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 The Carnegie Institution of Washington (the organization's legal name), known also for public purposes as the Carnegie Institution for Science (CIS), is an organization in the United States established to fund and perform scientific research. Th ...

, DC, USA. In 2000, Wetherill received the J. Lawrence Smith Medal from the National 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." In 2003, Wetherill received the Henry Norris Russell Lectureship, the highest honor bestowed by the American Astronomical Society, "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 university, private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park, Chicago, Hyde Park neighborhood. The University of Chic ...

. 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 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. This involved determining the concentration and isotopic composition of

inert gases An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

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 ...

, as well as the isotopes of strontium 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 ch ...

. It provides a basis for high-precision

geochronology Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is ...

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 atmosph ...

and rubidium, 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 S ...

. 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 and lunar 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 The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, c ...

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. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. 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,

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 f ...

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 (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 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 slightly less than one-thousandth t ...

plays an important role in the evolution of the

Solar System The Solar System Capitalization 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 ...

; by ejecting

comets A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

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 agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

, the National Academy of Sciences, 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 ...

. For 15 years, he was editor of the '' Annual Review of Earth and Planetary Sciences''. He served as president of the

Meteoritical Society The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials that further our understanding of the ...

, the

Geochemical Society The Geochemical Society is a nonprofit scientific organization founded to encourage the application of chemistry to solve problems involving geology and cosmology. The society promotes understanding of geochemistry through the annual Goldschmidt Co ...

, 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 a ...

, 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, National Academy of Sciences * 1977,

National Medal of Science The National Medal of Science is an honor bestowed by the President of the United States to individuals in science and engineering who have made important contributions to the advancement of knowledge in the fields of behavioral and social scienc ...

* 1981, Leonard Medal,

* 1984, G. K. Gilbert Award,

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. Hitch ...

* 1986, G. P. Kuiper Prize of the Division of Planetary Sciences of the American Astronomical Society * 1991, Harry H. Hess Medal of the

* 1997,

awarded by President Clinton * 2000, J. Lawrence Smith Medal, National Academy of Sciences * 2003, Henry Norris Russell Lectureship, 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