,nucle> ,clocks ,! ,und]/&+ ! ,atom ,s]ies ,nucle> ,en]gy is play+ a vital role 9 ! life ( e man1 woman1 & *ild 9 ! ,unit$ ,/ates today4 ,9 ! ye>s ahead x w affect increas+ly all ! peoples ( ! e>?4 ,x is ess5tial t all ,am]icans ga9 an und]/&+ ( ?is vital =ce if !y are to dis*>ge ?\ghtfully _! responsibilities z citiz5s & if !y are to realize fully ! myriad b5efits t nucle> en]gy (f]s !m4 ,! ,unit$ ,/ates ,atomic ,en]gy ,commission provides ?is booklet to help y a*ieve su* und]/&+4 ,illu/ration3 ,signature ( ,edw>d ,j4 ,brun5kant ,edw>d ,j4 ,brun5kant1 ,director ,division ( ,te*nical ,in=mation ,,unit$ ,,/ates ,,atomic ,,en]gy ,,commission ,dr4 ,gl5n ,t4 ,seaborg1 ,*airman ,james ,t4 ,ramey ,wilfrid ,e4 ,johnson ,francesco ,co/agliola ,illu/ration3 ,,nucle> ,,clocks by ,h5ry ,faul ,,cont5ts ,,introduction #a ,,!ory ,,( ,,nucle> ,,age ,,det]m9ation #e ,,! ,,c>bon-#ad ,,clock #i ,c>bon-#ad ,c\nt+ #ab ,c>bon-#ad ,results #ae ,,! ,,long-,,liv$ ,,clocks #ai ,! ,rubidium-,/rontium ,clock #bj ,! ,uranium ,fission ,clock #bd ,plumbology #bg ,,! ,,age ,,( ,,! ,,e>? #bg ,analytical ,te*niques #ca ,m9]als ,t ,c ,be ,dat$ #cd ,,"s ,,int]e/+ ,,results #dj ,! ,old ,man ,f ,olduvai #dj ,! ,geologic ,"t ,scale #da ,precambrian ,/ratigraphy #dg ,,& ,,:]e ,,d ,,we ,,g ,,f ,,"h8 #dh ,,gloss>y #di ,,app5dix #eb ,,sugge/$ ,,ref]5ces #eh ,unit$ ,/ates ,atomic ,en]gy ,commission ,division ( ,te*nical ,in=mation ,libr>y ( ,congress ,catalog ,c>d ,numb]3 #fg-fjaie #aiff2 #aifh7,rev47 ,illu/ration3 ,a #ad1jjj-ye>-old burial site be+ uncov]$ 9 ! area ( ! ,aswan ,res]voir 9 ,sudan4 ,to det]m9e ! age ( su* anci5t rema9s1 ar*aeologi/s se>* = e scrap ( associat$ wood or *>coal t c\ld be us$ = age measurem5t ( c>bon-#ad1 "o ( ! 8nucle> clocks0 describ$ 9 ?is booklet4 ,illu/ration3 ,,nucle> ,,clocks ,by ,,h5ry ,,faul ,,introduction ,h[ old is a rock8 ,h[ old is man8 ,h[ old is ! e>?8 ,x w\ld be difficult to f9d a reason :y anyone w\ld really h to "k ! answ]s to ^! que/ions1 yet !y h be5 ask$ ov] & ov] aga9 s9ce ! dawn ( human society4 ,! records ( e civilization disclose attempts to delve into ! pa/ beyond ! memory ( ! olde/ man1 beyond record$ hi/ory1 beyond e>lie/ leg5d4 ,curiosity ab\t ! remote pa/ may be v anci5t1 b ! only reliable me?od ( measur+ v long int]vals ( "t is new4 ,! possibility ( do+ s became app>5t only aft] ! discov]y ( ,,radioactivity#a 9 #ahif by ,h5ri ,becqu]el1 :5 ,m>ie & ,pi]re ,curie 9 #ahih recogniz$ t "s atoms are radioactive & *ange by !mselves into o!r atoms at regul> & con/ant rates4 ,if some?+ gradually trans=ms itself into some?+ else1 if ?is trans=mation goes on at a kn[n pace1 & if all ! products ( ! activity are pres]v$ 9 "s k9d ( a ,,clos$ ,,sy/em1 !n x is !oretically possible to calculate ! "t t has elaps$ s9ce ! process />t$4 ,! !ory 0 cle> = ye>s2 ! only problem 0 h[ to satisfy all ^? ifs4 ,by #aiaj x 0 well e/abli%$ t ! e>? mu/ be extremely anci5t4 ,analyses ( "s m9]als conta9+ uranium %[$ !m to be hundr$s ( millions ( ye>s old1 ev5 ?\gh ! uranium came f rocks t 7 kn[n to be relatively "y among geologic ,,/rata4 ,measurem5ts /ill 7 inaccurate1 h[ev]1 & only a few r>e & unusually ri* radioactive m9]als conta9$ en\gh ( ! products ( ,,radioactive ,,decay#b to all[ analysis ( _! age by ! crude me?ods !n available4 ,n mu* progress 0 made = ab\t #cj ye>s until ,a4 ,o4 ,c4 ,ni]1 a ,h>v>d ,univ]sity physici/1 p]fect$ an in/rum5t call$ a ,,mass ,,spectromet] 7to be describ$ lat]7 j be=e ,_w ,w> ,,ii4 ,! rapid te*nological advances ( ! w> ye>s foll[$4 ,! ,manhattan ,project#c made ! atomic bombs t end$ ! fight+2 x also develop$ new sci5tific te*niques t c\ld be appli$1 :5 peace return$1 to ! measurem5t ( geologic "t4 ,! next important advance 0 contribut$ 9 #aidf by ,ar?ur ,holmes 9 ,engl& & by ,f4 ,g4 ,h\t]mans 9 ,g]many4 ,ea* ( ^! sci5ti/s _h se5 ,ni]'s reports be=e ! w> & _h realiz$ t ,ni]'s mass-spectromet] analyses ( lead made x possible1 = ! fir/ "t1 to make rational calculations ab\t ! age ( ! e>?4 ,! two sci5ti/s indep5d5tly calculat$ t age at ab\t #b to #c billion ye>s1 us+ ! h&ful ( data available to !m f ,ni]'s measurem5ts4 ,x is int]e/+ t today1 ?\s&s ( analyses lat]1 our planet's age usually is giv5 z #d4e billion ye>s4 ,! e>ly e/imates 7 n f> (f4 ,developm5t ( v>i\s me?ods = measur+ ! age ( m9]als foll[$ rapidly1 & by #aiee _m fundam5tal /udies ne$$ = measur+ ! age ( v old sub/ances 7 complete4 ,! basic te*niques are summ>iz$ 9 ,table ,i4 ,!y w be expla9$ lat]4 ,! new me?ods produc$ broad confirmation ( ! e>ly r\gh e/imates & !y also br\ght a few surprises4 ,be=e we g into ^! discov]ies1 let u look at "s !oretical f\ndations4 ,table ,i ,,basic ,,measurem5t ,,me?ods ,me?od ,mat]ial ,"t ,dat$ ,useful ,"t ,span 7ye>s7 ,c>bon-#ad ,wood1 peat1 ,:5 plant di$ #ajjj-ej1jjj *>coal ,bone1 %ell ,slightly be=e #bjjj-ce1jjj animal di$ ,potassium-argon ,mica1 "s ,:5 rock la/ #ajj1jjj & up :ole rocks cool$ to ab\t #cjj;,c ,hornbl5de ,:5 rock la/ #aj1jjj1jjj & up ,sanid9e cool$ to ab\t #ejj;,c ,rubidium-/rontium ,mica ,:5 rock la/ #e1jjj1jjj & up cool$ to ab\t #cjj;,c ,pota% ,:5 rock la/ #ej1jjj1jjj & up feldsp> cool$ to ab\t #ejj;,c ,:ole rock ,"t ( #ajj1jjj1jjj & up sep>ation ( ! rock z a clos$ unit ,uranium-lead ,zircon ,:5 cry/als #bjj1jjj1jjj & up =m$ ,uranium-#bch ,_m ,:5 rock la/ #ajj-a1jjj1jjj1jjj fission cool$ 7,dep5d+ on mat]ial7 ,illu/ration3 ,"t scale ( ! ,e>?1 drawn to scale4 ,see also ! ,holmes "t scale on page #df4 ,ev5t ,geologic ,"t ,p]iod ,era ,man appe>s#d 7#b million ye>s ago7 ,quat]n>y ,,c5ozoic ,t]ti>y ,ext9ction ( ! d9osaurs 7#gj million ye>s ago7 ,cretace\s ,,mesozoic ,mammals appe> 7#acj million ye>s ago7 ,jurassic ,triassic ,olde/ kn[n reptiles 7#cjj million ye>s ,p]mian ,,paleozoic ago7 ,p5nsylvanian ,mississippian ,devonian ,silurian ,ordovician ,cambrian ,fir/ abundant life 9 ! sea 7animals )\t backbones7 7#eej million ye>s ago7 ,algae & o!r microorganisms 7#a1ijj ,prot]ozoic ,,precambrian million ye>s ago7 ,ar*ean ,olde/ rocks 9 ,nor? ,am]ica 7#b1hjj million ye>s ago7 ,fir/ h9t ( life 7bact]ia87 7#c1ajj million ye>s ago7 ,olde/ rocks 7#c1cjj million ye>s old7 ,=mation ( ,e>?'s core 7#d1ejj million ye>s ago7 ,,!ory ,,( ,,nucle> ,,age ,,det]m9ation ,we c ?9k ( ! nucleus ( an atom z a sort ( drop--a bun* ( ,,neutrons & ,,protons held toge!r by v /rong %ort-range =ces4 ,^! elem5t>y p>ticles )9 a nucleus are n arrang$ 9 any fix$ or rigid array1 b are free to move ab\t )9 ! grip ( ^! =ces4 ,^! motions may be q viol5t1 b = mo/ ,,nuclides f\nd 9 nature1 ! nucle> =ces are p[]ful en\gh to keep ev]y?