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Alfred O. C. Nier, a well-known geophysicist who is considered one of the founders of isotope geology, geochronology, and isotope geochemistry, died on May 16 after a car accident.

In 1938, Nier, working with a mass spectrometer, measured the isotopes of lead. His results allowed determination of the Earth's age at 5 b.y. In 1940 he used a mass spectrometer in his basement workshop at the University of Minnesota to identify uranium 235, a major step in the evolution of the atomic bomb. In 1943, he went to work on the Manhattan Project in Oak Ridge, Tenn., to develop the first atomic bomb.