I studied physics and mathematics at The Evergreen State College and astronomy at The University of Washington, but the bulk of my scientific career has involved the study of the early Earth. This (admittedly somewhat indirect) path was enabled by the unique interdisciplinary graduate program in Astrobiology at UW from which I received a graduate certificate. The Astrobiology program enabled training in the full breadth of planetary sciences coursework (in the Astronomy, Earth and Space Sciences (ESS), and Atmospheric Sciences departments) as well courses in Oceanography and Microbiology not typically taken by astronomers. It was via the interdisciplinary “Astrobiology Research Rotation” that I first expanded my skill set from modelling and learned to run isotopic measurements on a mass spectrometer, in the lab of Roger Buick and Eric Steig. I was lucky to obtain a (now defunct) NASA Graduate Student Research Fellowship with David Catling (ESS) and Kevin Zahnle (NASA-Ames) as thesis advisors, despite the fact that David resided outside my home department, and Kevin was employed by a NASA center. I chose an astronomy department for my graduate home because my ultimate inspiration stems from the inevitable day when we detect spectrally-resolved light from the atmospheres of Earth-like terrestrial exoplanets, and can determine if they contain biosignatures like the oxygen-methane couple in Earth’s modern atmosphere. Crucially, the quantitative information we will someday be able to extract about surface conditions and atmospheric disequilibrium caused by a planetary biosphere is only as good as our underlying models of atmospheric chemistry, which has motivated my studies into atmospheric evolution on Earth.
As a result of this training, I have been privileged to be able to study atmospheric evolution from a number of interdisciplinary angles. My doctoral dissertation, titled “Quantitative biogeochemical models of the rise in atmospheric oxygen”, involved reviewing Earth’s rock record (Catling and Claire, 2005), using global box models of biogeochemical cycles of oxygen, carbon, hydrogen, and iron (Claire et al., 2006; Catling et al., 2007), and a detailed study of the atmospheric photochemistry of oxygen, methane, and sulfur before and after the Great Oxidation Event (Zahnle et al., 2006). I have continued to expand all three of these themes in my subsequent career, using both a “top-down” approach utilizing numerical modelling and a “bottom-up” approach of using geochemical measurements to constrain paleo-atmospheric composition
Immediately following my PhD, I was able to branch out into Martian research when the NASA Astrobiology Institute (NAI) Directors Discretionary Fund (DDF), funded a 6-month project titled “Volcanic SO2, atmospheric chemistry, and climate on early Mars.” In the week before the project kickoff meeting, NASA’s Phoenix Lander published results that ranked among the most unexpected planetary science results of the decade – namely that perchlorate was the dominant soluble salt in Martian soil. I shifted my attention to this exciting new topic, while a fellow postdoc on the grant finished the original project (Tian et al., 2010). In search of a mechanism to produce the unexpected Martian perchlorate, I adapted the 1-D photochemical model to include higher-order chlorine species, resulting in the first predictive model of atmospheric perchlorate in the Mars-analogue Atacama desert, Chile (Catling et al., 2010) (David Catling was first author as he was a formal member of the Phoenix science team, but the work was mostly my own). This work has thus far led to an additional publication on perchlorate brine chemistry (Marion et al., 2010) as well as two additional grants, a 2012 NASA NAI DDF award “Perchlorate, water, and life” and an American Philosophical Society Lewis and Clark Fellowship for fieldwork in Chile. I moved to a faculty position at the University of East Anglia soon after receiving these grants, and was forced to re-direct most of the 2012 DDF award to Meg Smith, then a graduate student at the University of Washington, who published the first work on atmospheric perchlorate formation on Mars (Smith et al., 2014). I lacked the support to complete sample analyses while at UEA, but with the opening of the new Geobiology Laboratory at the University of St Andrews, additional geochemical work on the Atacama samples is nearing completion. In the meantime I’ve continued to work on perchlorate-related science, making the first measurement of perchlorate in martian meteorite EETA79001 (Kounaves et al., 2014), and have been awarded 5g of the Tissint meteorite from the British Museum in London. I’ve recently returned from a field expedition to the Tissint Mars meteorite fall site in Morocco, with exciting new samples.
In addition to the two DDF awards, the NAI was kind enough to further support me with a 2-year postdoctoral fellowship at the Virtual Planetary Laboratory. In this fellowship, working alongside Vikki Meadows and Jim Kasting, I compiled and standardized measurements of the evolution of Earth’s solar flux (Claire et al., 2012). In addition, I continued to actively develop the photochemical model and collaborated on the photochemical details of several projects related to astronomical detection of biosignatures on exoplanets (Domagal-Goldman et al., 2011; Domagal-Goldman et al., 2014; Misra et al., 2014). My first PhD student Andrew Rushby is also interested in planetary habitability, and has completed a very nice dissertation on the evolution of Earth’s carbon cycle and a comprehensive re-evaluation of the circumstellar habitable zone (Rushby et al., 2013). I remain fascinated with global biogeochemical cycles and have published on the biogeochemical cycling and atmospheric evolution of nitrogen (Goldblatt et al., 2009; Izon et al., 2015), the critical role of hydrogen escape on the evolution of atmospheric oxygen (Zahnle et al., 2013), and even became involved in microbiological experiments testing a key prediction regarding the anaerobic oxidation of methane stemming from my thesis work (Beal et al., 2011). Most recently, I have become increasingly focused on interpreting Earth’s rich geological record (Zerkle et al., 2012; Farquhar et al., 2013; Kurzweil et al., 2013; Claire et al., 2014; Izon et al., 2015), developing an interest in modeling the mass-independent fractionation of sulfur and oxygen isotopes to provide quantitative constraints on atmospheric chemistry.
That’s probably more than you wanted to know about me. Thanks for reading. If you are interested in more details on any of these papers, check out the publication page