RJ
Member Since 1983
Richard J J. Walker
Distinguished University Professor, University of Maryland College Park
Professional Experience
University of Maryland College Park
2012 - Present
University of Maryland College Park
Distinguished University Professor
1990 - Present
Education
Doctorate
1984
Honors & Awards
Harry H. Hess Medal
Received December 2019
Richard J. Walker was awarded the 2019 Harry H. Hess Medal at AGU’s Fall Meeting 2019 Honors Ceremony, held on 11 December 2019 in San Francisco, Calif. The medal is for “outstanding achievements in research on the constitution and evolution of the E...
Richard J. Walker was awarded the 2019 Harry H. Hess Medal at AGU’s Fall Meeting 2019 Honors Ceremony, held on 11 December 2019 in San Francisco, Calif. The medal is for “outstanding achievements in research on the constitution and evolution of the Earth and other planets.”  
Citation

Richard J. Walker is the world leader in the field of highly siderophile (or iron-loving) element geochemistry. While this may sound rather esoteric, the impact of Walker’s geochemical and cosmochemical research has changed how we look at Earth’s history, both from the outside in and from the inside out. He developed the rhenium-osmium isotopic method to map—for the first time—the age and evolution of the lithospheric mantle and its domains. Using the same isotopic tool kit, he was able to elucidate the planet’s late accretionary history and was among the first to demonstrate that asteroidal cores, sampled by some iron meteorites, formed very early in solar system history. He further pioneered the use of the platinum-osmium isotope system to test models of Earth’s core-mantle interaction and to refine core crystallization histories of iron meteorite parent bodies. Walker’s group pioneered measurements of tungsten isotope anomalies in early Earth rocks and mantle-derived magmas, demonstrating that primordial materials—formed in the first 50 million years of solar system history—astonishingly survived inside Earth for billions of years and are tapped now by mantle plumes rising from great depths. His group’s most recent discovery that the amount of isotopically anomalous tungsten correlates with that of primordial helium in “hot spot” volcanoes from Hawaii and Iceland has lit the field on fire. This observation implies that primordial materials that formed the first tens of millions of years after initial accretion of the planet remain today sequestered at or near the core-mantle boundary. This research, which requires cutting-edge, high-precision isotope ratio measurements, is a game changer and may reflect diffusive exchange between the deep mantle and the core.

Rich Walker’s impact goes well beyond these scientific discoveries, as he has been an excellent educator and mentor to a myriad of graduate students and postdoctoral scholars, most of whom have gone on to establish themselves in academia, thus representing the next generation of “siderophiles.” Finally, he has devoted significant time, energy, and resources to the University of Maryland (his academic home for the past 30 years), where he is currently the chair of the Department of Geology. Walker has fittingly served as the core of the geochemical community at Maryland, where he has been instrumental in accreting world-class colleagues to the institution, thereby making Maryland a bright center of the geochemical and cosmochemical universe.

For these stellar achievements, we honor Richard J. Walker with the 2019 Harry H. Hess Medal of AGU.

—Alan Jay Kaufman, University of Maryland, College Park; and Roberta L. Rudnick, University of California, Santa Barbara

Response
I’d like to start off by thanking those persons who nominated and selected me for this great award. I am much humbled by this recognition, but I sure do appreciate it! I also want to acknowledge the contributions of numerous postdocs and students, as well as other colleagues at the University of Maryland and beyond. I am fortunate to have worked with a dazzling array of accomplished individuals over the years. All that has been accomplished in my lab has been a result of a team effort. I am not permitted enough words or time to thank everyone individually here, so I offer a blanket, heartfelt thanks! Perhaps the real stars of this show are the siderophile elements. I am grateful to V. M. Goldschmidt for placing these elements in their own special geochemical category. Due to the difficulties associated with measuring many of these elements, they were somewhat neglected during the first few decades of “modern geochemistry.” During that period, only a few brave souls, such as my early mentor John Morgan, sought to lay the critical groundwork for these elements and map out many of the applications we are pursuing today. The siderophile elements are now a fertile ground for much contemporary geochemical and cosmochemical research. I began work on two siderophile elements, rhenium and osmium, while a postdoc in the mid-1980s. At the time, there were few data published for the associated isotope system, so exploring it seemed like a good thing to do. Studies involving the system are now quite common, and it is applied to a much wider range of problems than we ever envisioned in the 1980s. Accompanied by improvements to chemical separation techniques and mass spectrometers, my group has grown our list of favorite siderophile elements to include tungsten, ruthenium, and molybdenum. These elements are especially interesting because of their participation in short-lived radioactive decay systems and because their nucleosynthetic variability allows their use in tracing planetary genetics. The future is bright, as there is much yet to be learned from this group of elements. To end I would like to acknowledge and especially thank my wife, Mary Horan. Much of the research I have been involved with over the decades has been supplemented by data provided by her, all the while many of our dinner conversations have strayed into discussions of arcane geochemical issues. Much of what I’ve accomplished would not have been possible without her contributions. Thanks again to all! —Richard J. Walker, University of Maryland, College Park
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Reginald Daly Lecture
Received December 2016
Union Fellow
Received January 2009
Publications
AGU Abstracts
182W-142Nd anomalies in ancient and modern rocks reflect multiple primordial mantle processes
AGU 2024
study of earth's deep interior | 11 december 2024
Richard J. Walker
The 182Hf→182W and 146Sm→142Nd short-lived systems are characterized by half-lives of ~9 and 103 Myr, respectively. Positive and negative anomalies pr...
View Abstract
Tungsten-182 isotopic systematics of the Hawaiian mantle plume
AGU 2024
volcanology, geochemistry and petrology | 09 december 2024
Lori N. Willhite, Val Finlayson, Nicole Williamson...
Negative µ182W values in ocean island basalts (where µ182W is the deviation in 182W/184W from standards, in ppm) may result from isotopic equilibratio...
View Abstract
Mass-Independent Osmium Isotopic Compositions of Bulk Planetesimals
AGU 2024
planetary sciences | 09 december 2024
Kiran Almas, Richard J. Walker
Mass-independent nucleosynthetic signatures can serve as genetic markers that distinguish between materials from the inner and outer Solar System, des...
View Abstract
Check out all of Richard J J. Walker’s AGU Research!
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