If you were interested in finding out the ages of things, the University of Chicago in the1940s was the place to be. Willard Libby was in the process of inventing radiocarbon dating,allowing scientists to get an accurate reading of the age of bones and other organic remains,something they had never been able to do before. Up to this time, the oldest reliable dateswent back no further than the First Dynasty in Egypt from about 3000B.C. No one couldconfidently say, for instance, when the last ice sheets had retreated or at what time in the pastthe Cro-Magnon people had decorated the caves of Lascaux in France.
Remarkably, considering its startling toxicity, lead solder was not removed from Americanfood containers until 1993.
The problems of dating rocks were such that at one point almost everyone in the world hadgiven up on them. Had it not been for a determined English professor named Arthur Holmes,the quest might well have fallen into abeyance altogether.
dubious than others. This is particularly so with dates just around the time that people firstcame to the Americas, which is one of the reasons the matter is so perennially in dispute.
As Patterson increasingly became a liability to his institution, the school trustees wererepeatedly pressed by lead industry officials to shut him up or let him go. According to JamieLincoln Kitman, writing in The Nation in 2000, Ethyl executives allegedly offered to endow achair at Caltech “if Patterson was sent packing.” Absurdly, he was excluded from a 1971National Research Council panel appointed to investigate the dangers of atmospheric leadpoisoning even though he was by now unquestionably the leading expert on atmospheric lead.
Curiously, just as the technique was becoming widespread, certain flaws within it becameapparent. To begin with, it was discovered that one of the basic components of Libby’sformula, known as the decay constant, was off by about 3 percent. By this time, however,thousands of measurements had been taken throughout the world. Rather than restate everyone, scientists decided to keep the inaccurate constant. “Thus,” Tim Flannery notes, “everyraw radiocarbon date you read today is given as too young by around 3 percent.” Theproblems didn’t quite stop there. It was also quickly discovered that carbon-14 samples can beeasily contaminated with carbon from other sources—a tiny scrap of vegetable matter, forinstance, that has been collected with the sample and not noticed. For younger samples—those under twenty thousand years or so—slight contamination does not always matter somuch, but for older samples it can be a serious problem because so few remaining atoms arebeing counted. In the first instance, to borrow from Flannery, it is like miscounting by a dollarwhen counting to a thousand; in the second it is more like miscounting by a dollar when youhave only two dollars to count.
By the 1920s, when Holmes was in the prime of his career, geology had slipped out offashion—physics was the new excitement of the age—and had become severely underfunded,particularly in Britain, its spiritual birthplace. At Durham University, Holmes was for manyyears the entire geology department. Often he had to borrow or patch together equipment inorder to pursue his radiometric dating of rocks. At one point, his calculations were effectivelyheld up for a year while he waited for the university to provide him with a simple addingmachine. Occasionally, he had to drop out of academic life altogether to earn enough tosupport his family—for a time he ran a curio shop in Newcastle upon Tyne—and sometimeshe could not even afford the ￡5 annual membership fee for the Geological Society.
At all events, thanks to the work of Clair Patterson by 1953 the Earth at last had an ageeveryone could agree on. The only problem now was it was older than the universe thatcontained it.
Clair Patterson died in 1995. He didn’t win a Nobel Prize for his work. Geologists neverdo. Nor, more puzzlingly, did he gain any fame or even much attention from half a century ofconsistent and increasingly selfless achievement. A good case could be made that he was themost influential geologist of the twentieth century. Yet who has ever heard of Clair Patterson?
The technique Holmes used in his work was theoretically straightforward and arose directlyfrom the process, first observed by Ernest Rutherford in 1904, in which some atoms decayfrom one element into another at a rate predictable enough that you can use them as clocks. Ifyou know how long it takes for potassium-40 to become argon-40, and you measure theamounts of each in a sample, you can work out how old a material is. Holmes’s contributionwas to measure the decay rate of uranium into lead to calculate the age of rocks, and thus—hehoped—of the Earth.