+ conf9$2 ?us ! nuclei ( ^! atoms hold toge!r1 & are said to be /able4 ,if any "o nucleus ( a giv5 ,,isotope is /able1 !n all o!rs are also /able1 because :at is true = "o atom ( a giv5 k9d is true = all o!rs ( ! same k9d4#e ,"s nuclides1 bo? man-made & natural1 are un/able1 h[ev]4 ,_! nuclei are 9 su* viol5t turmoil t ! nucle> =ces _c always hold !m toge!r1 & v>i\s bits & pieces fly (f4 ,if we 7 to try to pr$ict :5 "o p>ticul> un/able nucleus w\ld ?us dis9tegrate1 h[ev]1 we c\ld n succe$1 because ! in/ant any specific decay 7or dis9tegration7 ev5t w occur is a matt] ( *ance4 ,only if a l>ge numb] ( un/able nuclei ( "o k9d are collect$ toge!r c we say ) c]ta9ty t1 out ( t numb]1 a c]ta9 proportion w decay 9 a giv5 "t4 ,x turns out t ?is proportion is ! same reg>dless ( any ext]nal conditions4 ,?is prop]ty ( nuclei to decay by !mselves is call$ radioactivity4 ,radioactive nuclei decay at con/ant rates reg>dless ( temp]ature1 pressure1 *emical comb9ation1 or physical /ate4 ,! process goes on no matt] :at happ5s to ! atom4 ,9 o!r words1 ! activity inside ! nucleus is 9 no way affect$ by :at happ5s to ! ,,electrons circl+ ar\nd x4 7,only 9 v special cases c outside di/urbances affect ! radioactivity ( a nucleus & !n only slightly4 ,= all practical purposes1 rates ( radioactive decay are con/ant47 ,mo/ radioactive nuclides h rapid rates ( decay 7& lose _! radioactivity 9 a few days1 or a few ye>s1 at mo/72 mo/ ( ^! are kn[n today only because !y are produc$ artificially4 ,"s ( !m may h be5 pres5t at ! "t ! sol> sy/em 0 =m$1 b !y h s9ce decay$ to su* insignificant fractions ( _! orig9al am\nts t !y c no long] be detect$4 ,only a few radioactive nuclides decay sl[ly en\gh to h be5 pres]v$ to ?is day1 & s are pres5t 9 nature4 ,!y are li/$ 9 ,table ,,ii4 ,table ,,ii ,,radioactive ,,nuclides ,,) ,,half-,,lives ,,l>ge ,,en\gh ,,to ,,be ,,/ill ,,pres5t ,,9 ,,useful ,,am\nts ,,on ,,! ,,e>?#f ,,p>5t ,elem5t ,,daught] ,,half-,,life 7ye>s7 ,type ( ,decay ,product ,potassium-#dj ,argon-#dj #a4c #aj 7total7 ,,electron ,,capture ,calcium-#dj ,,beta ,,decay ,vanadium-#ej ,titanium-#ej #f #aj 7total7 ,electron capture ,*romium-#ej ,beta decay ,rubidium-#hg ,/rontium-#hg #d4g #aj ,beta decay ,indium-#aae ,t9-#aae #e #aj ,beta decay ,tellurium-#abc ,antimony-#abc #a4b #aj ,electron capture ,lan?anum-#ach ,b>ium-#ach #a4a #aj 7total7 ,electron capture ,c]ium-#ach ,beta decay ,c]ium-#adb ,b>ium-#ach #e #aj ,,alpha ,,decay ,neodymium-#add ,c]ium-#adj #b4d #aj ,alpha decay ,sam>ium-#adg ,neodymium-#adc #a4jf #aj ,alpha decay ,sam>ium-#adh ,neodymium-#add #a4b #aj ,alpha decay ,sam>ium-#adi ,neodymium-#ade #d #aj8 ,alpha decay ,gadol9ium-#aeb ,sam>ium-#adh #a4a #aj ,alpha decay ,dysprosium-#aef ,gadol9ium-#aeb #b #aj ,alpha decay ,hafnium-#agd ,ytt]bium-#agj #d4c #aj ,alpha decay ,lutetium-#agf ,hafnium-#agf #b4b #aj ,beta decay ,rh5ium-#ahg ,osmium-#ahg #d #aj ,beta decay ,plat9um-#aij ,osmium-#ahf #g #aj ,alpha decay ,lead-#bjd ,m]cury-#bjj #a4d #aj ,alpha decay ,?orium-#bcb ,lead-#bjh #a4da #aj #f ,alpha #d beta#g ,uranium-#bce ,lead-#bjg #g4ac #aj #g ,alpha #d beta ,uranium-#bch ,lead-#bjf #d4ea #aj #h ,alpha #f beta ,9 a l>ge numb] ( radioactive nuclei ( a giv5 k9d1 a c]ta9 fraction w decay 9 a specific l5g? ( "t4 ,let's take ?is fraction z "o-half & measure ! "t x takes = half ! nuclei to decay4 ,?is "t x is call$ ! ,,half-,,life ( t p>ticul> nucleus & !re are v>i\s accurate physical ways ( measur+ x4 ,dur+ ! int]val ( "o half-life1 "o-half ( ! nuclei w decay1 dur+ ! next half-life half ( :at's left w decay1 & s on4 ,we may tabulate x l ?is3 ,elaps$ "t ,am\nt left ( 7,numb] ( :at 0 half-lives7 orig9ally pres5t #a #b #c #d _/ #e _/ #f _/ #g _/ 444 444 ,9 o!r words1 aft] sev5 half-lives1 less ?an #a ( ! orig9al am\nt ( mat]ial w /ill be radioactive & ! rema9+ #ii ( its atoms w h be5 conv]t$ to atoms ( ano!r nuclide4 ,?is k9d ( process c be made ! basis ( a clock4 ,x works1 9 effect1 l ! upp] *amb] ( an h\rglass4 ,ma!matically x is writt53 ,n ,ne-t :]e ,n ! numb] ( radioactive atoms pres5t 9 ! sy/em n[1 ,n ! numb] t 0 pres5t :5 t #j1 79 o!r words1 at ! "t ! clock />t$71 e ! base ( natural 7or ,napi]ian#h7 log>i?ms 7! num]ical value ( e #b4gah 44471 7lambda7 ! decay rate ( ! radioactive mat]ial1 express$ 9 atoms decay+ p] atom p] unit ( "t1 t ! "t t has elaps$ s9ce ! orig9 ( sy/em1 express$ 9 ! same units4 ,obvi\sly1 9 ord9>y computations t w\ld n be en\gh in=mation to calculate ! "t1 because !re /ill are two unkn[ns1 ,n & t4 ,9 a clos$ sy/em1 h[ev]1 ! atoms t h decay$ d n disappe> into ?9 air4 ,!y m]ely *ange into o!r atoms1 call$ daught] atoms1 & rema9 9 ! sy/em4 ,& at any po9t 9 "t1 !re w be bo? ,,p>5t & ,,daught] atoms mix$ toge!r 9 ! mat]ial4 ,! old] ! mat]ial1 ! m daught]s & ! few] p>5ts4 ,"s daught]s are also radioactive1 b ?is does n *ange ! basic situation4 ,?us x foll[s t ,n ,n ,d :]e ,d ! numb] ( daught] 7decay$7 atoms4 ,we may !n sub/itute into ! fir/ equation ,n 7,n ,d7 e-t & solve t #a_/ ln7#a ,d_/,n7 :]e ln ! natural log>i?m1 ! log>i?m to base e4 ,?is k9d ( sy/em c be repres5t$ crudely by an old-fa%ion$ h\rglass1 z %[n 9 ! figure1 :i* has ! p>amet]s ( ^! equations m>k$4 7,keep 9 m9d1 h[ev]1 t ?is is only a gross analogy4 ,nucle> clocks run at log>i?mically decreas+ rates1 b ! spe$ ( a good h\rglass is r\ghly con/ant47 ,illu/ration3 ,an h\rglass illu/rates an ideal clos$ sy/em4 ,no?+ is add$ & no?+ is remov$--! s& j runs f ! top bulb to ! bottom4 ,rememb] t ! decay+ nucleus does n disappe>4 ,x *anges into ano!r nucleus1 & ?is new nucleus =ms an atom t may be captur$ & held fix$ by natural processes4 ,! decay$ nuclei are ?us collect$1 s t "h we h ! bottom *amb] ( ! h\rglass4 ,b sometimes we ne$ only ! top *amb] ( an h\rglass4 ,,! ,,c>bon-#ad ,,clock ,c>bon-#ad decay is ! be/ example ( a top-only h\rglass4 ,c>bon-#ad is con/antly be+ produc$ 9 ! upp] atmosph]e f atoms ( nitrog5-#ad be+ /ruck by neutrons t _h _! orig9 9 ,,cosmic ,,rays4 ,! reaction is writt53 ,n neutron ,c proton ,radioactive decay !n foll[s1 ) a half-life ( #ehjj ye>s#i = ! ,c4 ,c ,n electron 7,,beta ,,p>ticle7 ,! radioc>bon emits an electron & *anges back into nitrog54 ,z f> z anyone c tell1 ,c 0 produc$ at a con/ant rate above ! e>? = at lea/ #ej1jjj ye>s be=e ! fir/ atomic bomb 0 explod$4 ,9 o!r words1 ! ,c cycle is l an h\rglass 9 :i* ! s& 9 ! upp] "p is repl5i%$ z fa/ z x runs