Faculty Mentor: Chadlin Ostrander (Geology and Geophysics, University of Utah)

The modern Earth’s atmosphere and oceans, rich in molecular oxygen (O₂), provide the chemical energy needed for the demanding metabolisms of complex life¹. Yet, this life-supporting gas was almost entirely absent for the initial half of our planet’s existence. Ushered in by the evolution of oxygenic photosynthesis, the initial rise of O₂ in surface environments around 2.5-2.2 billion years ago, dubbed “The Great Oxidation Event” (GOE), represents a dramatic turning point in Earth’s history with profound implications for our planet’s habitability. It is now recognized that instead of a simple, short-lived rise, the GOE was a protracted episode where O₂ concentrations ebbed and flowed across orders of magnitude before stabilizing at the GOE’s terminus^2,3. While significant progress has been made in understanding the timing and tempo of oxygenation near the end of the GOE^4-7, the dynamics of its early stages remain less well-known. In fact, deciphering when the GOE officially begins is still a matter of debate. To remedy this, we take a step back and analyze large compilations of geochemical data spanning 3.0-2.0 billion years ago to gain insights into the nature of oxygen rise during this interval. By analyzing the dynamics of sulfur isotopes alongside molybdenum and uranium abundances in shales, we establish a geochemical framework for defining the onset of the GOE. We plan to supplement this work by zooming in to a moment during the early stages of the GOE, where we will apply an emerging tool for tracking the oxygenation of past oceans: thallium isotope ratios.

Footnotes

[1] Catling, D. C., Glein, C. R., Zahnle, K. J., & McKay, C. P. (2005). Why O₂ is required by complex life on habitable planets and the concept of planetary” oxygenation time”. Astrobiology, 5(3), 415-438.

[2] Gumsley, A. P., Chamberlain, K. R., Bleeker, W., Söderlund, U., De Kock, M. O., Larsson, E. R., & Bekker, A. (2017). Timing and tempo of the Great Oxidation Event. Proceedings of the National Academy of Sciences, 114(8), 1811-1816.

[3] Millikin, A. E. G. et al. A new Re-Os age constraint informs the dynamics of the Great Oxidation Event. Geology 52, 857–862 (2024).

[4] Bekker, A., Holland, H. D., Wang, P. L., Rumble Iii, D., Stein, H. J., Hannah, J. L., … & Beukes, N. J. (2004). Dating the rise of atmospheric oxygen. Nature, 427(6970), 117-120.

[5] Luo, G., Ono, S., Beukes, N. J., Wang, D. T., Xie, S., & Summons, R. E. (2016). Rapid oxygenation of Earth’s atmosphere 2.33 billion years ago. Science advances, 2(5), e1600134.

[6] Uveges, B. T., Izon, G., Ono, S., Beukes, N. J., & Summons, R. E. (2023). Reconciling discrepant minor sulfur isotope records of the Great Oxidation Event. Nature Communications, 14(1), 279.

[6] Ostrander, C. M., Heard, A. W., Shu, Y., Bekker, A., Poulton, S. W., Olesen, K. P., & Nielsen, G. (2024). Onset of coupled atmosphere–ocean oxygenation 2.3 billion years ago. Nature, 1-5.