Leaded gasoline

On December 9, 1921, Thomas Midgley Jr. discovered that tetraethyl lead eliminated the metallic pinging that limited engine performance—and set in motion a century of consequences no one foresaw. The adjacent possible had created an irresistible demand: Ford's assembly line produced two million Model Ts annually by the 1920s, each engine limited to compression ratios around 6:1 because higher compression caused destructive "knock." Midgley, working in General Motors' research laboratory under Charles Kettering, spent six years testing 33,000 compounds before finding that lead, added at just one part per 1,300, outperformed every alternative.

The chemistry of tetraethyl lead had been known since 1854, when a German chemist synthesized it—and declared it too deadly for commercial use. Midgley knew the risks. He suffered lead poisoning himself in 1922 and took an extended "vacation" in Miami to recover. Seven workers died at GM and DuPont manufacturing plants between 1923 and 1924. Staff were "depressed to the point of considering giving up the whole tetraethyl lead program." They did not.

GM and Standard Oil formed Ethyl Corporation in 1923, marketing the additive as "Ethyl" gasoline to avoid the word "lead." The cascade was immediate: compression ratios climbed to 12.5:1, engines gained power and efficiency, and aviation fuel reached 100 octane by 1938—giving RAF Spitfires and Hurricanes a decisive advantage over the Luftwaffe's 89-octane fuel in the Battle of Britain. By the 1950s, billions flowed annually to Ethyl Corporation.

The reckoning came slowly. Clair Patterson, a Caltech geochemist, published in 1965 that Americans carried lead burdens 100 times higher than pre-industrial ancestors, with atmospheric lead elevated 1,000-fold by automobile exhaust. The industry attacked his research for decades. It took until January 1, 1996 for the US to ban leaded gasoline for road vehicles. Algeria became the last country to exhaust its supplies in August 2021—exactly one century after Midgley's discovery. Environmental historian J.R. McNeill concluded that Midgley 'had more adverse impact on the atmosphere than any other single organism in Earth's history.'