Catherine A. McCammon has been a leading figure in the mineral physics of Earth’s interior throughout her career and has made numerous key discoveries on the redox state of Earth and crystal chemistry at high pressures and temperatures that have been remarkably influential. Catherine is, without doubt, the foremost expert on Mössbauer spectroscopy in the field of Earth sciences. Her development in the 90s of a Mössbauer milliprobe was a game changer for understanding redox processes in the deep interior as it enabled the valence state of iron in ultrasmall samples from high-pressure experiments and natural mineral inclusions to be quantified. Catherine’s expertise in this important technique also resulted in her collaborating with many scientists from a wide range of disciplines. She has also been at the vanguard of developing synchrotron-based Mössbauer methods that allow even samples from diamond anvil cell experiments of a few hundredths of a millimeter to be analyzed.

In a discovery that profoundly changed our view of the oxidation state of Earth, Catherine showed, through high-pressure and -temperature experiments, that bridgmanite, the most abundant mineral of Earth’s lower mantle, contains large amounts of ferric iron. She also confirmed this by analyzing tiny mineral inclusions in natural diamonds that had originally crystalized as bridgmanite in the lower mantle. Catherine and colleagues showed that bridgmanite must appropriate oxygen to make ferric iron through charge disproportionation of ferrous iron, leading to the precipitation of metallic iron, which has major implications for the redox evolution of the silicate Earth. Catherine also elucidated the spin state of iron in bridgmanite at lower mantle conditions, demonstrating a high- to intermediate-spin transition near the top of the lower mantle. Taken together with her research on bridgmanite ferric iron, Catherine’s work has been instrumental in defining the physical and chemical properties of the most abundant mineral on Earth. Her innovative approaches and careful attention to important details have established her reputation as a rigorous researcher producing unique and reliable measurements at the very limit of attainable conditions. The results of her studies have been used to interpret physical properties of the deep mantle, such as seismic wave velocities and electrical conductivity, and place new constraints on the formation and evolution of Earth. Catherine has also generously served the scientific community in numerous editorial and leadership roles and is a very deserving recipient of the Harry H. Hess Medal of AGU.

— Dan Frost
University of Bayreuth
Bayreuth, Germany

I am humbled to receive this honor. Indeed, the award is as much about opportunities as it is about achievements. I am grateful to everyone who gave me those opportunities and, especially, that I had the capacity to take advantage of them. Two organizations stand out on my path to this award, and by organizations I really mean the individuals who made those organizations what they are. Bayerisches Geoinstitut, my career home for the past 33 years, provided me with opportunities to develop what was basically a niche method into a useful tool to probe Earth’s interior. Indeed, it is hard to imagine being able to achieve what I did anywhere else. I had access to extensive resources and, more importantly, enthusiastic colleagues who allowed me to thrive in the open and collaborative environment of the institute. Who wouldn’t be motivated by the stimulating atmosphere to do their best? I learned the incredible power of team work and how the skills of individuals can be combined to achieve goals that greatly exceed the sum of their parts. The other organization on my path to this award is AGU. I got to be known as a volunteer junkie, but indeed, the more I gave, the more I got back. Early on, I learned the importance of looking outside my research to the bigger picture and how to bring value to the community. I learned how to communicate to different audiences and bring respect to difficult conversations. I learned that moving outside my comfort zone led to growth beyond imagination. And I learned the value of diversity and equity and how fortunate I have been in my career. This award is dedicated to all those individuals who made those opportunities possible and gave me the capacity to take advantage of them, most importantly my family, who have supported me unconditionally throughout.— Catherine McCammon, University of Bayreuth (Retired), Bayreuth, Germany