Bernard J. Wood was awarded the 2013 Harry H. Hess Medal at the AGU Fall Meeting Honors Ceremony, held on 11 December 2013 in San Francisco, Calif. The medal is for “outstanding achievements in research on the constitution and evolution of Earth and other planets.”
Citation
As Harry Hess recognized over 50 years ago, mantle melting is the fundamental motor for planetary evolution and differentiation. Melting generates the major divisions of crust mantle and core. The distribution of chemical elements between solids, melts, and gaseous phases is fundamental to understanding these differentiation processes. Bernie Wood, together with Jon Blundy, has combined experimental petrology and physicochemical theory to revolutionize the understanding of the distribution of trace elements between melts and solids in the Earth. Knowledge of these distribution laws allows the reconstruction of the source compositions of the melts (deep in Earth’s interior) from their abundances in volcanic rocks. Bernie’s theoretical treatment relates the elastic strain of the lattice caused by the substitution of a trace element in a crystal to the ionic radius and charge of this element. This theory, and its experimental calibrations, brought order to a literature of badly scattered, rather chaotic experimental data that allowed no satisfactory quantitative modeling of melting processes in the mantle.
Recently, Bernie has expanded the scope of his work by adding partitioning on liquid metal-silicate equilibria and on mineral phases relevant to the lower mantle. Thus, Ca-perovskite, which hosts most of the calcium and aluminum in the lower mantle, partitions trace elements in a dramatically different fashion from what is seen in upper mantle minerals. The implications of this for the evolution of the deep mantle are potentially profound. These new studies offer a framework for understanding the melting processes that shaped the earliest evolution of the Earth, namely, core segregation and magma ocean formation and solidification.
Other major highlights to Bernie’s work include the classic 1986 paper of Bina and Wood showing that the 400-km seismic discontinuity in the mantle is a phase transition with thermodynamic properties such that the transition would not be smeared out by olivine solid solution and will therefore show up as a sharp discontinuity in seismic records. This work did much to lay to rest the need for a compositional boundary at that depth, at a time when there was still a heated debate over the nature of the major seismic discontinuities in the mantle.
Even earlier, Bernie became a leading authority in the petrology and thermodynamics of metamorphic reactions, especially their use as mineralogical thermobarometers. Thus, Wood and Banno’s geothermobarometer based on garnet-orthopyroxene-clinopyroxene relationships, published 40 years ago, is still widely used today.
Bernie’s love for thermodynamics resulted in the classic textbook Elementary Thermodynamics for Geologists by Wood and Fraser and three other books. He is one of the foremost petrologists of our time, one who has brought both theoretical and experimental petrology back to the forefront of Earth science. He has done this through his deep understanding of theory and experiment and their meaning for Earth processes and his leadership in merging petrology and geochemistry into a single discipline.
The Harry H. Hess Medal is an award designed to honor “outstanding achievements in research on the constitution and evolution of Earth and other planets.” This description fits Bernie like a glove.
—ALBRECHT W. HOFMANN, Max Planck Institute for Chemistry, Mainz, Germany
Response
President Finn, friends, and colleagues, I am truly delighted to accept the Hess Medal for 2013. It is difficult to express one’s feelings adequately on receipt of such a prestigious award, but a mixture of pride, humility, and thankfulness for a long and lucky career all occur. It did not start propitiously as my high school grades would only ensure undergraduate entry into the Northern Polytechnic, a second-tier institution in London. Nevertheless, I was enthused by several great teachers, including John Charalambous (inorganic chemistry) and Stephen Morel, a field geologist who had worked for many years in Malawi. They pushed me into trying for graduate school, and I was fortunate to find the eclectic Roger Strens my supervisor at Newcastle.
I finished my Ph.D. intrigued by the potential of combining thermodynamics with experiments to develop thermobarometers for peridotites and managed to get postdoc funding to do this in the experimental lab in Manchester. Later that year (1972), W. S. “Mac” Mackenzie called me into his Manchester office and told me he’d recommended me for a two-quarter position in Berkeley teaching metamorphic petrology. When I expressed doubts about my knowledge of metamorphism, he just said, “You only need to stay a week ahead of the students.” Fortunately for me, I went.
Berkeley in 1973 was an exhilarating place, buzzing with the aftermath of the anti–Vietnam War demonstrations and engrossed in the Watergate hearings. Ian Carmichael, who was chair, absorbed me into his group, and my education advanced rapidly during vigorous arguments with my office mate, Bruce Marsh, and with the occupants of Hal Helgeson’s “Prediction Central.” I returned to a faculty position in Manchester and was strongly supported to build an experimental program by my senior colleagues Jack Zussman and Mac.
In 1981 I moved to Northwestern and stayed for a very happy 8 years. Working next to a strong geophysics group and interacting with Seth Stein, I became interested in applying my thermodynamic and petrological knowledge to whole-Earth structure, particularly to seismic discontinuities and phase transitions. Sy Schlanger taught me the secrets of being an effective department chair. In addition, there was something about Northwestern that seemed to attract a range of interesting and talented graduate students, and they all helped to keep us on our toes.
In Bristol (1989) Steve Sparks and I worked closely on trying to build a high-quality department. Among others, we hired Jon Blundy, who collaborated successfully with me on trace element partitioning. I was again fortunate to work with a number of excellent graduate students, including the recent Macelwane awardee Dan Frost.
In the context of this award I should finish by mentioning an interview for a junior faculty job at Oxford in 1972. Ron Oxburgh asked how the direction of my “research would be influenced by plate tectonics.” I replied that I couldn’t think of any way it would be. I didn’t get the job! But I hope that Ron and Harry Hess would both think I’ve progressed since then.
Thank you all very much.
—BERNARD J. WOOD, University of Oxford, Oxford, UK