Clair Patterson was born in 1922 in Iowa, finished high school at 16, studied chemistry at Grinnell, and learned to run a mass spectrometer at Oak Ridge during the Manhattan Project. After the war he joined Harrison Brown at the University of Chicago and worked with George Tilton on uranium-lead dating of zircon crystals to find the age of the Earth. Tilton’s uranium numbers made sense, but Patterson kept finding far too much lead, and it turned out to be coming from the lab itself: the glassware, the dust, the tap water and even his own hair.

At Caltech from 1952 he built one of the first ultra-clean laboratories, and in 1956 he used lead from the Canyon Diablo meteorite to date the Earth at 4.55 billion years. The contamination that had stalled his work then became his cause. Ocean water, ice cores and ancient bones showed that tetraethyl lead in gasoline had spread lead across the planet, and he took on industry scientist Robert Kehoe of the Ethyl Corporation in a long fight to get it banned.

• Why the core of a meteorite serves as a time capsule from the birth of the solar system
• Surface ocean water with up to 20 times the lead of deep water, using barium as a natural control
• Ice cores from Camp Century in Greenland in 1964 and from Antarctica the following year
• 1,600-year-old Peruvian skeletons showing modern bones held 700 to 1,200 times more lead, and canned tuna with 1,400 nanograms per gram
• His exclusion from a 1971 panel, a 78-page minority report in 1978, the U.S. ban by 1996 and blood lead falling up to 80 percent