off to the University of Chicago as a freshman with a clear idea of pursuing studies in geology. World War II interrupted his education. He went off to an officer’s training program in the navy and eventually joined the fleet in Norfolk, Virginia. He returned to the University of Chicago after demobilization, and his future scientific life was shaped there.

After World War II the faculty of the University of Chicago, weary of their part in the development of the atomic bomb, turned to research in areas of the most esoteric sorts. With mass spectrometers in place, Harold C. Urey and his students, postdocs, and research collaborators delved into the arcane worlds of determining the warmth of an ocean 100 million years ago, determining the ages of rocks and the Solar System, and exploring the chemistry of the Universe. It was in this hotbed of national-defense-irrelevant research that Harmon Craig found himself. An undergraduate geology major at the University of Chicago, he was propelled into this world of geochemistry and cosmochemistry without waiting to get his undergraduate degree.

The measurement of ancient sea temperature depended on analyzing carbon dioxide released from calcium carbonate fossils and measuring the relative masses of carbon dioxide composed of 18O and 16O. The constancy of the carbon isotope loading on the carbon dioxide was tacitly assumed. Craig, for his thesis, measured the natural variability of 13C/12C to establish the baseline for all future studies involving the carbon system.

The independent discovery of natural radioactive 14C by W. F. Libby at the University of Chicago immediately led to the application of 14C to dating in archaeology and Pleistocene geology. The stable carbon isotope study from Craig’s thesis allowed for corrections due to mass fractionation and permitted the proper determination of radiocarbon ages

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