Roberta Rudnick was awarded the 2017 Harry H. Hess Medal at the AGU Fall Meeting Honors Ceremony, held on 13 December 2017 in New Orleans, La. The medal is for “outstanding achievements in research on the constitution and evolution of the Earth and other planets.”  

Earth’s crust is important to us because we happen to live on it. It also contains more than half of Earth’s internal heat production, as well as most of its potassium and phosphorus. Its formation has left the residual mantle in a dramatically different state. Thus, knowing its composition is critical to any understanding of how Earth’s interior works. Roberta Rudnick is the world’s leading authority on the composition of the continental crust and lithosphere. Toward this end, she integrated geophysical properties of the crust with a comprehensive array of geochemical data to elucidate the role of the lower crust, which is inaccessible to direct observation. Today, if one is looking for the best estimate of the average continental crust or of its upper or lower portions, the ­go-to papers are those of Roberta Rudnick and her coworkers David Fountain and Shan Gao. The continental crust is welded to a much more massive subcontinental lithosphere. To elucidate the origin and evolution of this lithosphere, Roberta has conducted definitive studies on lithospheric peridotite and eclogite xenoliths, concentrating on trace element and isotope systems.

During the past several years, she has also become a leader in using one of the new, often called unconventional tracers, namely, lithium isotopes, to study ­near-­surface continental processes such as weathering and intracrustal fluid flow, as well as recycling of ­near-­surface continental material into the mantle. With her graduate student ­Fang-­Zhen Teng, she demonstrated unequivocally, through detailed field and analytical work on magmatic aureoles, that reactive transport causes kinetic isotope fractionation. This work has opened up a new area of research on using kinetic isotope fractionation to constrain the timescales of diffusive and advective geochemical processes.

Most recently, together with her postdoc Richard Gaschnig and student Ming Tang, she has tackled the thorny problems posed by the ­long-­term chemical evolution of the crust. Ancient crust is sparsely exposed and affected by weathering alteration and is thus subject to serious sampling biases. Her group dealt with both problems by analyzing ancient glacial tills, rather than sampling ­water- or ­wind-­transported sediments, and developing ­weathering-­resistant chemical proxies to show that ancient continents were richer in Fe and Mg and contained less granitic material than today’s crust.

The Harry H. Hess Medal is intended to honor “outstanding achievements in research on the constitution and evolution of the Earth and other planets.” Roberta’s research scope and accomplishments fit that description perfectly.

—Albrecht W. Hofmann, Max Planck Institute for Chemistry, Mainz, Germany; also at Columbia University, New York

I am deeply moved and humbled by this tremendous honor. Science is not an individual pursuit; it is a collaborative endeavor, whether it be from “standing on the shoulders of giants” per Sir Isaac or through joint ventures with students and fellow scientists. That is why it is just a little embarrassing to stand here as an individual to be honored for accomplishments that reflect the work of so many. For over 3 decades, Bill McDonough and I collaborated on a wide variety of projects from the crust to the mantle and had many debates (yes, zirconium can and does fractionate from ­hafnium—I think I won a bottle of red on that one). The late Gao Shan, China University of Geosciences, Wuhan, who died far too early, was one of the most creative and inspiring scientists I have worked with. Together we explored the unusual happenings of the North China Craton, which introduced me to a fascinating part of the world and opened the door to many other collaborations. I feel that Shan’s enormous contributions were never adequately celebrated, and I hope that I can share this award with him posthumously. I have been fortunate to have worked with incredible students from whom I learned more than I taught. There is nothing more satisfying than to see your students go on to achieve at the highest levels: ­Cin-Ty Lee, ­Fang-­Zhen Teng, Jingao Liu, Xiaoming Liu (no relation), and Ming Tang, among others, keep me in awe of their intelligence, creativity, and overall kind spirits. They have become part of my extended family. I, in turn, benefited from mentoring from quite a few folks: Ross Taylor and Scott McLennan at Australian National University introduced me to the fascinating debate about continental crustal evolution and the use of sedimentary rocks to read the record of ancient Earth. Steve Goldstein, Al Hofmann, and the late Ted Ringwood all served as important mentors ­post-­Ph.D. I’ve had the good fortune to work in collaborative and supportive departments at the University of Maryland and now at the University of California, Santa Barbara. Finally, my family has supported me every step of the way: my brother Mike and sister Linda are here tonight with their families; my ­95-year-­old mother (Janet Rudnick) could not make it but continues to be an inspiration. My son, Patrick McDonough, is one of the finest humans I know. I thank you all, and those whom time does not permit me to mention by name, from the bottom of my heart. —Roberta Rudnick, University of California, Santa Barbara

Roberta Rudnick received the N. L. Bowen Award at the 2006 AGU Fall Meeting. The award recognizes outstanding contributions to volcanology, geochemistry, or petrology.  

