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Clair Cameron Patterson (June 2, 1922 – December 5, 1995) was an American geochemist. Born in Mitchellville, Iowa, Patterson graduated from Grinnell College. He later received his Ph.D. from the University of Chicago and spent his entire professional career at the California Institute of Technology (Caltech).
In collaboration with George Tilton, Patterson developed the uranium–lead dating method into lead–lead dating. By using lead isotopic data from the Canyon Diablo meteorite, he calculated an age for the Earth of 4.55 billion years, which was a figure far more accurate than those that existed at the time, and one that has remained largely unchallenged since 1956.
Patterson first encountered lead contamination in the late 1940s as a graduate student at the University of Chicago. His work on this subject led to a total re-evaluation of the growth in industrial lead concentrations in the atmosphere and the human body, and his subsequent activism was seminal in the banning of tetraethyllead in gasoline and lead solder in food cans.