Mark Harrison, who was a Carnegie Fellow in geochemistry at DTM from 1981 to 1982, was elected to the National Academy of Sciences today.  Harrison was one of 72 new U.S. members and 18 foreign associates from 15 countries.

Harrison came to DTM from the Research School of Earth Sciences of the Australian National University.  At DTM, his research involved the partitioning and diffusion kinetics of trace elements in mantle-related mineral-melt systems.

Harrison is best known for his theoretical development and application of the Ar-Ar system as a thermochronometer.  He laid out the diffusion characteristics of Ar in a variety of minerals that allowed the decay of ⁴⁰K to ⁴⁰Ar to be used to measure the time since a mineral cooled below its closure temperature.  His applications of this technique ranged from studies of large-scale deformation in the Himalaya to the thermal evolution of oil-bearing basin sediments.  Harrison later pioneered the study of zircon grains up to 4.4-billion years old found in sediments in western Australia.  Characteristics of those zircons provide important constraints on conditions on the early Earth, including the inference that Earth's surface was sufficiently cool 4.4 billion years ago that oceans were present and stable.

Harrison is currently the Director of the Institute of Geophysics and Planetary Physics, and Professor of Geology at the Department of Earth and Space Sciences, at the University of California, Los Angeles.