and it is unclear whether a record of their depositional environment remains. The present day mineralogy is dominated by magnetite, but it remains to be established how this relates to the precipitates deposited on the seafloor. Additionally, in spite of magnetite's ideal magnetic properties, BIFs are avoided for paleomagnetic analysis because the timing of magnetization is uncertain. It is vital to constrain the magnetic field record leading up to the GOE because it may have influenced atmospheric hydrogen loss, contributing to rapid surface oxidation.
We present paleomagnetic field tests from the Isua Supracrustal Belt that suggest a record of Earth’s 3.7-billion-year (Ga) old (Eoarchean) magnetic field is preserved in the banded iron formation in the northernmost northeast region of the belt. Our results are supported by radiometric Pb-Pb dating of magnetite from the same banded iron formation. We show that the Pb-magnetite system has a closure temperature below 400 °C for the magnetite grain size range observed in the banded iron formation, suggesting the rocks have not been significantly heated since magnetization was acquired. This temperature range is well below the Curie temperature of magnetite (580 °C), suggesting Eoarchean magnetization has not been thermally overprinted by subsequent metamorphism. Passed paleomagnetic field tests suggest the rocks have also avoided chemical overprints. We recover an ancient magnetic field strength, supporting previous studies that argue Earth’s magnetic field has been active throughout most of its history although variations in its strength remain poorly constrained.
How to cite: Nichols, C., Weiss, B., Eyster, A., Martin, C., Maloof, A., Kelly, N., Zawaski, M., Mojzsis, S., Watson, B., and Cherniak, D.: Using banded iron formations to understand habitable conditions on the early Earth, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2404, https://doi.org/10.5194/egusphere-egu23-2404, 2023.
