Clair C. (Pat) Patterson, 73, passed away unexpectedly at his home in Sea Ranch, Calif., on December, 5, 1995. Pat left behind one of the most prolific and influential legacies, not only in geochemistry, but in environmental biogeochemistry as well. In geochemistry, he is best known for first establishing the true age of the Earth and solar system at 4.6 billion years, a date the accuracy of which has survived four decades. This inherently accurate geochronology arose from Pat's development of stable lead isotope techniques clean enough to overcome contaminated and erroneous results of earlier workers. This allowed him to further develop lead isotope systematics for divulging the evolution of the crust and mantle.