One sign of a great scientist is that he or she uses fundamental observations in nature or experiments to drive questions and hypotheses on how natural processes work. Roberta satisfies all of these criteria, and more.

Working as a graduate student with Roberta, I came away with a deep appreciation for the value of having data. One example of this philosophy was Roberta’s seminal paper on the average composition of the continental crust, which has stood the test of time. But coming up with an estimate of the composition of a reservoir was really just a step in Roberta’s grander goals of answering the question of how the continents formed. The problem is that this question is too vague to mean anything to the noninitiated, and to the experts, the question is ill-posed because continent formation is so complicated that there seems to be no simple answer. It is in these circumstances where Roberta shines the most.

Roberta has the uncanny ability to see the big picture by synthesizing and distilling seemingly disparate details into a well-organized and clear message. A good example of this is Roberta’s 1995 paper “Making continental crust.” Although this was a review paper, Roberta formulated some of the most important questions or controversies in the field in a concise manner. Most review papers are just summaries of current paradigms, and after 10 years, they stop being cited or are replaced by new review papers. Roberta’s paper, however, continues to be cited, a reflection that much research right now is still driven by the questions that Roberta so elegantly laid out.

Finally, an enviable characteristic of Roberta is that she’s always exploring various tools to answer her questions. She appreciates the need to be interdisciplinary: Witness her various papers with geophysicists on the thermal state of continents and deep lithospheric evolution. She also systematically explores new techniques and new isotopic systems, as exemplified by her contributions to laser ablation ICP-MS, osmium isotopes, and now lithium isotopes, all to address specific issues on continent formation and dynamics. There is thus no doubt that Roberta is one of our great leaders and communicators in the field of geochemistry.

I will end my citation on a more personal note. When I came as a student to work with Roberta, even though I thought I knew a lot, I didn’t really know how to do science. By simply being her apprentice, I learned from Roberta how to be a scientist. Roberta has been and continues to be an inspiration and role model to so many of us. It is thus fitting that she is one of this year’s recipients of the N. L. Bowen Award.

—Cin-Ty A. Lee, Rice University, Houston, Texas

Thank you, Cin-Ty. I am honored and thrilled to have been selected for the N. L. Bowen Award. Like others, my interest in geology stemmed from an excellent class, this one in high school, which led me to pursue a geology degree at Portland State University. There I met Bill McDonough, and together we pursued master’s degrees with Denny Nelson at Sul Ross State University. The award of a U.S. National Science Foundation graduate fellowship literally opened the world to me, so Bill and I headed Down Under for Ph.D. study. Our years at the Australian National University were truly golden. With excellent colleagues, unsurpassed analytical equipment, and a cadre of fellow graduate students who were doing exciting research (and really knew how to party) we learned what research science was all about. Ross Taylor, my Ph.D. supervisor, had worked with Scott McLennan on the composition of the upper continental crust and published a model for the crust composition in their famous 1985 book. After solving the upper crust, Ross recognized the uncertainties in the lower crust composition and suggested I work there. So that’s what I did, and have been working on this topic, and the implications of the crust composition for Earth dynamics, ever since. Following ANU we spent 2 years in Mainz, Germany, with Al Hofmann and his group at the Max Planck Institute. Working closely with Steve Goldstein, I delved into Pb isotopes, and we discovered that the lower crust is not as unradiogenic as supposed, with implications for the Pb paradox, which is still not solved so many years later. Returning to ANU for a 5-year research fellowship with Ted Ringwood, my research focus moved a little deeper, into the upper mantle. My ANU days culminated in a paper on the composition of the lower crust, with David Fountain, and a new model for the crust’s composition. However, the most important collaboration I had while at ANU was with Bill: the arrival of our son, Patrick, who has been a joy in our lives and keeps us balanced (at least a little). My time at Harvard, and my move to Maryland in 2000, have also been productive and exciting years. Highlights include mentoring great students (Cin-Ty Lee, Matthias Barth, and Fanzhen Teng) and developing a close collaboration with Gao Shan (Chinese University of Geosciences, Wuhan), with whom I’ve been discovering the extraordinary history of the North China craton. I owe a debt to our chair, Mike Brown, for his vision for our department and who has built an internationally recognized (and very collegial) geochemistry group, putting Maryland on the map. Finally, Bill McDonough has been my soul mate, cheerleader, mentor, and geochemical sparring partner for more than half my life. My journey has not been alone and would have been very different if our paths had not crossed so many years ago. —Roberta Rudnick, University of Maryland at College Park