In 1965, a Caltech geochemist found Americans carried more than 100 times natural blood lead; in 1996, the United States banned leaded gasoline in cars

Clair Patterson, a geochemist at Caltech, was trying to measure the age of the Earth when he ran into a different problem. He spent years developing contamination-controlled methods for measuring trace amounts of lead, as documented by Caltech. When he applied the methods to ocean sediments, he concluded that human activity had greatly increased the movement of lead through the environment, according to the National Academy of Sciences biographical memoir Clair Cameron Patterson by George R. Tilton.In 1965, he set out the implications in Contaminated and Natural Lead Environments of Man, published in Archives of Environmental Health. The paper argued that industrial lead had already exceeded natural background levels. Patterson compiled the amounts of industrial lead entering the environment from gasoline, solder, paint and pesticides and compared them with the natural flow.