10 GETTING THE LEAD OUT

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    IE 1940s, a graduate student at the Uy of Chied Clair Patterson(who was, first withstanding, an Iowa farm boy by in) 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 inated—usually wildly so. Most tained something like twohuimes 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 iorhomas Midgley, Jr.

    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 i in the industrial applications ofchemistry. In 1921, while w for the General Motors Research Corporation in Dayton,Ohio, he iigated a pound called tetraethyl lead (also known, fusingly, as leadtetraethyl), and discovered that it signifitly reduced the juddering dition known asengine knock.

    Even though lead was widely known to be dangerous, by the early years of the twehtury it could be found in all manner of er products. Food came in s sealed withlead solder. Water was often stored in lead-lianks. It rayed onto fruit as a pesticidein the form of lead arse even came as part of the packaging of toothpaste tubes. Hardlya product existed that didn’t bring a little lead into ers’ lives. However, nothing gave ita greater and more lasting intimacy than its addition to gasoline.

    Lead is a oxioo much of it and you  irreparably damage the brain aral nervous system. Among the many symptoms associated with overexposure areblindness, insomnia, kidney failure, hearing loss, cer, palsies, and vulsions. In its mostacute form it produces abrupt and terrifying halluations, disturbing to victims andonlookers alike, which generally then give way to a ah. You really don’t want toget too much lead into your system.

    Oher hand, lead was easy to extrad work, and almost embarrassingly profitableto produdustrially—araethyl lead did indubitably stop engines from knog. So in1923 three of America’s largest corporations, General Motors, Du Pont, and Standard Oil ofNew Jersey, formed a joierprise called the Ethyl Gasoline Corporation (later shorteo 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”

    because it sounded friendlier aoxic than “lead” and introduced it for publiption (in more ways than most people realized) on February 1, 1923.

    Almost at once produ workers began to exhibit the staggered gait and fusedfaculties that mark the retly poisoned. Also almost at ohe Ethyl Corporationembarked on a policy of calm but unyielding denial that would serve it well for decades. AsSharosch McGrayes in her abs 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 produ ofleaded gasoline, and untold numbers of others became ill, often violently so; the exaumbers are unknown because the pany nearly always mao 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 produ workersdied and thirty-five more were turned into perma staggering wrecks at a single ill-ventilated facility.

    As rumors circulated about the dangers of the new product, ethyl’s ebullient ior,Thomas Midgley, decided to hold a demonstration for reporters to allay their s. As hechatted away about the pany’s itment to safety, he poured tetraethyl lead over hishands, then held a beaker of it to his nose for sixty seds, 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 overex<cite>藏书网</cite>posure a few monthsearlier and now, except when reassuring journalists, never wehe stuff if he could helpit.

    Buoyed by the success of leaded gasoline, Midgley now turo aeologicalproblem 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 uny, he ied chlorofluorocarbons, or CFCs.

    Seldom has an industrial product been more swiftly or unfortunately embraced. CFCs wentinto produ in the early 1930s and found a thousand applications ihing from carair ditioo deodorant sprays before it was noticed, half a tury later, that they weredev the ozone iratosphere. As you will be aware, this was not a good thing.

    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  iratosphere it is beneficial, si soaks up dangerous ultraviolet radiation. Beneficial ozoneis not terribly abundant, however. If it were distributed evenly throughout the stratosphere, itwould form a layer just oh of an inch or so thick. That is why it is so easily disturbed,and why such disturbances don’t take long to bee critical.

    Chlorofluorocarbons are also not very abundant—they stitute only about one part perbillion of the atmosphere as a whole—but they are extravagantly destructive. One pound ofCFCs  capture and annihilate seventy thousand pounds of atmospheric ozone. CFCs alsohang around for a long time—about a tury on average—wreaking havoc all the while.

