万物简史英文版_比尔·布莱森-第29章

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ttle　lead　into　consumers鈥櫋�lives。　however；　nothing　gave　ita　greater　and　more　lasting　intimacy　than　its　addition　to　gasoline。

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　a　and　death。　you　really　don鈥檛　want　toget　too　much　lead　into　your　system。

on　the　other　hand；　lead　was　easy　to　extract　and　work；　and　almost　embarrassingly　profitableto　produce　industrially鈥攁nd　tetraethyl　lead　did　indubitably　stop　engines　from　knocking。　so　in1923　three　of　america鈥檚　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　鈥渆thyl鈥�

because　it　sounded　friendlier　and　less　toxic　than　鈥渓ead鈥潯�and　introduced　it　for　publicconsumption　（in　more　ways　than　most　people　realized）　on　february　1；　1923。

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；　aspokesman　blandly　informed　reporters：　鈥渢hese　men　probably　went　insane　because　theyworked　too　hard。鈥潯�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　pany　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。

as　rumors　circulated　about　the　dangers　of　the　new　product；　ethyl鈥檚　ebullient　inventor；thomas　midgley；　decided　to　hold　a　demonstration　for　reporters　to　allay　their　concerns。　as　hechatted　away　about　the　pany鈥檚　mitment　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。

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。

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。

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鈥檛　take　long　to　bee　critical。

chlorofluorocarbons　are　also　not　very　abundant鈥攖hey　constitute　only　about　one　part　perbillion　of　the　atmosphere　as　a　whole鈥攂ut　they　are　extravagantly　destructive。　one　pound　ofcfcs　can　capture　and　annihilate　seventy　thousand　pounds　of　atmospheric　ozone。　cfcs　alsohang　around　for　a　long　time鈥攁bout　a　century　on　average鈥攚reaking　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鈥攁nd　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。

midgley　never　knew　this　because　he　died　long　before　anyone　realized　how　destructivecfcs　were。　his　death　was　itself　memorably　unusual。　after　being　crippled　with　polio；midgley　invented　a　contraption　involving　a　series　of　motorized　pulleys　that　automaticallyraised　or　turned　him　in　bed。　in　1944；　he　became　entangled　in　the　cords　as　the　machine　wentinto　action　and　was　strangled。

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。

libby鈥檚　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鈥攖hat　is；　the　time　it　takes　for　half　of　any　sample　to　disappear1鈥攐f　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鈥攖hough　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。

curiously；　just　as　the　technique　was　being　widespread；　certain　flaws　within　it　becameapparent。　to　begin　with；　it　was　discovered　that　one　of　the　basic　ponents　of　libby鈥檚formula；　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。　鈥渢hus；鈥潯�tim　flannery　notes；　鈥渆veryraw　radiocarbon　date　you　read　today　is　given　as　too　young　by　around　3　percent。鈥潯�theproblems　didn鈥檛　quite　stop　there。　it　was　also　quickly　discovered　that　carbon…14　samples　can　beeasily　contaminated　with　carbon　from　other　sources鈥攁　tiny　scrap　of　vegetable　matter；　forinstance；　that　has　been　collected　with　the　sample　and　not　noticed。　for　younger　samples鈥攖hose　under　twenty　thousand　years　or　so鈥攕light　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。

libby鈥檚　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鈥檛　been。　we　now　know　that　the　volume　of　atmosphericcarbon…14　varies　depending　on　how　well　or　not　earth鈥檚　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　e。　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。

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　unexpectedly；　readings　can　be　thrown　out　by　seeminglyunrelated　external　factors鈥攕uch　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鈥檚　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；　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鈥檛　date　inorganicmaterials　like　rocks　at　all；　which　is　of　course　what　you　need　if　you　wish　to　determine　the　ageof　your　planet。

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。

holmes　was　heroic　as　much　for　the　obstacles　he　overcame　as　for　the　results　he　achieved。

by　the　19