Clair Patterson, Rocks from Space, and Metal in the Air

It’s not a secret that I’ve got a soft spot for meteorites, especially the sort that I can get my hands on and turn into jewelry.


Since meteorites are samples of the universe outside our atmosphere they are kind of by definition awesome, excepting the occasional mass extinction event causation. But humans are knowingly creating the current age of mass extinction, so who are we to throw stones at non-sentient space rocks?


Clair Patterson

A scientist named Clair Patterson (1922-1995) used meteorites to help determine the age of the earth. In studying them to learn about our home, he discovered a much closer and more personal problem-atmospheric lead.


He was a geochemist that spent years developing and refining his doctoral advisor’s method for finding the age of the earth. He used uranium-lead, then lead-lead dating methods on meteorite samples, including the Canyon Diablo meteorite. (An iron meteorite that impacted in what is now Arizona around 50,000 years ago and left fragments all around the impact crater.)


At the University of Chicago Harrison Brown came up with a method for counting lead isotopes in rocks to calculate the age of the Earth. As Bill Bryson wrote in his A Short History of Nearly Everything, “Realizing that the work would be exceedingly tedious, he assigned it to young Clair Patterson as his dissertation project. Famously he promised that determining the age of the Earth with his new method would be ‘duck soup.’ In fact, it would take years.”

Patterson at Caltech


Patterson started his work in 1948 and took it with him when he went to Caltech in 1952.


It involved making very precise measurements in extremely old rocks. One problem was that they had trouble finding rocks old enough


(Odd as it is to think today, they didn’t know yet just why surface rocks were younger than the planet yet.)


So Patterson made the leap and assumed (correctly) that meteorites were leftovers from the creation of the solar system, so they would be the same age as the earth.


A slice of Canyon Diablo meteorite fragment. “Canyon Diablo meteorite, pattern” by James St. John – Flickr: Canyon Diablo Meteorite. Licensed under Creative Commons Attribution 2.0 via Wikimedia Commons –

In 1953 he finally got specimens of the Canyon Diablo meteorite and access to a mass spectrometer to study and age them.


Shortly afterwards he announced his findings that Earth was around 4.55 billion years old, which is still the number we use today.


How did he date the samples? I’m not too good with radiometric dating so a super short and simple version:


For uranium-lead dating: Uranium is an unstable element that decays into lead. So by studying the ratio of uranium to lead atoms and using known rates of decay you can tell how long the uranium has been decaying and date something really ancient to the time of its creation.


Lead-lead dating is used less often now, but was an essential part of his study. The thing to know here is that elements have different isotopes.  Isotopes are different versions of the same element. They’ve got almost the exact same properties except for slightly different weights.


Depleted uranium. Theo Gray.

As Sam Kean puts it in The Disappearing Spoon, “Each type, or isotope, has a different atomic weight-204, 206, or 207. Some lead of all three types has existed since our supernova birth, but some has been created fresh by uranium. The catch is that uranium breaks down into only two of those types, 206 and 207. The amount of 204 is fixed, since no element breaks down into it.”


So to determine a sample’s age he could compare the ratio of lead isotopes created by decay to those that occur naturally.


He used three different stony and 2 different iron meteorites to determine the age of the earth. Why both types? Uranium doesn’t mix with iron, but lead does. So iron meteorites retain the original lead isotope proportions, since they didn’t contain any uranium to add new lead atoms.


Another problem he kept running into was the sheer volume of lead contamination while he was doing his research. The meteorites were always contaminated with large amounts of atmospheric lead whenever they were exposed to air.

Uranium decays into Lead. The Pb used as its abbreviation has the same root as the word plumber. The 207.2 is an average weight between the isotopes. Photo, Theo Gray.


So once he established the age of the Earth, he began to look at all this atmospheric lead. He discovered that all research on lead’s effects on humans had been funded by the corporations that made lead additives.


It should not come as a shock then that the findings were neither truthful nor accurate. To quote Bryson again “In one such study, a doctor who had no specialized training in chemical pathology undertook a five-year program in which volunteers were asked to breathe in or swallow lead in elevated quantities. Their urine and feces were tested. Unfortunately, as the doctor appears not to have known, lead is not excreted as a waste product. Rather, it accumulated in the bones and blood-that’s what makes it so dangerous-and neither bone nor blood was tested. In consequence, lead was given a clean bill of health.”


Patterson wondered how much lead levels had increased over time. Industry said that the amount of lead in the environment had only doubled with its industrial usage.


EPA chart on atmospheric lead.

Patterson found that deep ocean water had 3-10 times less lead than surface water while other metal ratios remained steady.


Studying ice core samples from Greenland (plugs of ice frozen over the centuries that give a tiny sample of atmospheric conditions from the time when that snow or rain first fell) showed that lead levels started to rise steadily after it began to be used as an additive in gasoline. 90% of lead in the atmosphere was from lead in gasoline.


He found the source of the lead that was contaminating his samples, but he was concerned about the public health implications of all that lead and spent much of the rest of his life fighting to make sure the public knew about them.


He was battling large and wealthy corporations and individuals, so many research centers were closed to him.


(Plenty of them were supposed to be neutral, but then as now money and corporate interests trump good science, due process or public interest. Especially when one director was a Supreme Court judge and another an influential member of the National Geographic Society. )


Diagram of one lead isotope. The number of protons determines the element, the number of neutrons can vary slightly, and that’s what makes different isotopes of the same element.

He became a liability to schools, as companies began to pressure the institutions he worked for to fire him or shut him up.  He was excluded from a national research panel studying the effects of lead in 1971, which was particularly egregious since by then he was the foremost expert on the topic.


It was through his efforts that there was a clean air act of 1970 (though he reasonably felt it didn’t do enough or act fast enough) and that leaded gasoline was finally taken off the market in 1986.


He was also worried about the amounts of lead in soldering and paint. He that lead levels were much higher in canned than fresh foods. Again, it was a few orders of magnitude higher than what the food companies claimed. Appallingly, despite this, lead solder wasn’t removed from food containers in America until 1993! Interestingly, some studies hint that lead poisoning might have been a contributing factor to the rise in crime starting during the postwar era.


Thanks to him, while we still have a great deal more lead in our blood than those born before the twentieth century, by the late 1990s lead levels in blood have fallen 80% and are still falling.


Clair Patterson died in 1995.


Having looked up some of Patterson’s obituaries, several of which completely leave out his work in the public interest, I think Bryson gave him a better one:


“He didn’t win a Nobel Prize for his work. Geologists never do. Nor, more puzzlingly, did he gain any fame or even much attention from a half century of consistent and increasingly selfless achievement. A good case could be made that he was the most influential geologist of the twentieth century.”

1 Comment

Filed under Historical Facts and Trivia, Natural Science

One response to “Clair Patterson, Rocks from Space, and Metal in the Air

  1. Pingback: Happy National Fossil Day! | Magpie's Miscellany

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