    They are also great heat sponges. A single CFC molecule is about ten thousand times moreeffit at exacerbating greenhouse effects than a molecule of carbon dioxide—and carbondioxide is of course no slouch itself as a greenhouse gas. In short, chlorofluoroayultimately prove to be just about the worst iion of the tweh tury.

    Midgley never khis because he died long before anyone realized how destructiveCFCs were. His death was itself memorably unusual. After being crippled with polio,Midgley ied a traption involving a series of motorized pulleys that automaticallyraised or turned him in bed. In 1944, he became entangled in the cords as the mae wentinto a and was strangled<var>..</var>.

    If you were ied in finding out the ages of things, the Uy of Chicago in the1940s was the place to be. Willard Libby was in the process of iing radiocarbon dating,allowing stists to get an accurate reading of the age of bones and anic remains,something they had never been able to do before. Up to this time, the oldest reliable dateswent bao further than the First Dynasty i from about 3000B.o one couldfidently say, for instance, when the last ice sheets had retreated or at what time in the pastthe agnon people had decorated the caves of Lascaux in France.

    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 w 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 theinal 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.

    Curiously, just as the teique was being widespread, certain flaws within it becameapparent. To begin with, it was discovered that one of the basipos of Libby’sformula, known as the decay stant, was off by about 3 pert. By this time, however,thousands of measurements had been taken throughout the world. Rather thae everyone, stists decided to keep the inaccurate stant. “Thus,” Tim Flannery notes, “everyraw radiocarbon date you read today is given as too young by around 3 pert.” Theproblems didn’t quite stop there. It was also quickly discovered that carbon-14 samples  beeasily inated with carbon from other sources—a tiny scrap of vegetable matter, forinstahat has been collected with the sample and not noticed. For younger samples—those uwenty thousand years or so—slight ination does not always matter somuch, but for older samples it  be a serious problem because so few remaining atoms arebeing ted. In the first instao borrow from Flannery, it is like misting by a dollarwhen ting to a thousand; in the sed it is more like misting by a dollar when youhave only two dollars to t.

    Libby’s method was also based on the assumption that the amount of carbon-14 imosphere, and the rate at which it has been absorbed by living things, has been sistentthroughout history. In fact it hasn’t been. We now know that the volume of atmosphericcarbon-14 varies depending on how well or h’s magism is defleg ic rays,and that that  vary signifitly over time. This means that some carbon-14 dates are more1If you have ever wondered how the atoms determine which 50 pert will die and which 50 pert willsurvive for the  session, the answer is that the half-life is really just a statistical venience-a kind ofactuarial table for elemental things. Imagine you had a sample of material with a half-life of 30 seds. It isntthat every atom in the sample will exist for exactly 30 seds or 60 seds or 90 seds or some other tidilyordained period. Each atom will in fact survive for airely random length of time that has nothing to do withmultiples of 30; it might last until two seds from now or it might oscillate away for years or decades orturies to e. No one  say. But what we  say is that for the sample as a whole the rate ofdisappearance will be such that half the atoms will disappear every 30 seds. Its an average rate, in otherwords, and you  apply it to any large sampling. Someone once worked out, for instahat dimes have ahalf-life of about 30 years.

    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.

    Finally, and perhaps a little uedly, readings  be thrown out by seeminglyued external factors—such as the diets of those whose bones are beied. O case involved the long-runnie over whether syphilis inated 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 clusion that the monks haddo<tt></tt>ne so before bus’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.

    Because of the accumulated shortings of carbon-14, stists devised other methods ofdating a materials, among them thermoluminesence, which measures eles trappedin clays, aron spin resonance, whivolves b a sample witheleagic waves and measuring the vibrations of the eles. But even the best ofthese could not date anything older than about 200,000 years, and they couldn’t date inanicmaterials like rocks at all, which is of course what you need if you wish to determihe ageof your pla.

    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 abeyaogether.

    Holmes was heroic as much for the obstacles he overcame as for the results he achieved.

