From Today In Science History:
Patterson (June 2, 1922 - December 5, 1995) was a U.S. geochemist who in 1953 made the first precise measurement of the Earth's age, 4.55 billion years. He is noted for providing the first reliable ages of the earth and meteorites (1962), using analysis of the isotopic compositions and concentrations of lead in terrestrial materials and meteorites.
He also established the patterns of isotopic evolution of lead on earth, by analysis of critical rocks, sediments and waters of the planet. Thus he created a powerful tool for identifying, tracing and evaluating the nature of the major geochemical reservoirs in the crust, mantle, and oceans.
Photo from HERE.