Prof. Emeritus Robert N. Clayton, whose pioneering research on the chemistry of meteorites and lunar rocks helped shape the field of cosmochemistry, died on Dec. 30. He was 87.In the foreword of a book dedicated to Clayton, Smithsonian geologist Glenn MacPherson wrote that Clayton “could easily wear the name ‘Mr. Oxygen.’” Clayton pioneered the use of oxygen isotopes as “fingerprints,” creating a relatively simple test to distinguish meteorites from ordinary rocks as well as a revolution in the burgeoning field of cosmochemistry.
Clayton, the Enrico Fermi Distinguished Service Professor Emeritus in Chemistry, Geophysical Sciences and the Enrico Fermi Institute, joined the University of Chicago faculty in 1958. Early in his career, he studied lunar rocks retrieved by the Apollo missions. His breakthrough came when he tested meteorites for the isotope oxygen-17 in addition to the usually studied oxygen-16 and oxygen-18. To the surprise of everyone in the field, he found that the ratio of these isotopes was extremely unusual, very different from Earth rocks.
The finding offered a scientific mystery that is yet to be fully solved—and a straightforward test to identify meteorites. “It was a profound discovery,” said Prof. Andrew Davis, who chairs the Department of Geophysical Sciences at UChicago and first worked with Clayton as a postdoctoral scholar in the late 1970s, “and it paved the way for a whole new line of inquiry.”
Clayton’s results, published in a seminal 1973 paper, energized the emerging field of cosmochemistry, which uses chemistry as a way to learn not only about meteorite age, source and history but how the planets and bodies formed in the early solar system. Analyzing the isotopes in rock samples reveals information about the conditions under which that rock formed, and the oxygen-17 measurements showed that the meteorites formed by a very unusual chemical process or circumstance. What exactly those circumstances were, and their ramifications for our …