The impact of geochemist Clair C. Patterson, PhD’51, who determined the age of the earth and fought lead pollution.


Research to determine the age of the earth eventually turned geochemist Clair C. Patterson’s painstaking attention from elemental traces in the universe’s original rocks to the manufactured toxins that kept car engines from knocking. Contaminated data on ancient samples inspired him to study the planet’s environment in oceans and polar ice. There Patterson, PhD’51, validated his theory about what skewed his earlier data, and also confirmed his worst fears: unnatural levels of lead were choking the atmosphere in the 1950s and ’60s, posing an imminent threat to human health.

Patterson’s study establishing the earth’s age at 4.55 billion years, presented in 1953, took more than five years and solved a mystery that had entranced and eluded scientists for millennia. By the time Patterson was 31, his contribution to knowledge surpassed what most people can claim in a lifetime. When he died in 1995, a colleague told the New York Times that his breakthrough stood as “one of the most remarkable achievements in the whole field of geochemistry.”

Pursuing that achievement revealed the troubling specter of a poisoned modern environment and prompted even more important work. The 1970 Clean Air Act and a global effort to remove lead from gasoline and other products grew out of the awareness his subsequent research and advocacy created. On the occasion of Patterson’s 1995 Tyler Prize for Environmental Achievement, marine chemist Edward Goldberg, PhD’49, said, “It is interesting to speculate on how many additional years of life to world citizenry” could be credited to him.

That number is impossible to know, but the impact of adding lead to gasoline, and of removing it decades later, provides measurable and compelling evidence for Patterson’s crusade. As Mother Jones reported in 2013, the rise in violent crime throughout the United States in the 1960s and 1970s, and its decline beginning in the 1990s, corresponds to lead’s prevalence in the atmosphere.

Lead is a neurotoxin, affecting the brain in ways that diminish IQ, disrupt neural communication, and decrease the size of the prefrontal cortex, inhibiting impulse control and motor functions. Nobody is immune, but the harm is especially acute in children’s developing brains, and the effects persist throughout life.

There is no safe level of lead in the human body, and although that stark fact is a recent revelation, the element’s dangers, at least in high doses, became apparent as soon as ancient Romans started extracting it. But because it was cheap and malleable—and because slaves and other laborers had the most direct contact—lead remained essential to many amenities. 

The Romans used it to line pipes and baths; the word “plumbing” comes from the Latin word for lead. They used it in cooking pots and even to sweeten wine. Exposure became widespread enough that historians consider lead’s toxic effects to be a factor in the fall of the empire. 

In the early 20th century, its increased use in consumer products was marketed as a great benefit. Advertisers produced a children’s nursery rhyme extolling the virtues of lead in light bulbs, galoshes, and paint.

Tetraethyl lead started to be used as a gasoline additive in the 1920s. The weapons-grade hazard it presented became horrifyingly prevalent. “Some of the workers who processed the stuff in factories in Delaware and New Jersey,” astrophysicist Neil deGrasse Tyson said on his 2014 program, Cosmos, “were going insane, hallucinating, jumping out of windows. They died screaming.”

Industry scientists acknowledged risks for workers who had regular contact with lead, but they assured the public that, as a naturally occurring element in the earth, it posed no general threat. This became accepted wisdom and for decades hardly anybody protested, even as atmospheric levels spiked.

Patterson himself first recognized lead contamination only as a research nuisance, complicating a project his University of Chicago mentor Harrison Brown had promised would be simple. “Duck soup,” he said.

Harrison Brown. (University of Chicago Photographic Archive, apf1-02288, Special Collections Research Center, University of Chicago Library)

Brown had come up with a concept for how to measure uranium and lead isotopes in igneous rock and he assigned Patterson and another student, George Tilton, SM’49, PhD’51, to develop the technique in the lab. Uranium ions in rock decay into lead at a known rate. Determining the ratio of uranium to lead in a rock would allow scientists to calculate its age. Brown posited that the process could also be applied to meteorites to determine the age of the earth.

