Robert N. Clayton Enrico Fermi Distinguished Service Professor Emeri

Born Hamilton, Ontario, 1930.
Queen's University, Kingston, Ontario, S.B., 1951; S.M., 1952.
California Institute of Technology, Ph.D., 1955; Research Associate, 1955-56.
Pennsylvania State University, Assistant Professor, 1956-58.
The University of Chicago, Professor, 1958-.
Joint Appointment in the Department of Geophysical Sciences.


Member, National Academy of Sciences.
Fellow, American Association for the Advancement of Science.
Fellow, Royal Society of London.
Fellow, Royal Society of Canada.
Fellow, American Academy of Arts and Sciences.
Fellow, Meteoritical Society.
Fellow, American Geophysical Union.
2004 Recipient of the National Medal of Science.
1995 Urey Medal, European Association of Geochemistry.
1992 Award in Nuclear Chemistry, American Chemical Society.
1990 Honorary D.Sc., McMaster University.
1987 William Bowie Medal, American Geophysical Union.
1985 Elliot Cresson Medal, Franklin Institute.
1982 Leonard Medal, Meteoritical Society.
1981 Goldschmidt Medal, Geochemical Society.
1980 George P. Merrill Award, National Academy of Sciences.
1976 NASA Exceptional Scientific Achievement Medal.
1963-1965 Alfred P. Sloan Fellow.
1963-1964 Guggenheim Fellow.

OFFICE: RI 440, 5640 S Ellis Ave, Chicago, IL 60637

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The chemical processes by which cold, dark molecular clouds evolve into stars and planetary systems can be studied through isotopic analyses of primitive materials of our solar system: comets, asteroids, and interplanetary dust. These are represented primarily by components found in meteorites. Some nuclides provide information on time-scales, such as 26Mg produced by β-decay of 26Al; others can be directly related to earlier stages of stellar nucleosynthesis, such as 48Ca, 50Ti, and 54Cr from supernova events. Oxygen isotopes play a unique role in serving as a chemical tracer for solar nebular processes, and exhibit characteristic "isotopic anomalies" representing isolation of various chemical reservoirs on scales with dimensions ranging from micrometers (individual crystals) to thousands of kilometers (planets).

The cosmochemical issues addressed by meteorite studies bear directly on the origin of the planets and the initial conditions of formation of the Earth, particularly including its initial thermal state and the abundance and distribution of its internal energy sources. Isotopic studies of terrestrial materials are widely used to study the evolution of the Earth's major chemical systems: core, mantle, crust, ocean, atmosphere up to the present time. Studies of sulfur isotopes in photochemical reactions may bear on the early evolution of our oxygen-rich atmosphere.

Major advances in isotopic cosmochemistry and geochemistry depend on the development of ever better techniques for precise isotopic analysis of very small samples. We pioneered in the use of the ion microprobe, a device based on "secondary-ion mass spectrometry," for determination of elemental and isotopic abundances of elements at low concentrations in microscopic samples. We are now collaborating with a research group at the Argonne National Laboratory in the application of "resonance ionization mass spectrometry" in measuring the products of stellar nuclear reactions as recorded in "stardust": micrometer-sized mineral grains that were formed in or around stars, and were delivered to Earth inside meteorites. These provide direct experimental evidence of nucleosynthesis in red-giant stars and supernovae.

Selected References

Self-shielding in the Solar Nebula, Nature, 415, 860 (2002).

The Accretion, Composition, and Early Evolution of Mars, Space Science Reviews, 96, 197 (2001).

Chemical and Isotopic Fractionation During the Evaporation of the FeO-MgO-SiO2-CaO-Al2O3-TiO2 Rare Earth Element System, Geochimica et Cosmochemica Acta, 65, 479 (2001).

Oxygen Isotope Studies of Carbonaceous Chondrites, Geochimica et Cosmochimica Acta, 63, 2089 (1999).

Evaporation of Single Crystal Forsterite: Evaporation Kinetics, Magnesium Isotope Fractionation, and Implications of Mass-Dependent Isotopic Fractionation of a Diffusion-Controlled Reservoir, Geochimica et Cosmochimica Acta, 63, 953 (1999).

Zirconium and Molybdenum in Individual Circumstellar Graphite Grains: New Isotopic Data on the Nucleosynthesis of Heavy Elements, Astrophysical Journal, 504, 492 (1998).