Fully Funded PhD positions in the evolution of atmospheric oxygen

Interested in the evolution of Earth’s atmosphere?

Three cutting-edge PhD projects constraining the rise and fall of atmospheric oxygen starting soon at St Andrews

Led by Dr Mark Claire

Atmospheric oxygen is fundamental to life as we know it, but its concentration has changed dramatically over Earth’s 4.5 billion year history. An amazing qualitative story has emerged, in which Earth’s atmosphere was devoid of free oxygen for the first 2 billion years of planetary history, with two significant increases in concentration at ~2.4 and ~0.55 billion years ago. Both oxygenation events were accompanied by extreme climatic effects – the “snowball earth” episodes – and paved the way for massive reorganization of biogeochemical cycles such as the Cambrian radiation of macroscopic life. Despite these profound influences on the Earth system, we currently lack fundamental quantitative constraints on Earth’s atmospheric evolution.

The three available projects span a wide range of disciplinary backgrounds:

Detailed information about each project can be found on the links below. A downloadable flyer briefly describing all three is here.

Experimental constraints on oxygen-free atmospheres
Geochemical measurements of triple oxygen isotopes across key intervals in Earth History
Numerical modelling of oxygen isotopes in the atmosphere over key intervals in Earth History

Additional background information about all three projects:

The evolution of atmospheric oxygen encompasses some of the great questions in Earth systems science [1], including: the causes (and consequences) of the most dramatic biogeochemical event in Earth’s history, the Great Oxidation Event (GOE) approximately 2.4 billion years ago (Ga) [2]; why it took more than a billion years after the GOE for the second great rise in oxygen, coincident with (and allowing for) the radiation of macroscopic life and motile animals [3]; and even why Earth’s earliest atmosphere was devoid of O2 [4]. Despite recent advances in understanding this general pattern of atmospheric evolution [1, 5], detailed compositional constraints remain elusive (Figure 1).

Figure 1 - A cartoon showing atmospheric oxygen proxies and their uncertainties. From Kump, Nature (2008)

Figure 1 – A cartoon showing atmospheric oxygen proxies and their uncertainties. From Kump, Nature (2008)

This 5 year ~£1.3M project funded by the European Research Council aims to establish quantitative constraints on the evolution of atmospheric composition through more than 3 billion years of Earth history by coupling cutting-edge experiments with comprehensive atmospheric models underpinned by two key isotopic datasets. Theme 1 of the research will integrate data from novel photochemical experiments on the mass-independent fractionation of sulfur isotopes (MIF-S) with my numerical model for atmospheric composition [5-7]. In Theme 2, my student and I will extend the interpretation of MIF-oxygen into deep time, using novel analytical advances on samples from key geological archives and state-of-the-art modeling to constrain oxygen concentrations in the aftermath of the GOE. Theme 3 spans the MIF-S and MIF-O work and will focus on increasing the predictability of the atmospheric models by identifying, quantifying and reducing the largest sources of error. Combined, the careful merging of novel experiments, high-throughput data generation, and numerical modelling should provide a step-change in our ability to quantitatively constrain the evolution of atmospheric chemistry over Earth history.

The Primary Question: How can we extract fundamental quantitative constraints on the evolution of atmospheric composition from mass-independent fractionation of S and O in the rock record?

Figure 2 – A compilation of sulfur and oxygen MIF data, from Bao (2014) and Claire et al. (2014). Large sulfur MIF (Δ33S – blue diamonds) appears in the rock record between 4 and 2.4 billion years ago (Ga) whilst large oxygen MIF (∆17O – red circles) is absent; the inverse occurs between 2.4 Ga and the present. These data constrain the broad evolution of atmospheric oxygen from trace to major concentrations but there is a wealth of yet untapped information in these data sets.

Figure 2 – A compilation of sulfur and oxygen MIF data, from Bao (2014) and Claire et al. (2014). Large sulfur MIF (Δ33S – blue diamonds) appears in the rock record between 4 and 2.4 billion years ago (Ga) whilst large oxygen MIF (∆17O – red circles) is absent; the inverse occurs between 2.4 Ga and the present. These data constrain the broad evolution of atmospheric oxygen from trace to major concentrations but there is a wealth of yet untapped information in these data sets.

The record of mass-independent fractionation of S and O seen in Figure 2 are rich in information to place quantitative constraints on the temporal evolution of such important atmospheric gases as O2, O3, CH4, and CO2.

The overall goal is to develop quantitative models of atmospheric composition beyond the presence or absence of O2. The fundamental challenge is to overcome the shortcomings of limited data, expensive analytical methodologies, over-extrapolation of experimental results and uncertain modelling that, combined, hinder obtaining insights into MIF-O and -S trends through Earth history. Solutions involve innovative experiments to illuminate MIF-S formation and a novel analytical methodology enabling a rapid obtaining of MIF-O data. Coupled with state-of-the-art numerical models and a project-wide goal to quantify and reduce uncertainty, my team will determine, from quantitative numerical constraints, the evolution of oxygen and other gases in Earth’s atmosphere unprecedented accuracy including quantified errors. These advances will enable us to test cutting-edge hypotheses ranging from biological influence on the composition of Earth’s atmosphere prior to the Great Oxidation Event to massive CO2 greenhouses in the aftermath of the Neoproterozoic “Snowball Earth.”

I very much look forward to training the next generation of Earth systems scientists. I hope to foster a tight network of scientists ranging from undergrads to postdoctoral scholars working together on collaborative projects to answer these questions, while provide skills and opportunities needed for twenty first century careers. Please get in touch if you have any questions or want to be a part of it. (mc229 at st-andrews.ac.uk)

REFERENCES:
[1] Lyons, T. W., Reinhard, C. T. & Planavsky, N. J. 2014, Nature, 506, 307-315
[2] Bekker, A., Holland, H. D., Wang, P. L., et al. 2004, Nature, 427, 117-120
[3] Knoll, A. H. & Carroll, S. B. 1999, Science, 284, 2129-2137
[4] Catling, D. C. & Claire, M. W. 2005, EPSL, 237, 1-20
[5] Claire, M. W., Kasting, J. F., Domagal-Goldman, S. D., et al. 2014, CGA, 141, 365-380
[6] Zerkle, A. L., Claire, M., Domagal-Goldman, S. D., et al. 2012, NatGeosci, 5, 359-363
[7] Kurzweil, F., Claire, M., Thomazo, C., et al. 2013, EPSL, 366, 17-26

(Please contact Mark if you have trouble gaining access to any of these references)

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