‘Cosmos’ recap: Getting a fix on Earth’s age, and the danger of lead


It’s often said that science can be a double-edged sword, used for good or ill. The same can be said for a material like lead, as we learn in this week’s “Cosmos.”

The time: 1966. The place: Pasadena, where a Caltech geochemist named Clair Patterson (“Pat” to his friends) is walking down a city street, clearly anxious as he sees “danger from an invisible menace” everywhere — which the animated teaser portrays as purple splotches contaminating surfaces everywhere. Patterson’s research on determining the true age of the Earth had revealed a grave threat to human health — and over the course of the episode, we’ll find out just what that threat is, and why Patterson fought so passionately all his life to get the powers that be to address it.

But first, a mini crash course in the foundation for Patterson’s work is in order. Many scholars over the centuries had pondered just how old our Earth might be, including an Irish archbishop named James Ussher. Ussher started with the Bible, specifically the account of the death of the Babylonian king Nebuchadnezzar II in the Second Book of Kings. By tracing the various biblical genealogies — what host Neil de Grasse Tyson calls “counting the begats” — he triumphantly declared that the Earth was born on October 22, 4004 BC, at 6 p.m. on a Saturday.


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That is certainly specific; it is also spectacularly wrong. One is reminded of Galileo’s observation about the dangers of using the Bible as a guide to scientific questions. Loosely paraphrased: The Bible teaches us how to get to heaven; it is not a treatise on how the heavens move.

Later scholars turned to the book of nature to unlock secrets that would shed light on Earth’s age, specifically the many layers of rock and sediment that represent various epochs in Earth’s geological history. Instead of counting the begats, scientists could count the layers. But even that method didn’t prove accurate enough.

A fragment of meteorite retrieved from Canyon Diablo held the answer. Such objects are relics from the formation of the solar system, including Earth, and they contain many different elements, notably uranium, a radioactive substance that over time decays into lead. In the 1940s, a physicist at the University of Chicago named Harrison Brown thought it might be possible to determine the age of the Earth by counting the lead isotopes in such a meteorite.

Brown assigned his young protégé, Clair Patterson, the task — at which point the narrative pauses to give us another sequence of Patterson, now older, freaking out in the aisle of a grocery store over a can of condensed milk as visions of purple blotches continue to dance before his eyes.

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Next we get another long, animated sequence in which Harrison assures young Patterson that it should be a trivial task to measure the amount of lead in a bunch of zircon crystals, and using that metric to determine the state of the earth: “It’ll be like duck soup!” (I’m assuming the writers are paraphrasing here. Creative license!)

Hah! While another grad student, George Tilton, easily completed his task of measuring the uranium in the zircon crystals, Patterson’s experiments gave wildly fluctuating results. I loved this sequence. It captures the frustration at unforeseen obstacles that plague any good experiment; we usually see the successes, and almost never witness the many failures that came before. And yet those failures are a vital part of the discovery process.

Patterson correctly surmised that there had to be other sources of lead in the surrounding lab environment contaminating his experiments. His efforts to purify those surroundings eventually led him to build his own sterilized lab from scratch at Caltech — the world’s very first “clean room.” And finally, he was able to make an accurate measurement, calculating that the Earth was 4.5 billion years old.

It was a fantastic achievement, but his reward, as Tyson tells us, was “a world of trouble.” See, Patterson continued to study lead in the environment — and it set him on a collision with some very powerful people, because he found that there had been a significant increase in the amount of lead contamination in the atmosphere, in the soil, in the ocean, even in ice core samples extracted from Greenland. And that is bad, because although lead is a “natural” substance, it is highly toxic to humans, even in trace amounts. There is no such thing as a “safe” level of lead.

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Lead’s toxicity has been known since the days of Rome, when lead lined the Roman aqueducts and the engineer Vitruvius warned against using lead, observing that “water is much more wholesome from earthenware pipes,” since that from lead seemed to cause illness in the inhabitants.


In the 1950s, lead was used in all kinds of consumer products, including paint and canned goods. The worst form was tetraethyl lead (TEL), a common additive to gasoline in much of the 20th century, because it helped reduce knocks in the engine. But when it was first made, plant workers became seriously ill, hallucinating and exhibiting aggressive, often violent behavior. The lead fumes drove them mad.

But this didn’t stop the use of TEL in gasoline — not for long. As long as the level of exposure was limited, policy makers reasoned, it should be fine. And the gas companies had their own scientific expert, Robert Kehoe, making reassurances to that effect.

Patterson begged to differ, based on his finding much higher lead concentrations in surface layers of the ocean, or in ice cores, than in the deeper layers — an indication that something was adding far too much lead into the environment. He published those conclusions in the illustrious journal Nature — and the pushback began, in the form of discontinued funding.

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There was a period where Patterson was dismissed as a crank, but eventually his message got through. We no longer add lead to gasoline, and there has been a 75% reduction in environmental lead since those policies were implemented. As Tyson notes at the episode’s end, you can try all you like to confound the issues when science tells you something you don’t want to hear, “but in the end, Nature cannot be fooled.”

It’s a powerful and highly relevant message, delivered in the context of a compelling story. This time, the makers of Cosmos didn’t get carried away with packing as many cool facts and wow-factor visuals as possible into 45 minutes, muddling things for the viewer. Instead, everything is in service to the story. That’s why “The Clean Room” is the strongest, most coherent, and riveting episode yet. More like this, please!



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