IN THE LATE 1940s, a graduate student at the University of Chicago named Clair Patterson(who was, first name notwithstanding, an Iowa farm boy by origin) was using a new methodof lead isotope measurement to try to get a definitive age for the Earth at last. Unfortunatelyall his samples came up contaminated—usually wildly so. Most contained something like twohundred times the levels of lead that would normally be expected to occur. Many years wouldpass before Patterson realized that the reason for this lay with a regrettable Ohio inventornamed Thomas Midgley, Jr.

Midgley was an engineer by training, and the world would no doubt have been a safer placeif he had stayed so. Instead, he developed an interest in the industrial applications ofchemistry. In 1921, while working for the General Motors Research Corporation in Dayton,Ohio, he investigated a compound called tetraethyl lead (also known, confusingly, as leadtetraethyl), and discovered that it significantly reduced the juddering condition known asengine knock.

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