out ?r\gh ! hole 9 ! wai/4 ,a process ( ?is sort1 :]e production equals decay1 is call$ a ,,secul> ,,equilibrium4 ,! newly produc$ ,c soon is ev5ly mix$ ) ! c>bon dioxide 9 ! air1 is tak5 up by all liv+ plants1 & !n f9ds its way into all liv+ animals4 ,9 effect1 all c>bon 9 liv+ organisms conta9s a con/ant proportion ( ,c4 ,if any ( ?is c>bon is tak5 out ( circulation--:5 a tree bran* is brok5 (f1 = in/ance1 or :5 a %ellfi% dies 9 ! ocean--no m new ,c is add$ to t p>ticul> sy/em1 b ! old ,c cont9ues to run out4 ,9 effect x n[ />ts measur+ "t z an h\rglass %\ld4 ,illu/ration3 ,to illu/rate secul> equilibrium1 "o mu/ imag9e an h\rglass 9 :i* ! s& 9 ! top bulb is cont9u\sly repl5i%$--z fa/ z x runs out ?r\gh ! hole 9 ! wai/ & disappe>s4 ,:5 we f9d a piece ( *>coal 9 a cave or a piece ( wood 9 "s anci5t /ructure1 = example1 we c measure ! am\nt ( c>bon 9 x1 det]m9e h[ mu* ( x is ,c1 & !n calculate back to ! "t :5 ! radioactivity f ! ,c 0 ! same z we n[ f9d 9 liv+ wood4 ,9 o!r words1 if we assume t we "k f ! obs]v$ secul> equilibrium h[ mu* ,c orig9ally 0 pres5t 9 liv+ mat]ial1 !n we c calculate ! "t ( dea? ( any simil> b anci5t mat]ial4 ,t is ! basis ( ! ,c me?od ( age det]m9ation4 ,illu/ration3 ,d9osaur tracks impr9t$ 9 rock 9 ,navajo ,canyon1 ,arizona1 ar\se ! pr(essional int]e/ ( ?is sci5ti/4 ,fossil traces ( ext9ct prehi/oric creatures 7 = a long "t ! be/ clues to ! age ( rock =mations4 ,illu/ration3 ,a sci5ti/ us+ liquid nitrog5 to freeze c>bon dioxide gas made f a sample ( anci5t mat]ial t he is prep>+ = age det]m9ation by ! c>bon-#ad te*nique4 ,= example1 a bit ( a raft] f a prehi/oric cliff-dwell+ or a remnant ( *>coal f an anci5t fire may be analyz$ = its rema9+ ,c cont5t1 & its age det]m9$ accurately )9 ! m>g9 ( a few hundr$ ye>s4 ,?is fixes ! "t at :i* ! wood = ! raft] or ! firewood 0 brok5 or cut f ! liv+ tree1 & h5ce ! p]iod 9 :i* ! m5 liv$ :o us$ ! wood4 ,illu/ration3 ,! mo/ useful samples = c>bon-#ad age det]m9ation are *>coal1 wood1 & %ells4 ,c>bon-#ad ,c\nt+ ,c>bon-#ad measurem5ts are made by tak+ a kn[n am\nt ( c>bon1 r$uc+ x to a gas1 & !n c\nt+ ! ,c dis9tegrations 9 ! gas4 ,?is may s\nd simple1 b 9 reality ! measurem5t process is a =midable und]tak+1 because ! am\nt ( ! ,c isotope 9 ! c>bon is s extremely small4 7,! rema9d] ( ! c>bon1 ( c\rse1 consi/s ( o!r isotopes--,c or ,c1 :i* are /able47 ,!re are two basic te*niques4 ,! c>bon c be3 #a4 ,burn$ ) oxyg5 to =m c>bon dioxide1 or #b4 ,r$uc$ *emically to me?ane or e?ane1 or to a c>bide f :i* acetyl5e c be evolv$ by add+ wat]4 7,see booklet cov] & description on page #ei47 ,! fir/ te*nique is ! simpl]1 b c>bon dioxide 7,,co7 conta9s only "o atom ( c>bon p] molecule1 :]eas acetyl5e 7,c,h7 & e?ane 7,c,h7 ea* conta9 two4 ,consequ5tly1 ! ,,specific ,,activity ( acetyl5e or e?ane is twice t ( c>bon dioxide1 o!r ?+s be+ equal4 ,= t reason acetyl5e or e?ane are ! pref]r$ gases 9 "s laboratories4 ,on ! o!r h&1 !y are explosive1 & t cautions o!r sci5ti/s into us+ ! c>bon dioxide me?od4 ,:i*ev] gas is us$1 x is fir/ purifi$ & !n /or$ 9 a bottle = a mon? or s4 ,?is /orage all[s = decay 7disappe>ance7 ( any radon1 ! gase\s radioactive product ( uranium decay4 ,uranium contam9ation is difficult to avoid at ! l[ radioactivity levels ( ,c1 b ! half-life ( radon is only #c4hb days1 s t x w decay to an insignificant level 9 a mon?4 ,aft] ! /orage p]iod1 ! gas is pump$ into an array ( in/rum5ts kn[n z a l[-backgr\nd ,,proportional ,,c\nt]1 & its radioactivity is det]m9$4 ,?is is an involv$ process4 ,fir/ !re is ! matt] ( ! ,,backgr\nd ,,c\nt4 ,! backgr\nd c\nt ( an in/rum5t is ! numb] ( pulses 7c\nts7 x w give p] unit "t :5 !re is no radioactive sample 9 x4 ,^! c\nts are caus$ by cosmic rays1 by radioactive contam9ation always f\nd 9 ! vic9ity ( ! c\nt]1 or by any contam9ation inside ! in/rum5t4 ,9 ,c c\nt+1 all ^! s\rces ( backgr\nd mu/ be r$uc$ to negligible levels4 ,?is is done 9 a numb] ( ways4 ,= "o ?+1 ! :ole assembly is con/ruct$ ) surr\nd+ walls ( lead or iron m ?an a foot ?ick4 ,su* a %ield w /op all ! ,,gamma ,,rays com+ f radioactive contam9ation 9 ! laboratory & mu* ( ! cosmic radiation2 high-en]gy cosmic rays & all neutrons /ill w get ?r\gh4 ,!re=e1 !re is an ,,antico9cid5ce ,,r+ inside ! lead %ield4 ,?is is a cyl9drical space completely surr\nd$ by ,,geig] ,,c\nt]s t are connect$ to ea* o!r & to ! ,,sample ,,c\nt] 9 ! middle4 ,) ?is arrangem5t1 :5 ! sample c\nt] & any r+ c\nt] dis*>ge simultane\sly1 x is a signal t ! pulse trigg]+ ?is response 0 caus$ by "s en]getic p>ticles1 su* z a cosmic ray1 pass+ ?r\gh ! :ole assembly4 ,a pulse record$ simultane\sly on two c\nt]s is automatically reject$ f ! c\nt+ me*anisms4 ,"s in/rum5ts h be5 design$ ) a cyl9d] ( p>aff9 imm$iately inside ! antico9cid5ce r+1 to sl[ d[n neutrons s t !y c be captur$1 & ) a f9al %ield ( highly purifi$ m]cury betwe5 two cyl9d]s ( select$ /eel to hold out ev5 m unwant$ radiation4 ,illu/ration3 ,illu/ration3 ,a c>bon-#ad c\nt]4 ,sket* 7above7 %[s arrangem5t ( compon5ts 9 photo 7left74 ,f9ally1 ! sample c\nt]s are made ( specially select$ metal tub+ t is extremely l[ 9 radioactive cont5t1 ) a f9e wire /ret*$ d[n ! middle4 7,9 "s rec5t designs1 ! antico9cid5ce r+ & sample c\nt] are comb9$ 9 a s+le cyl9drical h\s+ ) a ?9 foil ( metalliz$ pla/ic betwe5 !m47 ,a ?9 glass fill+ tube connects ! sample c\nt] ) ! outside _w4 ,illu/ration3 ,detail ( "o type ( sample-c\nt+ tube = c>bon-#ad "w4 ,c>bon-#ad 9 b5z5e gas molecules is plac$ 9 ! c5tral cell & mix$ ) a fluid t sc9tillates1 or emits light fla%es1 :5 expos$ to radiation4 ,photomultipli] tubes conv]t ! fla%es to electric signals4 ,! radioc>bon-be>+ gas is pump$ into ! sample c\nt] ?r\gh ! fill+ tube1 & all ! c\nts result+ f its dis9tegrations are record$ electronically4 ,! age ( ! sample is calculat$ f ! ,,net ,,c\nt+ ,,rate 7! sample c\nt+ rate m9us ! backgr\nd72 ! l[] ! c\nt+ rate ! high] ! age4 ,! upp] limit ( ! age t c be measur$ is det]m9$ by ! ,,/ati/ical ,,error 7t is1 by ! measure ( ! in/rum5t accuracy7 9 ! net c\nt4 ,9 v old samples ?is error may be great en\gh s t ! calculat$ age ( ! sample may h little or no mean+4 ,c>bon-#ad ,results ,,objects ,,dat$ ,,by ,,radioc>bon ,illu/ration3 ,hair ( an ,egyptian woman4 #ejbj #bij ye>s old4 ,illu/ration3 ,l95 wrapp+ f ! ,dead ,sea ,scroll conta9+ ! ,book ( ,isaiah4 #aiag #bjj ye>s old4 ,illu/ration3 ,p]uvian rope4 #bfcb #bjj ye>s old4 ,illu/ration3 ,preglacial wood f\nd 9 ,ohio4 ,m ?an #bj1jjj ye>s old4 ,illu/ration3 ,rope s&al f\nd 9 an ea/]n ,oregon cave4 ,"o ( a pair ( #cjj pairs f\nd 9 ?is cave4 #ijce #cbe ye>s old4 ,c>bon-#ad is by f> ! mo/ widely us$ me?od ( measur+ geologic "t4 ,x has become ! ma9/ay ( ar*eology & geology = /udies ( ev5ts ( ! pa/ #ej1jjj ye>s or s1 & also has wide applications 9 climatology1 ecology1 & geography4 ,x w\ld be difficult to pick out ! mo/ significant example ( ! use ( ?is me?od1 b "o important contribution has be5 9 /udy ( ! e>ly inhabitants ( ,nor? ,am]ica4 ,) ! aid ( ,c x has be5 possible to date human liv+ sites f _m po9ts 9 ! we/]n ,unit$ ,/ates4 ,! fir/ appe>ance ( ^! sites1 ab\t #aa1ejj ye>s ago1 app>5tly co9cid$ ) ! "t :5 a l& bridge 0 op5 f ,asia to ,am]ica ov] :at is n[ ! ,b]+ ,/rait4 ,an ice-free passage ext5d$ f ?is bridge ?r\gh pres5t-day ,alaska & we/]n ,canada to ! ,unit$ ,/ates4 ,?is may h be5 ! r\te tak5 by ! fir/ immigrants to ,am]ica--a population ( mammo?