Patterson explained why in a 1995 interview for the Caltech archives: “Brown had worked out this concept that the lead in iron meteorites was the kind of lead that was in the solar system when it was first formed, and that it was preserved in iron meteorites without change from the uranium decay, because there is no uranium in iron meteorites.”

Brown’s notion turned out to be correct, but establishing accurate lead levels turned out to be an unexpected challenge. “Above all,” writes Bill Bryson in A Short History of Nearly Everything (Broadway Books, 2003), “there was the problem that Patterson’s samples were continuously and unaccountably contaminated with large doses of atmospheric lead whenever they were exposed to air.”

He didn’t grasp why for a while. Frustrated, Patterson tried to treat his lab like a surgical suite, creating what may have been the first ever research “clean room” to protect his samples from lead exposure. This would allow him to isolate the naturally occurring levels in the rock more precisely, but the process remained slow.

While the project remained a work in progress, Patterson completed his UChicago PhD and followed Brown to Caltech. His big breakthrough came in 1953, working with UChicago physicist Mark Inghram, PhD’47. Using a high-tech mass spectrograph at Argonne National Laboratory, he bored down to the 4.55-billion-year answer once and for all. Seventy years of further research has only narrowed Patterson’s margin of error.

Mark Inghram, PhD’47. (University of Chicago Photographic Archive, apf1-05197, Special Collections Research Center, University of Chicago Library)

In the thrall of the accomplishment, his first stop was his childhood home in Iowa to tell his mother. The excitement overcame him, and he insisted that she take him to the hospital, fearing he was having a heart attack.

As understandable as his reaction was, it was also uncharacteristic. The previous seven years of deliberate but relentless work better embodied Patterson the scientist and the man. He was steady in his approach and so disinterested in credit that he routinely listed his name second on papers published with students to help advance their careers.

It was Patterson’s name that would become anathema in the lead industry, which was thriving at the time, leading to as much as 270,000 tons per year of automotive lead pollution. After his experience with contaminated labs, he developed a hunch that cars were pumping all that extra lead into the atmosphere, essentially injecting a toxin into everybody’s oxygen.

Lead does not decay. It accumulates in the air, in the water, in bone and blood, and it stays there forever, just like it did in the meteorites Patterson analyzed to date the planet. If, as he suspected, the mounting levels came from a source like car exhaust, people were inhaling a dire threat in amounts that increased every day, but the atmospheric accumulation also could be stopped.

To test his theory, Patterson went to sea. With funding from the American Petroleum Institute, he conducted an analysis that found much higher amounts of lead in shallow water than in the depths, a result that supported his hypothesis. The levels would have been more consistent if they were not a result of external contamination.

Following Patterson’s 1963 Nature paper detailing the data, petroleum industry leaders pressured him to cease studying the question, threatening to withhold their financial support. He persisted without it, drawing on sources such as the Atomic Energy Commission and the National Science Foundation.

Traveling to Greenland and Antarctica, Patterson drilled through ice laid in annual layers over thousands of years to gather more specimens, time machines for measuring lead levels at different points in history. His research revealed that the amount of lead in the atmosphere increased suddenly and dangerously beginning in about 1923.

Senator Edmund Muskie took notice. He convened hearings in 1966 in which both Patterson and industry expert Robert Kehoe testified. Kehoe insisted that lead levels in the environment had not increased and the amounts found in the human body were natural. 

Over time Patterson’s resolute opposition penetrated the consciousness and conscience of Congress and the public. Muskie shepherded the 1970 Clean Air Act unanimously through the Senate. By 1978 lead had to be removed from residential paint as its gradual phase out from consumer products continued. By January 1, 1996, it could no longer be used in the United States as a gasoline additive. As the reduction continued, children’s lead levels plummeted, falling 76 percent between 1978 and 1991.

Patterson mined material from the big bang to achieve the monumental task of dating the earth, but now his commitment to scientific truth made an immediate and far-reaching practical impact. He had added innumerable years to the lives of people in his own time, and long after.

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