    By the 1920s, when Holmes was in the prime of his career, geology had slipped out offashion—physics was the ement of the age—and had bee severely underfunded,particularly in Britain, its spiritual birthplace. At Durham Uy, Holmes was for manyyears the entire geology department. Often he had to borrow or patch together equipment io pursue his radiometric dating of rocks. At one point, his calculations were effectivelyheld up for a year while he waited for the uy to provide him with a simple addingmae. 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.

    The teique Holmes used in his work was theoretically straightforward and arose directlyfrom the process, first observed by Er Rutherford in 1904, in whie atoms decayfrom one element into a a rate predictable enough that you  use them as clocks. Ifyou know how long it takes for potassium-40 to bee argon-40, and you measure theamounts of ea a sample, you  work out how old a material is. Holmes’s tributionwas to measure the decay rate of uranium into lead to calculate the age of rocks, and thus—hehoped—of the Earth.

    But there were many teical difficulties to overe. 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 mae. So it was quite an achievement when in 1946 he was able toannouh some fidehat the Earth was at least three billion years old and possiblyrather more. Unfortunately, he now met yet another formidable impediment to acceptaheservativeness of his fellow stists. Although happy to praise his methodology, manymaintaihat he had found not the age of the Earth but merely the age of the materials fromwhich the Earth had been formed.

    It was just at this time that Harrison Brown of the Uy of Chicago developed a hod for ting 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 assig to young Clair Patterson as his dissertation project.

    Famously he promised Patterson that determining the age of the Earth with his new methodwould be “duck soup.” In fact, it would take years.

    Patterson began work on the proje 1948. pared with Thomas Midgley’s colorfultributions to the march ress, Patterson’s discovery of the age of the Earth feelsmore than a touticlimactic. For seven years, first at the Uy of Chicago and then atthe California Institute of Teology (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.

    The problem with measuring the age of the Earth was that you needed rocks that wereextremely a, taining lead- and uranium-bearing crystals that were about as old as theplaself—anything much younger would obviously give you misleadingly youthfuldates—but really a rocks are only rarely found oh. Ie 1940s no oogether uood why this should be. Indeed, and rather extraordinarily, we would bewell into the space age before anyone could plausibly at for where all the Earth’s oldrocks went. (The answer late teics, which we shall of cet to.) Pattersoime, was left to try to make sense of things with very limited materials. Eventually, adingeniously, it occurred to him that he could circumvent the rock she by using rocksfrom beyoh. He turo meteorites.

    The assumption he made—rather a large one, but correct as it turned out—was that maeorites are essentially leftover building materials from the early days of the solar system,and thus have mao preserve a more or less pristierior chemistry. Measure the ageof these wandering rocks and you would have the age also (near enough) of the Earth.

    As always, however, nothing was quite as straightforward as such a breezy descriptio sound. Meteorites are not abundant aeoritic samples not especially easy to gethold of. Moreover, Brown’s measurement teique proved finicky ireme andneeded much refi. Above all, there was the problem that Patterson’s samples weretinuously and unatably inated with large doses of atmospheric lead whehey were exposed to air. It was this that eventually led him to create a sterile laboratory—theworld’s first, acc to at least one at.

    It took Patterson seven years of patient work just to assemble suitable samples for fiing. In the spring of 1953 he traveled to the Argoional Laboratory in Illinois,where he was graime on a late-model mass spectrograph, a mae capable of detegand measuring the minute quantities of uranium and lead locked up in a 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.

    Soon afterward, at a meeting in Wissin, Patterson announced a definitive age for theEarth of 4,550 million years (plus or minus 70 million years)—“a figure that standsunged 50 years later,” as McGrayne admiringly notes. After two hundred years ,the Earth finally had an age.

    His main work done, Patterson now turned his attention to the nagging question of all thatlead imosphere. He was astouo 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.

    In one such study, a doctor who had no specialized training in chemical pathologyuook a five-year program in which volunteers were asked to breathe in or swallow leadied 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—aher bone nor blood wastested. In sequence, lead was given a  bill of <q>?</q>health.