-hunt]s1 :o made ! *>act]i/ic fl9t ,clovis arr[ & spe> po9ts4 ,illu/ration3 ,a ,clovis arr[ po9t *ipp$ f fl9t by ! e>lie/ m5 on ! ,am]ican cont95t4 ,! photograph is actual size4 ,by ab\t #aa1jjj ye>s ago1 ^! ,clovis p _h spread across ! area ( ! ,unit$ ,/ates & into ,mexico4 ,x may h be5 !y :o kill$ (f ! mammo?s & !n gradually assum$ ! *>act]i/ics ( ! ,folsom culture4 ,! ,folsom p 7 bison-hunt]s1 & long 7 ?\ght to h be5 ! fir/ population 9 ,am]ica4 ,x 0 ) ! use ( ,c t x f9ally 0 possible to place ^! two cultures 9 prop] sequ5ce--! ,clovis fir/--& to correlate !m ) major natural *anges1 especially ! advance & retreat ( glaci]s across ! cont95t4 ,,! ,,long-,,liv$ ,,clocks ,all o!r practical age-det]m9ation s*emes are bas$ on a few long-liv$ isotopes1 ) half-lives relatively ne> ! age ( ! e>? 7#d4e ,,aeons74 ,!y are3 ,table ,,iii ,isotope ,emits ,decays to ,half-life ,uranium-#bch #h ,,alpha ,,p>ticles#aj ,lead-#bjf #d4ea aeons ,uranium-#bch ,spontane\s fission #b ,fragm5ts #aj million aeons#aa ,uranium-#bce #g ,alpha p>ticles ,lead-#bjg #j4gac aeons ,?orium-#bcb #f ,alpha p>ticles ,lead-#bjh #ad4a aeons ,rubidium-#hg ,beta p>ticle ,/rontium-#hg #d4g aeons ,potassium-#dj ,electron capture ,argon-#dj #a4c aeons 444444 444444 444444 444444 ,rh5ium-#ahgab ,beta p>ticle ,osmium-#ahg #dj aeons ,x is app>5t t ,table ,,ii on page #f1 %[+ ! long-liv$ radioactive nuclides1 is mu* long] ?an ! li/ ( ! sev5 %[n "h t are actually useful 9 practice4 ,"s ( ! nuclides t are !oretically available are useless on a practical basis1 because !y are s r>e 9 nature4 ,_m o!rs _c be us$ = reasons t are fundam5tal to ! :ole process ( nucle> age det]m9ation by 8:ole h\rglass0 7t is1 p>5t-daught]7 me?ods4 ,let's look at ^! reasons4 ,^! me?ods are bas$ on clos$ sy/ems 9 :i* ! daught] products ( ! radioactive decay are lock$ ) ! p>5t mat]ial f ! beg9n+ ( ! sy/em1 & no?+ is add$ or remov$ !reaft]4 ,to /ate x 9 t]ms ( our analogy1 ! h\rglass mu/ be 9 p]fect work+ ord]--no leaks or cracks p]mitt$4 ,!re is ano!r fundam5tal requirem5t3 ,at ! beg9n+1 ! bottom "p ( ! h\rglass mu/ be empty4 ,if "s s& 7 already 9 ! bottom at ! />t1 we w\ld mi/ak5ly be l$ to conclude t ! "t elaps$ 0 long] ?an x actually 04 ,t necessity places a sev]e limitation on ! type ( sy/em we c use4 ,consid]1 = example1 ! decay ( potassium-#dj into calcium-#dj4 ,measur+ ?is process is p]fectly suitable f ! po9t ( view ( half-life1 b ! daught] product is id5tical ) ! mo/ common isotope ( ord9>y calcium4 ,& calcium is pres5t ev]y:]e 9 nature6 ,ev5 ! pure/ m9]al ( potassium1 sylvite 7! salt1 potassium *loride71 conta9s s mu* calcium impurity t ! ,,radiog5ic daught] calcium1 produc$ by ! decay ( potassium 9 geologic "t1 is negligible 9 comp>ison4 ,we c say t ! bottom ( ?is potassium-#dj h\rglass has be5 /uff$ ) s mu* s& f ! v beg9n+ t ! few gra9s t fall ?r\gh ! wai/ are lo/ 9 ! ov]all mass4 ,?is demon/rates t s*emes involv+ ! decay ( a relatively r>e nuclide into a relatively common "o are n usable4 ,natural geo*emical sep>ations ( elem5ts are nev] p]fect1 anyway4 ,simil>ly1 ! decay ( any ( ! ,,r>e ,,e>? elem5ts into o!r r>e e>? elem5ts is n p>ticul>ly helpful1 because ! r>e e>?s are s simil> *emically !y t5d to travel toge!r :5 !y move 9 nature4#ac ,:]ev] ! p>5t isotope goes1 ! daught] tags along4 ,! ,rubidium-,/rontium ,clock ,! decay ( rubidium-#hg 7,rb7 into /rontium-#hg 7,sr7 is p]haps ! mo/ useful s*eme = geologic age det]m9ation4 ,! same problem %[s up "h1 b at lea/ !re is a way out ( ! wild]ness4 ,x is n exactly simple1 b a consid]ation ( x is fundam5tal to und]/&+ ! process ( nucle> dat+4 ,! figure %[s patt]ns f mass spectromet] *>ts2 ea* peak repres5ts an isotope ( /rontium1 & ! height ( e peak is proportional to ! relative abundance ( t isotope4 ,9 ! figure1 ,a %[s ! mass-spectrum ( a rock or m9]al conta9+ ,,common /rontium 7:i* is a mixture ( sev]al isotopes74 ,! peak ( ,sr is small comp>$ to ! o!rs4 ,b %[s ! mass-spectrum ( /rontium f an old rubidium-ri* m9]al ,,cry/al1 drawn to ! same scale1 z f> z ! nonradiog5ic isotopes1 ,sr1 ,sr1 & ,sr1 are conc]n$4 ,! ,sr peak 9 ?is spectrum is obvi\sly l>g] ?an 9 ! common /rontium 9 ,a4 ,?is is because ?is isotope is radiog5ic & has be5 accumulat+ f ! decay ( rubidium s9ce ?is cry/al 0 =m$4 ,! "q we mu/ answ] is3 ,h[ mu* ( ?is ,sr 0 =m$ f ,rb decay & h[ mu* orig9ally 0 pres5t 9 ! cry/al z an impurity8 ,if ! am\nt ( ?is ,,orig9al /rontium is n too l>ge1 ! problem c be solv$ by simple ari?metic4 ,fir/1 we mu/ f9d a good sample ( common /rontium--t is1 ord9>y /rontium1 ! k9d %[n at left 9 ! figure4 ,we _c require t ?is /rontium be entirely uncontam9at$ by radiog5ic /rontium1 because all /rontium is m or less contam9at$4 ,:at we ne$ is /rontium contam9at$ to j ! same ext5t z ! /rontium t 0 tak5 z an impurity into ! clos$ sy/em :5 x fir/ =m$4 ,9 geological specim5s su* a mat]ial is usually available4 ,illu/ration3 ,draw+s ( mass-spectromet] *>ts %[+ ! isotopic spectra ( two k9ds ( /rontium3 7,a7 common /rontium & 7,b7 /rontium f an old m9]al ri* 9 rubidium4 7,see page #cb = photo ( a mass spectromet]47 ,illu/ration3 ,rubidium-#hg & /rontium-#hg fall on ! same spot 9 ! mass spectrum4 ,!re=e1 rubidium mu/ be sep>at$ *emically f /rontium be=e ! /rontium c be analyz$ 9 a mass spectromet]4 ,x is done ) ion-ex*ange columns4 ,f\r ( !m are %[n 9 ?is photograph4 ,! au?or ( ?is booklet is add+ a sample1 dissolv$ 9 a few drops ( hydro*loric acid1 to ! second column4 ,let u take z our clos$ sy/em a mica cry/al 9 a mass ( granite4 ,mica conta9s a fair am\nt ( rubidium1 & x reta9s its radiog5ic /rontium v well4 ,fur!rmore1 mica cry/als are (t5 associat$ or ev5 int]gr[n ) ! sl5d]1 rod-%ap$ cry/als ( a m9]al call$ apatite--a phosphate ( calcium4 ,x is ju/ifiable1 on ! basis ( geological k1 to say t ! mica & ! apatite grew at r\ghly ! same "t & ?us presumably f ! same liquid m$ium t became granite :5 x lat] solidifi$4 ,n[ /rontium is geo*emically simil> to calcium1 & "s /rontium w h gone into ! apatite cry/al 9 place ( calcium4 ,apatite conta9s no alkalis--h5ce apatite w h virtually no rubidium 7:i* is an alkali7 9 x to contam9ate ! ,sr4 ,consequ5tly1 :5 we f9d apatite 9 an old granite1 we "k ! apatite w /ill conta9 ! k9d ( common /rontium t 0 tak5 into ! mica cry/al :5 x grew orig9ally4 ,we c sep>ate ! apatite f ! granite by /&>d m9]alogical te*niques1 extract ! /rontium f ! apatite *emically1 & analyze x on a mass spectromet] to obta9 ! isotopic spectrum--! relative am\nt ( ea* isotope t is pres5t4 ,we c !n p]=m ! same isotopic analysis on ! /rontium extract$ f ! mica1 & subtract ! orig9al 7apatite7 /rontium f ! total 7mica7 /rontium1 to obta9 ! radiog5ic compon5t or daught] product4 7,see page #cb = details ( ?is me?od47 ,obvi\sly1 !re is a c]ta9 error associat$ ) e isotopic analysis1 s su* a calculation is mean+ful only :5 ! radiog5ic compon5t is l>ge comp>$ ) ! error 9 ! measurem5t ( isotopic abundance4 ,:5 "o l>ge quantity mu/ be subtract$ f ano!r l>ge quantity to obta9 a small diff]5ce1 !re is an obvi\s limit to h[ mu* "o c tru/ ! result4 ,! absolute accuracy 9 measur+ /rontium isotope abundance is a few t5?s ( #a1 us+ ! be/ mass spectromet]s n[ available4 ,9 practice1 "o c tru/ a calculat$ age = a specim5 only :5 ! ,sr is z little z ab\t #e radiog5ic4 ,! results d n mean mu* :5 only #a or #b is radiog5ic4 ,illu/ration3 ,a sample ( granite be+ made ready = cru%+ & m9]al sep>ation4 ,! ,uranium ,fission ,clock ,:5 a neutron /rikes ! nucleus ( uranium-#bce 7,u7 or plutonium-#bci 7,pu71 x may cause ! nucleus to split into two r\ghly equal fragm5ts1 releas+ neutrons & en]gy4 ,?is is ! well-kn[n process ( neutron-induc$ fission1 ! me?od 9 :i* nucle> en]gy is produc$ 9 bo? reactors & bombs4#ad ,! mo/ common uranium isotope1 ,u1 also breaks up by fission1 b does s all by itself1 )\t ! ne$ = any ext]nal neutrons4 ,t process is spontane\s fission & x goes on at r&om1 v mu* l radioactive decay4 ,x is a relatively r>e process & ! fission half-life is long--ab\t #aj million aeons 7#aj ye>s74 ,t means t only ab\t "o spontane\s fission occurs 9 uranium-#bch = e #b million alpha decays4 ,t is en\gh to make a useful clock1 h[ev]1 because ,u is pres5t almo/ ev]y:]e4 7,see ,table ,,iii on page #ai47 ,imag9e an atom ( ,u 9 "s m9]al4 ,:5 ! atom sudd5ly fissions1 x breaks 9 two ) consid]able en]gy1 & ! two fission fragm5ts rip l cannon balls ?r\gh ! surr\nd+ cry/all9e /ructure 9 opposite directions1 creat+ havoc along ! way4 ,!y travel a di/ance some?+ l #aj microns 7#d million?s ( an in*7 be=e !y are f9ally sl[$ d[n & /opp$ by all _! collisions ) o!r atoms4 ,ea* fragm5t's pa? rema9s beh9d z an int5sely damag$ tube ?r\gh ! cry/al4 ,! process 0 kn[n = a long "t be=e anyone 0 able to f9d ^! fission tracks 7! damag$ tubes7 9 ! cry/als4 ,f9ally1 ab\t #aifj1 ?ree "y physici/s1 ,r4 ,l4 ,fleis*]1 ,p4 ,b4 ,price1 & ,r4 ,m4 ,walk]1 work+ at ! ,g5]al ,electric ,rese>* ,laboratory1 fell ^u ! idea ( et*+ fre%ly brok5 surfaces ( cry/als ) acid4 ,!y reason$ t a region s int5sely di/urb$ by ! passage ( a fission fragm5t %\ld be et*$ m easily & deeply ?an ! undi/urb$ surr\nd+ cry/al4 ,t idea turn$ out to be correct1 & fission tracks h n[ be5 f\nd 9 almo/ e common m9]al 7s9ce almo/ all m9]als conta9 small am\nts ( uranium74 ,illu/ration3 ,tracks ( uranium fission f a fossil antelope bone fragm5t f ,hopefield1 ,cape ,prov9ce1 ,s\? ,africa4 ,! fission clock me?od works ?is way3 ,a cleavage face or a poli%$ surface ( a cry/al or glass fragm5t is et*$ ) a suitable solv5t4 ,diff]5t acids "w be/ = diff]5t mat]ials1 & a suitable proc$ure mu/ be develop$ especially = ea* sub/ance4 ,! et*+ br+s out ! fission tracks s !y c be se5 7usually z little conical pits7 & c\nt$ "u a microscope4 ,aft] ?is1 ! sample is expos$ to a kn[n am\nt ( sl[ neutrons#ae 9 a nucle> reactor4 ,new fissions are produc$1 b ?is "t only 9 ,u 7:i* is pres5t 9 all natural uranium 9 ! proportion ( #a atom ( ,u to #acg4g atoms ( ,u71 because sl[ neutrons d n produce fissions 9 ,u4 ,aft] ! neutron irradiation1 ! same surface is et*$ aga91 & ! new tracks c\nt$4 ,! old tracks1 hav+ be5 et*$ twice1 n[ appe> l>g] & ?us c be di/+ui%$ f ! new ones t 7 caus$ by ,u fission4 ,! rate at :i* ,u decays by fission1 f1 is kn[n1 z are ! rate x decays by alpha decay1 1 & ! total numb] ( sl[ neutrons1 n1 to :i* ! sample 0 expos$ 9 ! reactor4 ,! age ( ! cry/al or glass c !n be calculat$3 t 7#a7_/77 ln 7#a 7n,ns7_/7,ni7 con/ant7 :]e ln ! natural log>i?m 7log to ! base e71 ,ns ! numb] ( atoms 9 ! sample4 ,ni ! numb] ( atoms ( ,u 9 ! irradiat$ sample1 & ! con/ant has ! value3 7 #ehb #aj7_/7;f #acg4g7 #d4be #aj ,fission-track dat+ is a br& new te*nique1 /ill only p>tly develop$4 ,x has enorm\s range & is applicable to num]\s m9]als2 ^! advantages imply t x is likely to become v useful4 ,illu/ration3 ,an atomic absorption spectrophotomet] is us$ to measure ! am\nt ( potassium 9 samples ( mica dissolv$ 9 acid4 ,plumbology ,! mo/ complicat$ & !re=e probably ! mo/ int]e/+ decay s*eme ( all is ! decay ( uranium to lead1 discov]$ well ov] half a c5tury ago & /ill int5sively /udi$4 ,!re are sev]al reasons = ! int]e/4 ,fir/1 uranium & lead are geo*emically sep>at$ to a high degree1 n only on ! small scale ( an ore deposit b also on ! scale ( ! e>? z a :ole4 ,second1 natural uranium has two isotopes ) half-lives t are nei!r too long nor too %ort to be useful 7! great] half-life almo/ exactly equal+ ! age ( ! e>?71 & ^! half-lives diff] f ea* o!r by a factor ( ab\t #f4c4 ,t leads to v important consequ5ces1 z we %all see4 ,?ird1 uranium & lead are bo? common1 & te*niques are available = extract+ !m 9 measurable quantities f almo/ any natural mat]ial4 ,z a consequ5ce ( ^! happy circum/ances1 ! /udy ( uranium & lead has contribut$ a great deal to und]/&+ ! e>?'s hi/ory & ! processes t g on inside x4 ,f4 ,g4 ,h\t]mans1 "o ( ! great pione]s 9 ?is /udy1 jok+ly call$ ! me?od ,,plumbology1 & x seems a useful "n4 ,,! ,,age ,,( ,,! ,,e>? ,! greate/ a*ievem5t ( ! 