Obituary of George West Wetherill

George West Wetherill died July 19, 2006 in his Washington, D.C., home of a heart attack. Early in his career, Wetherill helped establish the field of radiometric geochronology, and later he became a leader in the theoretical understanding of planet formation. For these achievements, he received the National Medal of Science from President Clinton in 1997, and the top awards from a broad range of professional organizations, including the Leonard Medal (Meteoritical Society, 1981), the G.K. Gilbert award (Geological Society of America, 1984), the Harry H. Hess medal (American Geophysical Union, 1991), and the Harry Norris Russell Lectureship (American Astronomical Society, 2003).

Born in Philadelphia during the Perseid meteor shower of August 1925, George soon became fascinated by the natural world, but found that his interest in science led to conflicts with his religious studies. He stated I am sure my interest in these questions was stimulated at an early age by the knowledge that many people felt deeply about these things, rather than dismissing them as dry and boring scientific details of no practical value.¹

George enlisted in the US Navy during World War II, and then used his GI Bill benefits to enroll in 1946 in the University of Chicago, where a broad spectrum of basic physics was being applied to the study of the natural world. Though his basic training was in physics, George’s experience at Chicago included healthy doses of astronomy, chemistry, and geology. George’s third publication was on naturally occurring isotopic variations caused by secondary nuclear reactions instigated by the alpha-decay of uranium and thorium. These are now referred to as Wetherill reactions.

After graduating from Chicago, George was attracted to the Department of Terrestrial Magnetism (DTM) of the Carnegie Institution of Washington, where a group was being assembled to develop the radiometric clocks that would allow accurate ages to be determined for rocks. Intrigued by the fact that radiometric dating occasionally provided incorrect results, George first remeasured many important decay constants and then explored the effects of element diffusion in minerals. The latter work led him to create the Concordia diagram that simultaneously considers the decay of 235U to 207Pb and 238U to 206Pb. This diagram allows not only improved precision in age determination, but provides an internal check on whether or not the U-Pb system has been disturbed by metamorphism. The Concordia diagram remains the most commonly used approach for translating lead isotopic measurements into accurate ages for planetary and solar system events.

After assuming a Professorship at UCLA in 1960, a seminar by James Arnold on a new Monte Carlo technique for studying the evolution of meteorite orbits showed George a new path to return to his interest in the origin of meteorites (he was a teenage member of the American Meteor Society). George obtained a copy of Arnold’s program and used it to begin a second career investigating the dynamics of small bodies in the inner Solar System.

In 1975, George returned as Director of the DTM, where he expanded the focus of his research on the origin of meteorites to the formation of planets themselves. Wetherill espoused the wisdom that There are too many good questions in science to waste one’s time doing something that would soon be done elsewhere . George’s pioneering work showed how the huge number of rocky building blocks present in a typical protoplanetary disk will naturally assemble into a set of planets like those we see in the inner Solar System. Later, he demonstrated that the same process was thwarted in the asteroid belt by the dynamical influence of Jupiter and Saturn. Along the way, George found time to consider the origin of the Moon, the source of the late heavy bombardment, and the possible nature of extrasolar planets.

George Wetherill was a scientist of the highest caliber whose contributions fundamentally changed our understanding of the history of the Solar System. He also was an exemplary citizen, serving all the expected roles of a leader Director, Editor, Society President, Member of the National Academy while maintaining his devotion to his family and his appreciation of his ability to advance human understanding. His view on this issue is reflected in his statement fundamental science bears the burden of distilling the vast confusion of theory and empirical data into a form that makes it possible to pass it in usable form to the future, enabling gifted children to develop into scientific leaders while they are still young.¹

George West Wetherill

Physics Today