    Patterson quickly established that we had a lot of lead imosphere—still do, in fact,since lead never goes away—and that about 90 pert of it appeared to e fromautomobile exhaust pipes, but he couldn’t prove it. What he needed was a way to parelead levels imosphere now with the levels that existed before 1923, wheraethyllead was introduced. It occurred to him that ice cores could provide the answer.

    It was known that snowfall in places like Greenland accumulates into discrete annual layers(because seasonal temperature differences produce slight ges in coloration from wiosummer). By ting back through these layers and measuring the amount of lead in each, hecould work out global lead trations 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.

    atterson found was that before 1923 there was almost no lead imosphere, andthat sihat time its level had climbed steadily and dangerously. He now made it his life’squest to get lead taken out of gasolio that end, he became a stant and often vocalcritic of the lead industry and its is.

    It would prove to be a hellish campaighyl owerful 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 Ameri Petroleum Instituteceled a research tract with him, as did the Uates Public Health Service, asupposedly ral gover institution.

    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. Acc to JamieLin Kitman, writing iion in 2000, Ethyl executives allegedly offered to endow achair at Caltech “if Patterson was sent pag.” Absurdly, he was excluded from a 1971National Research cil panel appoio iigate the dangers of atmospheric leadpoisoning even though he was by now uionably the leading expert on atmospheric lead.

    To his great credit, Patterson never wavered or buckled. Eventually his efforts led to theintrodu of the  Air Act of 1970 and finally to the removal from sale of all leadedgasoline in the Uates in 1986. Almost immediately lead levels in the blood ofAmeris fell by 80 pert. But because lead is forever, those of us alive today have about625 times more lead in our blood than people did a tury ago. The amount of lead imosphere also tio grow, quite legally, by about a huhousaris ayear, mostly from mining, smelting, and industrial activities. The Uates also bannedlead in indoor paint, “forty-four years after most of Europe,” as McGrayes.

    Remarkably, sidering its startling toxicity, lead solder was not removed from Amerifood tainers until 1993.

    As for the Ethyl Corporation, it’s still going strong, though GM, Standard Oil, and Du Pontno longer have stakes in the pany. (They sold out to a pany called Albemarle Paper in1962.) Acc to McGrayne, as late as February 2001 Ethyl tio tend “thatresearch has failed to show that leaded gasoline poses a threat to humah or theenviro.” On its website, a history of the pany makes ion of lead—or indeedof Thomas Midgley—but simply refers to the inal product as taining “a certainbination of chemicals.”

    Ethyl no longer makes leaded gasoline, although, acc to its 2001 pany ats,tetraethyl lead (or TEL as it calls it) still ated 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 pany stated its determination to “maximize the cash geed byTEL as its usage tio phase down around the world.” Ethyl markets TEL through anagreement with Associated Octel of England.

    As for the other sce left to us by Thomas Midgley, chlorofluorocarbons, they werebanned in 1974 in the Uates, 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 dev ozone long after you have shuffled off. Worse, weare still introdug huge amounts of CFto the atmosphere every year. Acc 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 Worldtries until 2010.

    Clair Patterson died in 1995. He didn’t win a Nobel Prize for his weologists neverdo. Nor, more puzzlingly, did he gain any fame or even much attention from half a tury ofsistent and increasingly selfless achievement. A good case could be made that he was themost iial geologist of the tweh tury. Yet who has ever heard of Clair Patterson?

    Most geology textbooks don’t mention him. Two ret popular books on the history of thedating of Earth actually mao misspell his name. In early 2001, a reviewer of ohese books in the journal Nature made the additional, rather astounding error of thinkingPatterson was a woman.

    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 thattai.

百度搜索 A Short History of Nearly Everything 天涯 或 A Short History of Nearly Everything 天涯在线书库 即可找到本书最新章节.