8plumbologi/s0 has be5 ! calculation ( ! age ( ! e>?1 fir/ propos$ by ,h\t]mans1 a ,g]man physici/1 & indep5d5tly by ,ar?ur ,holmes1 a ,briti% geologi/1 9 #aidf & f9ally p]fect$ by ,c4 ,c4 ,patt]son 9 #aiec4 ,x is actually a r simple calculation1 al?\gh ! way to discov]+ x 0 f> f easy4 ,be=e we look at x 9 detail1 h[ev]1 let's consid] "s basic assumptions & expla9 :at is meant by 8! age ( ! e>?04 ,f /udy+ ! me*anics ( ! sol> sy/em1 sci5ti/s h become reasonably c]ta9 t ! e>? & ! o!r planets & _! satellites all 7 =m$ 9 a common process 9 a relatively %ort p]iod ( "t1 geologically speak+4 ,p]haps x took a doz5 million ye>s or s1 b comp>$ to ! "t t has elaps$ s9ce1 t is a tw9kl+4 ,at "s "t soon aft]w>ds1 ! e>? became molt51 or at any rate fluid en\gh to all[ mu* ( its iron to settle t[>d ! c5t] to =m ! e>?'s core4 ,simil> cores presumably =m$ 9 o!r planets4 ,z ! iron w5t d[n1 x took "s lead ) x1 & z ! silica w5t up1 uranium foll[$ x t[>d ! surface1 because ( ! *emical aff9ity betwe5 ^! k9ds ( elem5ts4 ,9 ! pres5t e>?1 we h f\nd1 almo/ all ! uranium is conc5trat$ 9 ! top lay]1 or cru/1 :i* is only ab\t #be miles ?ick "u ! cont95ts & ev5 ?9n] "u ! oceans4 ,illu/ration3 ,int]nal /ructure ( ! e>?4 ,! c5tral core is probably an alloy ( iron & nickel1 surr\nd$ by a mantle ( less d5se silicate mat]ial1 ) a ?9 cru/ ( /ill light] silicates4 ,! "t ( ?is e>ly & relatively rapid sep>ation ( uranium & lead on a worldwide scale is ! ev5t t plumbologi/s c det]m9e1 & ! p]iod s9ce !n is :at !y mean by 8! age ( ! e>?04 ,:5 ,h\t]mans fir/ wrote ab\t x1 he call$ x 8! age ( uranium04 ,h[ is ?is done8 ,we h said t "o ( ! isotopes ( uranium1 ,u1 decays fa/]--ab\t #f4c times fa/]--?an ! o!r1 ,u4 ,!y decay into two diff]5t isotopes ( lead4 ,!re=e1 if we c det]m9e ! isotopic composition ( av]age ord9>y lead 9 ! e>?'s cru/ today1 & if we c someh[ obta9 a sample ( ! k9d ( lead t is lock$ 9 ! e>?'s core1 we c calculate h[ long x took to *ange ! ,,primordial lead 7l t 9 ! core7 into pres5t-day lead 9 ! cru/ by ! gradual addition ( radiog5ic lead--lead t has result$ f ! decay ( uranium4 ,n[1 someone might logically ask1 8,isn't x necess>y to "k also ! actual am\nt ( uranium involv$ 9 ! process1 & isn't ?is difficult to det]m9e80 ,x turns out to be a rem>kable aspect ( ! ,holmes-,h\t]mans calculation t ! uranium-conc5tration t]ms cancel out 9 ! equations & only ! ratio ( ! isotopes & _! decay con/ants ne$ be consid]$4 ,^! are all kn[n accurately4 ,next1 we mu/ decide j :at is av]age pres5t-day lead8 ,x isn't en\gh to g to a lead m9e & get a sample1 because1 un=tunately1 leads f diff]5t m9es h widely v>i$ isotopic composition--t is1 a diff]5t mixture ( f\r natural isotopes1 ,pb1 ,pb1 ,pb1 & ,pb--z a result ( _! geologic hi/ories4 ,no1 lead samples f a m9e won't d4 ,h[ev]1 geologi/s h be5 able to sep>ate lead f rec5t m>9e s$im5ts1 obta9$ f ! ocean bottom1 f> f l&4 ,^! are ( uni=m composition1 & are good samples ( :at ! _w's riv]s br+ into ! ocean4 ,o!r useful samples c be f\nd 9 plateau basalts1 :i* are enorm\s bodies ( d>k volcanic rock t make up ! b$rock 9 _m p>ts ( ! _w4 ,! lead f ^! basalts is isotopically v mu* l ! lead 9 ! oceans4 ,v well1 b h[ ab\t ! lead f ! core8 ,:]e c we hope to f9d a sample ( x8 ,x turns out to be easi] ?an y might ?9k4 ,a/ronom]s believe x highly probable t mo/ meteorites are fragm5ts ( a =m] planet t broke up = reasons t are n entirely cle>4 ,x is pretty def9ite1 h[ev]1 t ?is protoplanet 7or ^! protoplanets1 = !re may h be5 m ?an "o7 _h an iron core1 & ?is core 7or ^! cores7 is ! s\rce ( ! iron meteorites sail+ ar\nd 9 space4 ,a l>ge meteorite hit ! e>? n too long ago 7geologically speak+7 & caus$ ! ,meteor ,crat] ne> ,canyon ,diablo 9 ,arizona4 ,illu/ration3 ,exam9+ ocean-bottom s$im5ts obta9$ by l[]+ a tube-l in/rum5t t br+s up a long rod-%ap$ 8core01 prior to nucle> age det]m9ation ( ! sample4 ,_m fragm5ts ( ! meteorite iron h be5 f\nd ar\nd ! crat]1 & x is reasonable to assume t ?is is ! k9d ( iron we w\ld expect to f9d 9 ! core ( ! e>?4 ,l ! core iron1 x is mix$ ) a little lead1 :i* c be isolat$ & analyz$ 9 a mass spectromet] = its isotopic composition4 ,?is lead is f\nd to be mu* less contam9at$ ) radiog5ic lead1 & h5ce is mu* m primitive ?an ! olde/ leads f\nd on e>?4 ,?us1 meteorites presumably are z close z we c get to true primordial lead--! lead ( ! "t :5 ! e>? 7& ! protoplanet7 fir/ =m$4 ,once ^! measurem5ts 7 available1 x 0 easy to write ! ,h\t]mans equation = pres5t-day & primordial leads 9 ?is way3 77,pb7_/7,pb77 pres5t - 77,pb7_/7,pb77 primordial ------------------------ -------------------------- 77,pb7_/7,pb77 pres5t - 77,pb7_/7,pb77 primordial #acg4g 77e#bcht - #a77_/77;e#bcet - #a77 ,! pres5t ratio ( ,u to ,u is #acg4g4 e ! base ( natural log>i?ms ! ,,decay ,,con/ant ( ea* isotope ( uranium t ! age ( ! e>?4 ,sub/itut+ ! be/ exp]im5tal lead isotope ratios into ! equation & solv+ = t1 ,patt]son 0 able to calculate t ! e>? is #deej million ye>s 7#d4ee aeons7 old4 ,subsequ5t calculations bas$ on o!r proc$ures g5]ally h confirm$ t result4 ,analytical ,te*niques ,ea* me?od ( nucle> age det]m9ation involves a diff]5t sequ5ce ( sample prep>ation4 ,wood1 peat1 *>coal1 bones1 or %ells are clean$ = c>bon-#ad dat+ 9 ord] to remove e trace ( possible contam9ation by mod]n c>bon z well z extrane\s old c>bon4 ,rocks are cru%$ & gr\nd1 m9]als are sep>at$ accord+ to :at is ne$$ 9 any p>ticul> /udy1 & ! desir$ elem5ts are extract$ & sep>at$ by *emical proc$ures4 ,(t5 !re may be sev]al diff]5t ways ( do+ ! same ?+2 diff]5t laboratories use diff]5t proc$ures4 ,9 e case1 h[ev]1 long & complicat$ proc$ures mu/ be foll[$ be=e results are obta9$ f :i* an age c be calculat$4 ,!re is no su* ?