It was known that snowfall in places like Greenland accumulates into discrete annual layers(because seasonal temperature differences produce slight changes in coloration from winter tosummer). By counting back through these layers and measuring the amount of lead in each, hecould work out global lead concentrations at any time for hundreds, or even thousands, ofyears. The notion became the foundation of ice core studies, on which much modernclimatological work is based.
In one such study, a doctor who had no specialized training in chemical pathologyundertook a five-year program in which volunteers were asked to breathe in or swallow leadin elevated quantities. Then their urine and feces were tested. Unfortunately, as the doctorappears not to have known, lead is not excreted as a waste product. Rather, it accumulates inthe bones and blood—that’s what makes it so dangerous—and neither bone nor blood wastested. In consequence, lead was given a clean bill of health.
Chlorofluorocarbons are also not very abundant—they constitute only about one part perbillion of the atmosphere as a whole—but they are extravagantly destructive. One pound ofCFCs can capture and annihilate seventy thousand pounds of atmospheric ozone. CFCs alsohang around for a long time—about a century on average—wreaking havoc all the while.
They are also great heat sponges. A single CFC molecule is about ten thousand times moreefficient at exacerbating greenhouse effects than a molecule of carbon dioxide—and carbondioxide is of course no slouch itself as a greenhouse gas. In short, chlorofluorocarbons mayultimately prove to be just about the worst invention of the twentieth century.
As for the other scourge left to us by Thomas Midgley, chlorofluorocarbons, they werebanned in 1974 in the United States, but they are tenacious little devils and any that youloosed into the atmosphere before then (in your deodorants or hair sprays, for instance) willalmost certainly be around and devouring ozone long after you have shuffled off. Worse, weare still introducing huge amounts of CFCs into the atmosphere every year. According toWayne Biddle, 60 million pounds of the stuff, worth $1.5 billion, still finds its way onto themarket every year. So who is making it? We are—that is to say, many of our largecorporations are still making it at their plants overseas. It will not be banned in Third Worldcountries until 2010.
Ozone is a form of oxygen in which each molecule bears three atoms of oxygen instead oftwo. It is a bit of a chemical oddity in that at ground level it is a pollutant, while way up in thestratosphere it is beneficial, since it soaks up dangerous ultraviolet radiation. Beneficial ozoneis not terribly abundant, however. If it were distributed evenly throughout the stratosphere, itwould form a layer just one eighth of an inch or so thick. That is why it is so easily disturbed,and why such disturbances don’t take long to become critical.
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.
Famously he promised Patterson that determining the age of the Earth with his new methodwould be “duck soup.” In fact, it would take years.
As for the Ethyl Corporation, it’s still going strong, though GM, Standard Oil, and Du Pontno longer have stakes in the company. (They sold out to a company called Albemarle Paper in1962.) According to McGrayne, as late as February 2001 Ethyl continued to contend “thatresearch has failed to show that leaded gasoline poses a threat to human health or theenvironment.” On its website, a history of the company makes no mention of lead—or indeedof Thomas Midgley—but simply refers to the original product as containing “a certaincombination of chemicals.”
What Patterson found was that before 1923 there was almost no lead in the atmosphere, andthat since that time its level had climbed steadily and dangerously. He now made it his life’squest to get lead taken out of gasoline. To that end, he became a constant and often vocalcritic of the lead industry and its interests.
But there were many technical difficulties to overcome. Holmes also needed—or at leastwould very much have appreciated—sophisticated gadgetry of a sort that could make veryfine measurements from tiny samples, and as we have seen it was all he could do to get asimple adding machine. So it was quite an achievement when in 1946 he was able toannounce with some confidence that the Earth was at least three billion years old and possiblyrather more. Unfortunately, he now met yet another formidable impediment to acceptance: theconservativeness of his fellow scientists. Although happy to praise his methodology, manymaintained that he had found not the age of the Earth but merely the age of the materials fromwhich the Earth had been formed.
