George Wetherill (August 12, 1925 Philadelphia, Pennsylvania – July 19, 2006 Washington, DC) was a physicist and geologist and the Director Emeritus of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, DC, USA. In 2000, Wetherill received the

J. Lawrence Smith Medal J. Lawrence Smith Medal is awarded every three years by the National Academy of Sciences for investigations of meteoric bodies. The medal is in honor of its namesake, the American chemist and meteoriticist, J. Lawrence Smith. Recipients Sour ...

from the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...

"For his unique contributions to the cosmochronology of the planets and meteorites and to the orbital dynamics and formation of solar system bodies." In 2003, Wetherill received the

Henry Norris Russell Lectureship The Henry Norris Russell Lectureship is awarded each year by the American Astronomical Society in recognition of a lifetime of excellence in astronomical research. The idea for the lectureship came from then society President Harlow Shapley in 1945, ...

, the highest honor bestowed by the

American Astronomical Society The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...

, "For pioneering the application of modern physics and numerical simulations to the formation and evolution of terrestrial planets."

Early life and education

George Wetherill was born on August 12, 1925, in Philadelphia, Pennsylvania. Wetherill benefited from the

G.I. Bill The Servicemen's Readjustment Act of 1944, commonly known as the G.I. Bill, was a law that provided a range of benefits for some of the returning World War II veterans (commonly referred to as G.I.s). The original G.I. Bill expired in 1956, bu ...

to receive four degrees, the Ph.B. (1948), S.B. (1949), S.M. (1951), and Ph.D., in physics (1953), all from the

University of Chicago The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...

. He did his thesis research, on the spontaneous fission of

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

, as well as nuclear processes in nature, as a

U.S. Atomic Energy Commission The United States Atomic Energy Commission (AEC) was an agency of the United States government established after World War II by U.S. Congress to foster and control the peacetime development of atomic science and technology. President ...

Predoctoral Fellow.

Career and achievements

Department of Terrestrial Magnetism, 1953-1960

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 natural

radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

. This involved determining the concentration and isotopic composition of inert gases such as

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

, as well as the isotopes of

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...

and

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

. 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 of

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...

. It provides a basis for high-precision geochronology of rocks dating back through the history of the planet Earth. Wetherill was also a member of the Carnegie group that accurately determined the decay constants of

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

and

rubidium Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...

, an effort that has also become fundamental to the measurement of geological time.

University of California, Los Angeles

Wetherill left DTM in 1960 to become a professor of geophysics and geology at the

University of California, Los Angeles The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California St ...

. 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). At UCLA, Wetherill further explored techniques for age-dating, examining extraterrestrial material with radiometric chronology techniques to

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...

and

lunar Lunar most commonly means "of or relating to the Moon". Lunar may also refer to: Arts and entertainment * ''Lunar'' (series), a series of video games * "Lunar" (song), by David Guetta * "Lunar", a song by Priestess from the 2009 album ''Prior t ...

samples. At the same time, he began to theorize about the origin of meteorites. His studies concentrated on collisions between objects in the asteroid 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. Later, Wetherill, along with scientists elsewhere, proposed that a certain unusual class of meteorites was not asteroidal in origin but instead came from the planet

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

. This was later confirmed by laboratory work elsewhere and is now well accepted.

Department of Terrestrial Magnetism, 1975-

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 Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, and

. He was stimulated by earlier studies by

Victor Safronov Viktor Sergeevich Safronov (russian: Ви́ктор Серге́евич Сафро́нов) (born Velikie Luki; 11 October 1917 in Russia – 18 September 1999 in Moscow, Russia) was a Soviet Union, Soviet astronomer who put forward the low-mass-n ...

(O. Yu. Schmidt Institute, Moscow), who showed that as a swarm of

planetesimal Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System a ...

s 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. 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 the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and the core of Mercury. It also led to explanations for the isotopic abundances of present-day planetary atmospheres. Wetherill has shown that

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

plays an important role in the evolution of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

; by ejecting comets from the solar system, it offers a protective presence to the inner planets. Wetherill's theoretical work supports discussions on the origins of the Solar System as well as on

extrasolar planets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

Community engagement

Wetherill provided leadership in the scientific community by serving on advisory committees for

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

, the

, and the

National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...

. For 15 years, he was editor of the ''

Annual Review of Earth and Planetary Sciences ''Annual Review of Earth and Planetary Sciences'' is an annual peer-reviewed scientific journal published by Annual Reviews, which broadly covers Earth and planetary sciences, including geology, atmospheric sciences, climate, geophysics, env ...

''. He served as president of the Meteoritical Society, the Geochemical Society, the Planetology Section of the

American Geophysical Union The American Geophysical Union (AGU) is a 501(c)(3) nonprofit organization of Earth, atmospheric, ocean, hydrologic, space, and planetary scientists and enthusiasts that according to their website includes 130,000 people (not members). AGU's act ...

, the International Association of Geochemistry and Cosmochemistry, and was a member of the

American Philosophical Society The American Philosophical Society (APS), founded in 1743 in Philadelphia, is a scholarly organization that promotes knowledge in the sciences and humanities through research, professional meetings, publications, library resources, and communit ...

. Wetherill died at his home in Washington, D.C Wednesday, July 19, 2006, after a long illness.

Awards

* 1974, Member,

* 1977, National Medal of Science,

* 1981,

Leonard Medal The Leonard Medal honors outstanding contributions to the science of meteoritics and closely allied fields. It is awarded by the Meteoritical Society. It was established in 1962 to honor the first President of the Society, Frederick C. Leonard. ...

, Meteoritical Society * 1984,

G. K. Gilbert Award The G. K. Gilbert Award is presented annually by the Planetary Geology Division of the Geological Society of America for outstanding contributions to the solution of fundamental problems in planetary geology in the broadest sense, which includes ge ...

Geological Society of America The Geological Society of America (GSA) is a nonprofit organization dedicated to the advancement of the geosciences. History The society was founded in Ithaca, New York, in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchco ...

* 1986, G. P. Kuiper Prize of the Division of Planetary Sciences of the

* 1991, Harry H. Hess Medal of the

* 1997, National Medal of Science awarded by President Clinton * 2000,

* 2003,

, American Astronomical Society

External links

Washington Post obituary

Carnegie Institution Bio

International Center for Scientific research

References

{{DEFAULTSORT:Wetherill, George 1925 births 2006 deaths 20th-century American physicists American nuclear physicists Members of the United States National Academy of Sciences National Medal of Science laureates University of California, Los Angeles faculty People from Philadelphia Annual Reviews (publisher) editors Members of the American Philosophical Society Presidents of the Geochemical Society