+ z a black box into :i* y c ?r[ a rock & read its age on a dial6 ,( all ! elem5ts t are "p ( ! useful p>5t-daught] sy/ems1 only potassium is common en\gh to be analyz$ by conv5tional *emical te*niques4 ,all ! o!r elem5ts1 especially ! radiog5ic ones1 are pres5t 9 su* small quantities t special processes _h to be develop$ to measure !m4 ,! mo/ valuable & g5]ally us$ process is call$ ,,isotope ,,dilution4 ,isotope ,dilution ,?is is a process = analyz+ an unkn[n mat]ial by incorporat+ uni=mly into x a small am\nt ( a radioactive te/ sub/ance & det]m9+ h[ mu* ! trac] radioactivity is alt]$ by dilution 9 ! orig9al mat]ial4 ,x works l ?is3 ,let's say t we h an unkn[n numb] ( atoms1 x1 ( a giv5 elem5t4 ,! normal isotopic composition ( ?is elem5t is accurately kn[n1 z x is = mo/ elem5ts1 & ! ratio ( two ( its isotopes c be express$ z ,a_/,b4 ,we n[ add to x a kn[n 7b usually small]7 am\nt1 c1 ( ! same elem5t4 ,?is quantity has a dra/ically diff]5t isotopic ratio1 ,a_/,b4 ,we mix x & c ?or\ghly toge!r4 ,! ratio ,a_/,b c h almo/ any value1 b mu/ be diff]5t f ,a_/,b & we mu/ "k exactly :at x is4 7,!re are _m ways ( det]m9+ ?is *emically1 or we c use a sample isotope ( kn[n composition obta9$ f ! ,u4 ,s4 ,atomic ,en]gy ,commission's ,oak ,ridge ,national ,laboratory at ,oak ,ridge1 ,t5nessee47 ,! sub/ance add$ is kn[n colloquially z ! ,,spike4 ,aft] ! orig9al mat]ial & ! spike are ?or\ghly mix$ we h3 x7,a_/,b7 c7,a_/,b7 7x c7 7,a,b7 9 :i* ,a_/,b w be ! ratio ( ! two isotopes 9 ! mixture4 ,) ?is in=mation 9 h&1 we c p]=m any *emical purification or transf] process ) ! mat]ial 7see photo on page #bb71 )\t hav+ to worry ab\t loss4 7,ev5 if #ij ( ! mat]ial %\ld be lo/ 9 "s op]ation1 ! isotopic composition w\ld n be *ang$1 & t is all we are int]e/$ 947 ,n[ we c place ! mat]ial conta9+ ! isotopic mixture 9 a ,,mass ,,spectromet]1 :i* w det]m9e ! ratio ,a_/,b4 ,:5 we h t1 we may sub/itute ! value ( ,a_/,b 9 ! equation & quickly calculate x1 ! unkn[n conc5tration ( atoms 9 ! orig9al sample4 ,illu/ration3 ,a l>ge 7#ab-;in*7 mass spectromet] 7at left7 9 use4 ,electronic equipm5t 7"r7 *>ts results 7see page #ba74 ,illu/ration3 ,ess5tial p>ts ( a mass spectromet]4 ,atoms to be analyz$ are *ang$ to ions 9 ! s\rce4 ,!n ! ions are accel]at$ by high voltage1 deflect$ 9 a magnetic field accord+ to _! mass1 & ! int5sity ( ! sep>at$ beams is measur$ 9 ! collector4 ,mass ,spectrometry ,! mass spectromet] measures isotopic abundances us+ a magnetic field to sort electrically *>g$ p>ticles into gr\ps accord+ to _! masses4 ,x works ?is way3 ,a small drop ( mat]ial to be analyz$ is plac$ on a metal filam5t & dri$4 ,! filam5t1 9 its hold]1 is plac$ inside ! mass spectromet]1 & heat$ electrically 9 a vacuum1 l ! filam5t 9 a light bulb4 ,z ! wire beg9s to gl[1 "s ( ! sample beg9s to radiate1 or 8boil (f01 los+ an electron or two 9 ! process4 ,9 o!r words1 "s ( ! atoms w be *ang$ into positive ,,ions4 ,an alt]native me?od is to introduce ! sample mat]ial into ! vacuum *amb] 9 ! =m ( a gas 7l argon1 = example71 & !n bomb>d ! gas ) electrons /ream+ f a hot filam5t4 ,! electron /ream w knock "s electrons (f ! gas molecules & ?is also w produce positive ions4 ,ei!r process ( ion production is satisfactory1 dep5d+ on ! problem to be tackl$1 b ! mass spectromet]s = ! two me?ods are naturally q diff]5t4 ,:i*ev] way ! ions 7 produc$1 !y are next expos$ to a /rong electric field1 accel]at$1 & electro/atically focus$ into a beam4 ,^! *>g$ p>ticles are direct$ into a magnetic field betwe5 ! pole faces ( an electromagnet4 ,! magnet does ! analyz+ by ! pr9ciple ( magnetic deflection t 0 kn[n to ,&r ,amp]e & ,mi*ael ,f>aday m ?an a c5tury ago4 ,any mov+ electric *>ge has a magnetic field associat$ ) x4 ,?is field int]acts ) ! field ( ! analyz+ magnet to impress a deflect+ =ce on ! *>ge4 ,! =ce acts at "r angles to ! direction ! *>ge travels & also at "r angles to ! direction ( ! impress$ magnetic field4 ,! pull ( ?is =ce dep5ds only on ! electric *>ge & ! spe$ ( ea* p>ticle3 ,a light s+le-*>g$ p>ticle w be deflect$ m ?an a heavi] p>ticle ) ! same *>ge4 ,9 ?is way1 ! ions 9 ! beam are sort$ out into a numb] ( sep>ate beams1 ea* made up ( p>ticles ( ! same *>ge_/mass ratio4 ,ea* beam conta9s "o isotope ( ! orig9al mat]ial1 because isotopes diff] on ! basis ( _! mass4 ,by adju/+ ! curr5t 9 ! electromagnet we c direct ^! sep>ate beams into a 8collector0 & electrically measure _! int5sity "o by "o4 ,?is gives ! relative abundance ( ! sep>ate isotopes 9 ! sample4 ,m9]als ,t ,c ,be ,dat$ ,measur+ age by "o ( ! long-liv$ radioisotopes requires a clos$ sy/em4 ,usually ?is is "s k9d ( cry/al =m$ 9 a p]iod ( "t t is %ort1 comp>$ to ! "t t has elaps$ s9ce1 & t has rema9$ un*ang$ s9ce x =m$4 ,specifically1 nei!r ! p>5t isotopes c h be5 add$ nor ! daught] isotopes remov$ by any process o!r ?an radioactive decay4 ,! e>? is a dynamic sy/em1 h[ev]4 ,?+s are always *ang+ & mov+--n v rapidly1 p]haps1 b fa/ en\gh1 9 geologic "t1 to raise m\nta9s & %ift oceans4 ,solutions are mov+ ar\nd1 dissolv+ some?+ "h & deposit+ x aga9 some:]e else4 ,temp]atures are *ang+ z "o place is d5ud$ by erosion & ano!r area buri$ "u lay]s ( s$im5t4 ,"u su* conditions1 few sy/ems rema9 clos$4 ,x is p]haps surpris+ t we f9d any clos$ sy/ems at all4 ,let u look at a few t are kn[n to be reliable4 7,!y are li/$ 9 ,table ,i on page #d47 ,pota% ,feldsp> ,9 ! e>ly #aiejs1 :5 ! potassium-argon 7p>5t-daught]7 me?od 0 be+ develop$ by sci5ti/s at ! ,univ]sity ( ,*icago1 x 0 ?\ght t ! pota%-be>+ v>iety ( ! m9]al feldsp> w\ld be an ideal clos$ sy/em1 because x 0 usually optically cle> & free ( flaws4 ,?is widely %>$1 logical1 & p]fectly sci5tific d$uction soon turn$ out to be q wrong4 ,! sci5tific work]s discov]$ t :5 feldsp> & mica f ! same rock 7& ?us ( ! same age7 7 analyz$ side by side1 ! mica always came out old]6 ,inve/igation %[$ t feldsp> 8leak$0 argon 7lo/ "s ( its radiog5ic argon7 ev5 at room temp]ature1 b ! mica reta9$ all or ne>ly all ( ! argon t _h be5 g5]at$ 9 x4 ,mica ,) ! developm5t ( ! rubidium-/rontium 7p>5t-daught]7 me?od by ,l4 ,t4 ,aldri* & 8 co-work]s at ! ,c>negie ,in/itution ( ,wa%+ton1 came ! realization t mica 0 also v useful = ?is analysis1 = x usually conta9s ample rubidium & n mu* orig9al /rontium t w\ld mask ! pres5ce ( ! radiog5ic /rontium4 ,z a result1 mica1 especially black mica 7! m9]al biotite71 has enjoy$ great popul>ity z a good & easy-to-f9d clos$ sy/em4 ,illu/ration3 ,a sci5ti/ mak+ adju/m5ts on an 8argon tra901 a maze ( glass tub+ 9 :i* argon is releas$ f m9]als & purifi$ = analysis4 ,ev]y?