Ethyl no longer makes leaded gasoline, although, according to its 2001 company accounts,tetraethyl lead (or TEL as it calls it) still accounted for $25.1 million in sales in 2000 (out ofoverall sales of $795 million), up from $24.1 million in 1999, but down from $117 million in1998. In its report the company stated its determination to “maximize the cash generated byTEL as its usage continues to phase down around the world.” Ethyl markets TEL through anagreement with Associated Octel of England.
Soon afterward, at a meeting in Wisconsin, Patterson announced a definitive age for theEarth of 4,550 million years (plus or minus 70 million years)—“a figure that standsunchanged 50 years later,” as McGrayne admiringly notes. After two hundred years of trying,the Earth finally had an age.
Lead is a neurotoxin. Get too much of it and you can irreparably damage the brain andcentral nervous system. Among the many symptoms associated with overexposure areblindness, insomnia, kidney failure, hearing loss, cancer, palsies, and convulsions. In its mostacute form it produces abrupt and terrifying hallucinations, disturbing to victims andonlookers alike, which generally then give way to coma and death. You really don’t want toget too much lead into your system.
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.
Buoyed by the success of leaded gasoline, Midgley now turned to another technologicalproblem of the age. Refrigerators in the 1920s were often appallingly risky because they useddangerous gases that sometimes leaked. One leak from a refrigerator at a hospital inCleveland, Ohio, in 1929 killed more than a hundred people. Midgley set out to create a gasthat was stable, nonflammable, noncorrosive, and safe to breathe. With an instinct for theregrettable that was almost uncanny, he invented chlorofluorocarbons, or CFCs.
On the other hand, lead was easy to extract and work, and almost embarrassingly profitableto produce industrially—and tetraethyl lead did indubitably stop engines from knocking. So in1923 three of America’s largest corporations, General Motors, Du Pont, and Standard Oil ofNew Jersey, formed a joint enterprise called the Ethyl Gasoline Corporation (later shortenedto simply Ethyl Corporation) with a view to making as much tetraethyl lead as the world waswilling to buy, and that proved to be a very great deal. They called their additive “ethyl”
It would prove to be a hellish campaign. Ethyl was a powerful global corporation withmany friends in high places. (Among its directors have been Supreme Court Justice LewisPowell and Gilbert Grosvenor of the National Geographic Society.) Patterson suddenly foundresearch funding withdrawn or difficult to acquire. The American Petroleum Institutecanceled a research contract with him, as did the United States Public Health Service, asupposedly neutral government institution.
The assumption he made—rather a large one, but correct as it turned out—was that manymeteorites are essentially leftover building materials from the early days of the solar system,and thus have managed to preserve a more or less pristine interior chemistry. Measure the ageof these wandering rocks and you would have the age also (near enough) of the Earth.
Seldom has an industrial product been more swiftly or unfortunately embraced. CFCs wentinto production in the early 1930s and found a thousand applications in everything from carair conditioners to deodorant sprays before it was noticed, half a century later, that they weredevouring the ozone in the stratosphere. As you will be aware, this was not a good thing.
because it sounded friendlier and less toxic than “lead” and introduced it for publicconsumption (in more ways than most people realized) on February 1, 1923.
Even though lead was widely known to be dangerous, by the early years of the twentiethcentury it could be found in all manner of consumer products. Food came in cans sealed withlead solder. Water was often stored in lead-lined tanks. It was sprayed onto fruit as a pesticidein the form of lead arsenate. It even came as part of the packaging of toothpaste tubes. Hardlya product existed that didn’t bring a little lead into consumers’ lives. However, nothing gave ita greater and more lasting intimacy than its addition to gasoline.
The problem with measuring the age of the Earth was that you needed rocks that wereextremely ancient, containing lead- and uranium-bearing crystals that were about as old as theplanet itself—anything much younger would obviously give you misleadingly youthfuldates—but really ancient rocks are only rarely found on Earth. In the late 1940s no onealtogether understood why this should be. Indeed, and rather extraordinarily, we would bewell into the space age before anyone could plausibly account for where all the Earth’s oldrocks went. (The answer was plate tectonics, which we shall of course get to.) Patterson,meantime, was left to try to make sense of things with very limited materials. Eventually, andingeniously, it occurred to him that he could circumvent the rock shortage by using rocksfrom beyond Earth. He turned to meteorites.
