George Wetherill
Encyclopedia
George Wetherill was the Director Emeritus, Department of Terrestrial Magnetism, Carnegie Institution of Washington, DC, USA.
George Wetherill benefited from the G.I. Bill 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
. He did his thesis research, on the spontaneous fission
of uranium
, as well as nuclear processes in nature, as an U.S. Atomic Energy Commission
Predoctoral Fellow. Upon 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 of Carnegie scientists who were working to date the Earth's rocks by geochemical methods involving natural radioactive decay
. This involved determining the concentration and isotopic
composition of inert gases such as argon
, as well as the isotopes of strontium
and lead. He 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
, and it forms the basis for all high-precision geochronology
in rocks dating back to the early history of the Earth. He was also a member of the Carnegie group that accurately determined the decay constants of potassium
and rubidium
, an effort that has also become fundamental to the measurement of geological time.
Wetherill left DTM in 1960 to become a professor of geophysics and geology at the University 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). At UCLA, his interests in age-dating techniques expanded to include extraterrestrial material, as he began applying his radiometric chronology techniques to meteorite
and lunar
samples. At the same time, he began theoretical explorations into 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, he, along with scientists elsewhere, proposed that a certain unusual class of meteorites was not asteroidal in origin but instead came from the planet Mars
. This was later confirmed by laboratory work elsewhere and is now well accepted.
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
, and Mars
. He was stimulated by earlier studies by Victor Safronov (O. Yu. Schmidt Institute, Moscow), who showed that as a swarm of planetesimal
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
and the core of Mercury. It also led to explanations for the isotopic abundances of present-day planetary atmospheres. Recently, Wetherill has shown that Jupiter
plays an important role in the evolution of our solar system
; 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 our solar system as well as on extrasolar planets.
Wetherill provided leadership in the scientific community by serving on advisory committees for NASA
, the National Academy of Sciences
, and the National Science Foundation
. For 17 years, he was editor of the Annual Review of Earth and Planetary Sciences. He served as president of the Meteoritical Society
, the Geochemical Society
, the Planetology Section of the American Geophysical Union
and the International Association of Geochemistry and Cosmochemistry.
Wetherill died at his home in Washington, D.C Wednesday, July 19, 2006 after a long illness.
in 1974, the 1981 Leonard Medal
of the Meteoritical Society
, the 1984 G. K. Gilbert Award
of the Geological Society of America
, the 1986 G. P. Kuiper Prize of the Division of Planetary Sciences of the American Astronomical Society
, the 1991 Harry H. Hess Medal of the American Geophysical Union
, the 1997 National Medal of Science
awarded by President Clinton and the 2000 J. Lawrence Smith Medal
(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 was awarded the Henry Norris Russell Lectureship
, the highest honor bestowed by the American Astronomical Society.
George Wetherill benefited from the G.I. Bill 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
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
. He did his thesis research, on the spontaneous fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, as well as nuclear processes in nature, as an U.S. Atomic Energy Commission
United States Atomic Energy Commission
The United States Atomic Energy Commission was an agency of the United States government established after World War II by Congress to foster and control the peace time development of atomic science and technology. President Harry S...
Predoctoral Fellow. Upon 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 of Carnegie scientists who were working to date the Earth's rocks by geochemical methods involving natural radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
. This involved determining the concentration and isotopic
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
composition of inert gases such as argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, as well as the isotopes of strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
and lead. He 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
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
, and it forms the basis for all high-precision geochronology
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
in rocks dating back to the early history of the Earth. He was also a member of the Carnegie group that accurately determined the decay constants of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
and rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
, an effort that has also become fundamental to the measurement of geological time.
Wetherill left DTM in 1960 to become a professor of geophysics and geology at the University of California, Los Angeles
University of California, Los Angeles
The University of California, Los Angeles is a public research university located in the Westwood neighborhood of Los Angeles, California, USA. It was founded in 1919 as the "Southern Branch" of the University of California and is the second oldest of the ten campuses...
. 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, his interests in age-dating techniques expanded to include extraterrestrial material, as he began applying his radiometric chronology techniques to meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
and lunar
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
samples. At the same time, he began theoretical explorations into the origin of meteorites. His studies concentrated on collisions between objects in the asteroid belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
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, he, 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
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. This was later confirmed by laboratory work elsewhere and is now well accepted.
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 (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
, Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
, Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, and Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. He was stimulated by earlier studies by Victor Safronov (O. Yu. Schmidt Institute, Moscow), who showed that as a swarm of planetesimal
Planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger...
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
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
and the core of Mercury. It also led to explanations for the isotopic abundances of present-day planetary atmospheres. Recently, Wetherill has shown that Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
plays an important role in the evolution of our solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
; 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 our solar system as well as on extrasolar planets.
Wetherill provided leadership in the scientific community by serving on advisory committees for NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
, and the National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
. For 17 years, he was editor of the Annual Review of Earth and Planetary Sciences. He served as president of the Meteoritical Society
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 origin and history of the solar system.The...
, the Geochemical Society
Geochemical Society
The Geochemical Society is a nonprofit and international scientific society for the purpose of encouraging the application of chemistry to solve problems involving geology and cosmology...
, the Planetology Section of the American Geophysical Union
American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
and the International Association of Geochemistry and Cosmochemistry.
Wetherill died at his home in Washington, D.C Wednesday, July 19, 2006 after a long illness.
Awards
His awards include election to the National Academy of SciencesUnited States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
in 1974, the 1981 Leonard Medal
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....
of the Meteoritical Society
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 origin and history of the solar system.The...
, the 1984 G. K. Gilbert Award
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 geochemistry, mineralogy, petrology, geophysics,...
of the Geological Society of America
Geological Society of America
The Geological Society of America is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchcock, John R. Proctor and Edward Orton and has been headquartered at 3300 Penrose...
, the 1986 G. P. Kuiper Prize of the Division of Planetary Sciences of the American Astronomical Society
American Astronomical Society
The American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC...
, the 1991 Harry H. Hess Medal of the American Geophysical Union
American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
, the 1997 National Medal of Science
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 sciences, biology, chemistry, engineering, mathematics and...
awarded by President Clinton and the 2000 J. Lawrence Smith Medal
J. Lawrence Smith Medal
J. Lawrence Smith Medal is awarded by the National Academy of Sciences for investigations of meteoric bodies. The medal is in honor of its namesake, J. Lawrence Smith.-Further reading:* Willson, Lee Anne. Presented April 2006....
(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 was awarded the Henry Norris Russell Lectureship
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.-Previous lecturers:This list of lecturers is from the American Astronomical Society's website....
, the highest honor bestowed by the American Astronomical Society.