George Wetherill | |
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| Born | (1925-08-12)12 August 1925 Philadelphia, Pennsylvania, US |
| Died | 19 July 2006(2006-07-19) (aged 80) Washington, D.C., US |
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| Children | Rachel Wetherill Sarah Wetherill Okumura George W. Wetherill III |
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| Fields | Astrophysics,geology |
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George Wetherill (August 12, 1925 – July 19, 2006) was an American physicist and geologist. He was the director emeritus of the department of terrestrial magnetism at theCarnegie Institution of Washington.[1][2]
In 2000, Wetherill received theJ. Lawrence Smith Medal from theNational Academy of Sciences "For his unique contributions to the cosmochronology of the planets and meteorites and to the orbital dynamics and formation of solar system bodies."[3]In 2003, Wetherill received theHenry Norris Russell Lectureship, the highest honor bestowed by theAmerican Astronomical Society, "For pioneering the application of modern physics and numerical simulations to the formation and evolution of terrestrial planets."[4]
George Wetherill was born on August 12, 1925, inPhiladelphia. Wetherill benefited from theG.I. Bill to receive four degrees, the Ph.B. (1948), S.B. (1949), S.M. (1951), and Ph.D., in physics (1953), all from theUniversity of Chicago. He did his thesis research on the spontaneousfission ofuranium, as well as nuclear processes in nature, as aU.S. Atomic Energy Commission Predoctoral Fellow.[5]
After receiving his Ph.D., Wetherill became a staff member at Carnegie's Department of Terrestrial Magnetism (DTM) in Washington, D.C. There, he joined an interdepartmental group who were working to date rocks using geochemical methods that measured naturalradioactive decay. This involved determining the concentration andisotopic composition ofinert gases such asargon, as well as the isotopes ofstrontium andlead.[1]
Wetherill originated the concept of the Concordia Diagram for the uranium-lead isotopic system; this diagram became the standard means for determining precise ages of rocks, and of detecting the possibility ofmetamorphism. It provides a basis for high-precisiongeochronology of rocks dating back through the history of the planet Earth.[1]
Wetherill was also a member of the Carnegie group that accurately determined the decay constants ofpotassium andrubidium, an effort that has also become fundamental to the measurement of geological time.[1][6]
Wetherill left DTM in 1960 to become a professor of geophysics and geology at theUniversity of California, Los Angeles. There, he served as chairman of the interdepartmental curriculum in geochemistry (1964-1968), and as chairman of the Department of Planetary and Space Sciences (1968-1972).[7]
At UCLA, Wetherill further explored techniques for age-dating, examining extraterrestrial material with radiometric chronology techniques tometeorite andlunar samples. At the same time, he began to theorize about the origin of meteorites. His studies concentrated on collisions between objects in theasteroid belt together with resonances between their motions and those of planets. He computed how these events could move material into Earth-crossing orbits to become meteorites or larger Earth-impacting bodies responsible for the devastating impacts that caused mass extinctions of the majority of living species, including the dinosaurs.[7]
Later, Wetherill, along with scientists elsewhere, proposed that a certain unusual class of meteorites was not asteroidal in origin but instead came from the planetMars. This was later confirmed by laboratory work elsewhere and is now well accepted.[7]
In 1975, Wetherill returned to Carnegie's Department of Terrestrial Magnetism as director. He remained director until 1991, when he became a staff member. At DTM, he began extending his research efforts into questions concerning the origin of the terrestrial planets--Mercury,Venus,Earth, andMars. He was stimulated by earlier studies byVictor Safronov (O. Yu. Schmidt Institute, Moscow), who showed that as a swarm ofplanetesimals coagulated into large bodies the swarm could evolve to produce a few terrestrial planets. Wetherill developed a technique to calculate numerically the orbital evolution and accumulation of planetesimal swarms, and he used the technique to reach specific predictions of the physical and orbital properties of terrestrial planets. His results agreed well with present observations.[8]
In addition to showing how the inner solar system formed, Wetherill's work provided the basis for a model of a giant-impact origin for theMoon[9] and the core of Mercury.[10] It also led to explanations for the isotopic abundances of present-day planetary atmospheres.[11]
Wetherill has shown thatJupiter plays an important role in the evolution of theSolar System; by ejectingcomets from the Solar System, it offers a protective presence to the inner planets.[7] Wetherill's theoretical work supports discussions on the origins of the Solar System as well as onextrasolar planets.[12][13]
Wetherill provided leadership in the scientific community by serving on advisory committees forNASA, theNational Academy of Sciences,[14] and theNational Science Foundation. For 15 years, he was editor of theAnnual Review of Earth and Planetary Sciences.[15]
He served as president of theMeteoritical Society, theGeochemical Society, the Planetology Section of theAmerican Geophysical Union, the International Association of Geochemistry and Cosmochemistry,[16] and was a member of theAmerican Philosophical Society.[17]
Wetherill died at his home inWashington, D.C., on July 19, 2006, aged 80, after a long illness.[18][19]
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