Carnegie Institution of Washington, Washington, D. C.
Ho-kwang Mao was awarded the 2007 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, which was held on 12 December 2007 in San Francisco, Calif.
The Inge Lehmann Medal is awarded in recognition of “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.” When Ho-kwang (Dave) Mao completed his Ph.D. in 1968 at the University of Rochester and moved to the Geophysical Laboratory, a revolution in how we could achieve that understanding was in the making.
Over the following four decades, Dave Mao redefined solid Earth geophysics, demonstrating that the mantle and core are accessible in the laboratory through direct study of their components at high pressures and temperatures. Through diverse, ingenious experimentation, this journey to the center of the planet has revealed the many dramatic ways that Earth materials transform under extreme conditions and established a materials-based understanding of the deep interior.
Dave’s first paper in JGR, based on his M.S. thesis, broke new ground in studies of the core by demonstrating polymorphism in iron alloys. This theme has continued throughout his career, leading to diverse studies of the phase diagram, equation of state, and optical, elasticity, and texture measurements, all at pressures of the core. Work on oxides and silicates that commenced with his Ph.D. thesis addressed the complete range of upper and lower mantle minerals. Dave and his group established the full suite of properties of silicate perovskites, including phase relations with accessory oxides and volatile components. His papers 30 years ago proposed that magnesium-rich silicate perovskite is the most abundant mineral in the planet, a paradigm that remains intact to this day. Recent work is revealing the nature of silicate postperovskite and the core-mantle boundary region.
Dave accomplished this by focusing on the development of instrumentation that could, first, recreate the entire range of pressures and temperatures of the deep interior, and, second, allow accurate measurements under those conditions. His revolutionary refinements of the diamond anvil cell with Peter Bell established that static megabar pressures could be achieved in the laboratory, and steadily advanced the range of accessible pressures to the inner core. A remarkable array of techniques were developed and applied, from lasers to synchrotron radiation to neutron methods. These accomplishments in experimental geophysics have been a windfall for other disciplines, leading to numerous discoveries beyond geoscience.
During my first experiments with Dave, I realized his key to success: an uncanny ability to distill a scientific problem into an experiment, to develop an appropriate technique, and to go into the lab and solve it, all with infectious enthusiasm and a generous spirit. Nearly every leading group in the field of static high-pressure research worldwide has benefited from contact with Dave, or from the people he has trained.
This is Dave’s first medal from AGU, surprising given his numerous other accolades, including membership in not one but three National Academies, his many other medals, and the fact that Dave identifies himself as a geophysicist. Since that first article in JGR, Dave has published some 683 papers with 411 different coauthors; countless others he has influenced directly or indirectly, all testament to a body of work that has profoundly influenced our understanding of the mantle and core. Moreover, this productivity and impact show no sign of deceleration. I present Ho-kwang Mao, the Lehmann Medalist for 2007.
—RUSSELL J. HEMLEY, Geophysical Laboratory, Carnegie Institution of Washington, Washington, D. C.
Thank you, Rus, for those kind words, and thanks to the rest of my colleagues, postdocs, and students at the Geophysical Laboratory and around the world with whom I have had the good fortune and pleasure to collaborate.
It is an honor to receive this medal, named after the extraordinary scientist who discovered the Earth’s inner core. The behavior of iron in lower mantle silicates and the core has been a key and constant thread throughout my career. I would like to thank my Ph.D. advisors, Bill Bassett and Taro Takahashi, who discovered the hexagonal close-packed iron in 1964, and introduced me to the diamond anvil cell. As Rus mentioned, the topic of my masters thesis–and of my first article published exactly 40 years ago was–the equation of state of iron alloys. I then had the good fortune to work with Peter Bell, developing the megabar diamond anvil cell together, and my first megabar article published in JGR in 1979 was on iron. I would also like to thank Rus Hemley for pushing physics and chemistry onto this geophysicist, which greatly expanded my horizon or depth in reaching 3 megabar and high temperatures with X-ray diffraction, imaging, and spectroscopy for crystal chemistry, crystal structure, seismic velocities, and rheological properties, again on iron.
Although there have been significant advances in the field of mineral physics in improving in situ characterization methods and reaching ever more extreme conditions, we still have not reached both inner core pressure and temperatures simultaneously. In the meantime, seismologists have made remarkable progress in increasing our understanding of the Earths deep interior. It is fitting that the first Lehmann medalist was Don Helmberger, who opened so many inner core challenges for us to tackle. Therefore I am accepting this medal as a challenge to all mineral physicists. We have a lot to do to help explain the complex and rich behavior observed in the most remote regions within our planet.
It is particularly apt that Inge Lehmann was a woman, since my life has been profoundly influenced by women. Among the many I would like to thank is my mother, who spurred me to pursue a career in science and would not be satisfied with anything less than excellence. My three daughters, Cyndy, Linda, and Wendy, have been a source of equal parts joy, pride, and befuddlement. My youngest daughter, Wendy, has been foolish enough to pursue a career in experimental mineral physics. Proving that the apple falls not far from the tree, her Ph.D. topic was on the behavior of iron in the D” layer and core.
Last, but far from least, I thank my lovely and patient wife, Agnes. To all who know me, it is clear that she is the real force behind my research and everything in my life. As proof, she had the good sense to forbid me from wearing a 30-year-old tuxedo I had been deluded into believing might still be a good fit. Alas, like the inner core, my midsection has grown a lot over time.
—HO-KWANG MAO, Carnegie Institution of Washington, Washington, D. C.