Most geology textbooks don’t mention him. Two recent popular books on the history of thedating of Earth actually manage to misspell his name. In early 2001, a reviewer of one ofthese books in the journal Nature made the additional, rather astounding error of thinkingPatterson was a woman.
Libby’s idea was so useful that he would be awarded a Nobel Prize for it in 1960. It wasbased on the realization that all living things have within them an isotope of carbon calledcarbon-14, which begins to decay at a measurable rate the instant they die. Carbon-14 has ahalf-life—that is, the time it takes for half of any sample to disappear1—of about 5,600 years,so by working out how much a given sample of carbon had decayed, Libby could get a goodfix on the age of an object—though only up to a point. After eight half-lives, only 1/256 of theoriginal radioactive carbon remains, which is too little to make a reliable measurement, soradiocarbon dating works only for objects up to forty thousand or so years old.
Patterson quickly established that we had a lot of lead in the atmosphere—still do, in fact,since lead never goes away—and that about 90 percent of it appeared to come fromautomobile exhaust pipes, but he couldn’t prove it. What he needed was a way to comparelead levels in the atmosphere now with the levels that existed before 1923, when tetraethyllead was introduced. It occurred to him that ice cores could provide the answer.
It took Patterson seven years of patient work just to assemble suitable samples for finaltesting. In the spring of 1953 he traveled to the Argonne National Laboratory in Illinois,where he was granted time on a late-model mass spectrograph, a machine capable of detectingand measuring the minute quantities of uranium and lead locked up in ancient crystals. Whenat last he had his results, Patterson was so excited that he drove straight to his boyhood homein Iowa and had his mother check him into a hospital because he thought he was having aheart attack.
Patterson began work on the project in 1948. Compared with Thomas Midgley’s colorfulcontributions to the march of progress, Patterson’s discovery of the age of the Earth feelsmore than a touch anticlimactic. For seven years, first at the University of Chicago and then atthe California Institute of Technology (where he moved in 1952), he worked in a sterile lab,making very precise measurements of the lead/uranium ratios in carefully selected samples ofold rock.
Almost at once production workers began to exhibit the staggered gait and confusedfaculties that mark the recently poisoned. Also almost at once, the Ethyl Corporationembarked on a policy of calm but unyielding denial that would serve it well for decades. AsSharon Bertsch McGrayne notes in her absorbing history of industrial chemistry,Prometheans in the Lab, when employees at one plant developed irreversible delusions, aspokesman blandly informed reporters: “These men probably went insane because theyworked too hard.” Altogether at least fifteen workers died in the early days of production ofleaded gasoline, and untold numbers of others became ill, often violently so; the exactnumbers are unknown because the company nearly always managed to hush up news ofembarrassing leakages, spills, and poisonings. At times, however, suppressing the newsbecame impossible, most notably in 1924 when in a matter of days five production workersdied and thirty-five more were turned into permanent staggering wrecks at a single ill-ventilated facility.
Holmes was heroic as much for the obstacles he overcame as for the results he achieved.
As rumors circulated about the dangers of the new product, ethyl’s ebullient inventor,Thomas Midgley, decided to hold a demonstration for reporters to allay their concerns. As hechatted away about the company’s commitment to safety, he poured tetraethyl lead over hishands, then held a beaker of it to his nose for sixty seconds, claiming all the while that hecould repeat the procedure daily without harm. In fact, Midgley knew only too well the perilsof lead poisoning: he had himself been made seriously ill from overexposure a few monthsearlier and now, except when reassuring journalists, never went near the stuff if he could helpit.
As always, however, nothing was quite as straightforward as such a breezy descriptionmakes it sound. Meteorites are not abundant and meteoritic samples not especially easy to gethold of. Moreover, Brown’s measurement technique proved finicky in the extreme andneeded much refinement. Above all, there was the problem that Patterson’s samples werecontinuously and unaccountably contaminated with large doses of atmospheric lead wheneverthey were exposed to air. It was this that eventually led him to create a sterile laboratory—theworld’s first, according to at least one account.
To his great credit, Patterson never wavered or buckled. Eventually his efforts led to theintroduction of the Clean Air Act of 1970 and finally to the removal from sale of all leadedgasoline in the United States in 1986. Almost immediately lead levels in the blood ofAmericans fell by 80 percent. But because lead is forever, those of us alive today have about625 times more lead in our blood than people did a century ago. The amount of lead in theatmosphere also continues to grow, quite legally, by about a hundred thousand metric tons ayear, mostly from mining, smelting, and industrial activities. The United States also bannedlead in indoor paint, “forty-four years after most of Europe,” as McGrayne notes.
Midgley never knew this because he died long before anyone realized how destructiveCFCs were. His death was itself memorably unusual. After becoming crippled with polio,Midgley invented a contraption involving a series of motorized pulleys that automaticallyraised or turned him in bed. In 1944, he became entangled in the cords as the machine wentinto action and was strangled.
Because of the accumulated shortcomings of carbon-14, scientists devised other methods ofdating ancient materials, among them thermoluminesence, which measures electrons trappedin clays, and electron spin resonance, which involves bombarding a sample withelectromagnetic waves and measuring the vibrations of the electrons. But even the best ofthese could not date anything older than about 200,000 years, and they couldn’t date inorganicmaterials like rocks at all, which is of course what you need if you wish to determine the ageof your planet.
Libby’s method was also based on the assumption that the amount of carbon-14 in theatmosphere, and the rate at which it has been absorbed by living things, has been consistentthroughout history. In fact it hasn’t been. We now know that the volume of atmosphericcarbon-14 varies depending on how well or not Earth’s magnetism is deflecting cosmic rays,and that that can vary significantly over time. This means that some carbon-14 dates are more1If you have ever wondered how the atoms determine which 50 percent will die and which 50 percent willsurvive for the next session, the answer is that the half-life is really just a statistical convenience-a kind ofactuarial table for elemental things. Imagine you had a sample of material with a half-life of 30 seconds. It isntthat every atom in the sample will exist for exactly 30 seconds or 60 seconds or 90 seconds or some other tidilyordained period. Each atom will in fact survive for an entirely random length of time that has nothing to do withmultiples of 30; it might last until two seconds from now or it might oscillate away for years or decades orcenturies to come. No one can say. But what we can say is that for the sample as a whole the rate ofdisappearance will be such that half the atoms will disappear every 30 seconds. Its an average rate, in otherwords, and you can apply it to any large sampling. Someone once worked out, for instance, that dimes have ahalf-life of about 30 years.
It was just at this time that Harrison Brown of the University of Chicago developed a newmethod for counting lead isotopes in igneous rocks (which is to say those that were createdthrough heating, as opposed to the laying down of sediments). Realizing that the work wouldbe exceedingly tedious, he assigned it to young Clair Patterson as his dissertation project.
Finally, and perhaps a little unexpectedly, readings can be thrown out by seeminglyunrelated external factors—such as the diets of those whose bones are being tested. Onerecent case involved the long-running debate over whether syphilis originated in the NewWorld or the Old. Archeologists in Hull, in the north of England, found that monks in amonastery graveyard had suffered from syphilis, but the initial conclusion that the monks haddone so before Columbus’s voyage was cast into doubt by the realization that they had eaten alot of fish, which could make their bones appear to be older than in fact they were. The monksmay well have had syphilis, but how it got to them, and when, remain tantalizinglyunresolved.
His main work done, Patterson now turned his attention to the nagging question of all thatlead in the atmosphere. He was astounded to find that what little was known about the effectsof lead on humans was almost invariably wrong or misleading—and not surprisingly, hediscovered, since for forty years every study of lead’s effects had been funded exclusively bymanufacturers of lead additives.