+ has its limits1 & mica is no exception3 ,ev5 mica t5ds to leak argon at elevat$1 b /ill relatively l[ 7geologically speak+71 temp]atures4 ,^! effects also dep5d on pressure & o!r factors1 n all ( :i* are well kn[n2 ^! elevat$ temp]atures1 pressures & o!r conditions ( c\rse act to "s ext5t on all rocks buri$ 9 ! e>?'s cru/4 ,x is kn[n t at only ab\t #cjj;,c at mod]ate pressures argon is leak$ f mica fa/] ?an x is be+ g5]at$ 9 x by ! decay ( radioactive potassium4 ,! temp]ature ne$$ to cause ! rapid loss ( /rontium f mica is n mu* high]4 ,mica1 especially biotite1 w recry/allize & lose all its radiog5ic con/itu5ts 7argon & /rontium7 at temp]atures :]e _m o!r m9]als %[ little or no *ange4 ,t means t we _c always rely on mica to give ! date ( ! orig9al cry/allization ( a rock--! "t :5 x cool$ f a molt5 /ate4 ,in/ead1 mica w tell u :5 ! rock la/ cool$ f1 say1 sev]al hundr$ degrees c5tigrade1 reg>dless ( :at may h happ5$ to ! rock be=e t4 ,! mica may h be5 reheat$ z a result ( be+ buri$ "u a few miles ( s$im5t1 = example4 ,! mica w %[ :5 ! rock la/ cool$--9 o!r words1 :5 x came up aga94 ,l[-,/rontium ,feldsp> ,9 spite ( e>ly disappo9tm5ts ) pota% feldsp> = argon dat+1 "s ( x is useful = rubidium-/rontium proc$ures4 ,x all dep5ds on h[ mu* orig9al /rontium ! pota% feldsp> conta9s4 ,mo/ feldsp>s1 un=tunately1 conta9 f> too mu*1 b rapid scre5+ by ,x-ray fluoresc5ce or flame photometry me?ods c we$ ^! out & id5tify specim5s l[ en\gh 9 orig9al /rontium to be useful4 ,o!rwise1 feldsp> is an excell5t clos$ sy/em = rubidium & /rontium2 x rema9s clos$ ev5 at temp]atures high en\gh to melt _m o!r m9]als4 ,x is n affect$ at all by ! same degree ( heat+ t w drive argon out ( biotite4 ,! rubidium-/rontium age ( feldsp> usually comes close to ! "t ( orig9al cry/allization ( ! rock4 ,obvi\sly1 "h is a geologically important tool4 ,if we f9d feldsp> & biotite 9 "o rock1 & if feldsp>1 te/$ by ! rubidium-/rontium me?od gives ! same age z biotite te/$ by potassium-argon decay1 !n we c say ) confid5ce t ! rock has n be5 reheat$ s9ce %ortly aft] x cry/alliz$4 ,conv]sely1 if ! biotite comes out mu* y\ng] ?an ! feldsp>1 we c be sure t some?+ has happ5$ to ?is rock long aft] x fir/ cry/alliz$4 ,su* in=mation is n only valuable to pure sci5ce--x c also be useful 9 locat+ areas favorable = ore prospect+ & 9 o!r practical ways4 ,zircon ,ano!r v int]e/+ m9]al is zircon 7a silicate ( zirconium71 "o ( ! accessory m9]als f\nd 9 small quantities 9 _m cry/all9e rocks4 ,zircon usually occurs 9 v small gra9s & is heavy & h>d1 s t x c be sep>at$ f ! o!r rock )\t mu* difficulty1 ev5 ?\gh x may take #ajj p\nds ( rock to supply a gram ( zircon4 ,zircon usually conta9s a fair am\nt ( uranium & v little lead4 ,x holds radiog5ically produc$ lead well1 ev5 at relatively high temp]atures4 ,b t is n all4 ,ev5 if "s ( ! lead is lo/1 !re is a ma!matical way ( correct+ = x4 ,?is te*nique is call$ ,,concordia ,,analysis & 0 develop$ by ,g4 ,w4 ,we!rill1 a physici/ !n at ! ,c>negie ,in/itution ( ,wa%+ton4 ,x is bas$1 aga91 on ! fact t natural uranium has two long-liv$ isotopes--,u & ,u--& t ! light] "o1 ,u1 decays fa/] ?an ! heavi]4 ,! daught] products ( bo? uranium decay processes are isotopes ( ! same elem5t1 lead--,pb & ,pb1 respectively4 ,heavy isotopes are n sep>at$ to any significant degree by *emical processes1 s t if radiog5ic lead has be5 lo/ f a sy/em = any reason1 ! o!r lead isotopes also w h be5 lo/ 9 :atev] proportion !y 7 pres5t orig9ally4 ,if we plot a graph ( ! radiog5ic ,pb_/,u ratio aga9/ ! radiog5ic ,pb_/,u ratio = concordant 7clos$7 sy/ems ( all ages1 we obta9 ! curv$ l9e %[n 9 ! figure bel[4 ,! curve is ! locus ( all concordant ,u-,pb ages & is call$ ,concordia4 ,!n if we te/ two or m p>ticul> zircons ( ! same age t h lo/ diff]5t am\nts ( lead1 at ab\t ! same "t1 ! plot ( _! ,pb_/,u ratios aga9/ _! ,pb_/,u ratios w fall on a /raight l9e t is a *ord ( ! ,concordia curve4 ,! upp] int]section ( ?is *ord ) ! curve !n w m>k ! true age ( ! zircons4 ,?is is an elaborate te*nique utiliz+ difficult *emical proc$ures1 b x has prov$ invaluable 9 solv+ "s important geologic problems4 ,illu/ration3 ,! ,concordia curve (f]s a useful way ( analyz+ results ( age det]m9ations on ! m9]al zircon4 ,hornbl5de ,! m9]al hornbl5de provides ano!r useful sy/em4 ,hornbl5de is a complex silicate ( sodium1 calcium1 iron1 magnesium1 & alum9um1 & usually conta9s a few t5?s ( #a ( potassium4 ,x is unusual 9 t x t5aci\sly reta9s its radiog5ic argon1 ev5 at relatively high temp]atures4 ,sanid9e ,/ill ano!r good sy/em is ! r>e feldsp>1 sanid9e1 :i* is excell5t = bo? potassium-argon & rubidium-/rontium age det]m9ation4 ,sanid9e usually is f\nd 9 volcanic a% falls & has be5 important 9 ! e/abli%m5t ( ! geologic "t scale1 z we %all see4 ,:ole ,rocks ,f9ally !re is /ill ano!r way ( obta9+ a clos$ sy/em by us+ ! :ole rock1 n j a cry/al ( a s+le m9]al )9 x4 ,a l>ge body ( granite or simil> rock may conta9 a numb] ( m9]als1 "s or none ( :i* may be clos$ sy/ems4 ,yet z long z ?is body ( rock rema9s imp]meable to solutions 7:i* 9 nature means mo/ly to wat]71 no sub/ance w be able to move v f> 9 x because diffusion 9 solids is s sl[4 ,consequ5tly x w rema9 a clos$ sy/em1 z a :ole1 reg>dless ( :at happ5s to ! individual m9]al gra9s4 ,if we take a piece f ne> ! middle ( ?is body ( rock & if ?is piece is mu* l>g] ?an ! l>ge/ con/itu5t gra9 9 x1 !n we h a fair sample ( a clos$ sy/em--! :ole rock4 ,! only difficulty arises f ! fact t few rocks are suffici5tly imp]meable to solutions to reta9 argon1 & _m rocks conta9 s mu* common /rontium t rubidium-/rontium analysis is impractical4 ,/ill1 we c use ! rapid survey me?ods z = feldsp>1 select+ ! few rocks t w\ld be useful4 ,?is "w has be5 done frequ5tly1 & ! results h be5 fruitful = rubidium-/rontium analysis4 ,! :ole-rock rubidium-/rontium age dates ! "t :5 ! rock became imp]meable4 ,,"s ,,int]e/+ ,,results ,! ,old ,man f ,olduvai ,illu/ration3 ,fossil skull ( ,z9jan?ropus1 ne>ly #b1jjj1jjj ye>s old1 discov]$ 9 #aiei by ,dr4 ,l4 ,s4 ,b4 ,leakey 9 ,olduvai ,gorge4 ,accurate dat+ ( ?is e>lie/ human ance/or 0 possible by us+ ! potassium-argon me?od4 ,"o ( ! mo/ talk$-ab\t age measurem5ts 9 rec5t ye>s 0 ! det]m9ation ( ! unexpect$ly great age ( fossil ance/ors ( man1 f\nd by ! ,briti% an?ropologi/1 ,dr4 ,l4 ,s4 ,b4 ,leakey1 9 ,olduvai ,gorge 9 ,tanzania4 ,! measurem5ts 7 made by ,g>niss ,h4 ,curtis & ,jack ,f4 ,ev]nd5 at ! ,univ]sity ( ,cali=nia 9 ,b]keley by ! potassium-argon me?od4 ,! age came out a little less ?an #b million ye>s1 ab\t twice z old z x 8%\ld be0 9 ! view ( _m sci5ti/s4 ,human rema9s ( su* great antiquity _h nev] be5 f\nd be=e1 & mu* d\bt 0 rais$ ab\t ! validity ( ! figures4 ,"t p]iods z %ort z two million ye>s are n easy to measure by potassium-argon4 ,! am\nt ( argon produc$ 9 t "t is extremely small1 & contam9ation by argon f ! air is a s]i\s problem4 ,/ill1 ! measurem5ts 7 repeat$1 ! rocks 7 /udi$ aga91 & ! result did n *ange3 ,! fossils 7 /ill ab\t #b million ye>s old4 ,9 cases l ?is1 "o tries to f9d "s o!r me?od to *eck ! results 9 an indep5d5t way4 ,aft] _m attempts x 0 discov]$ t ! same rock /rata dat$ by potassium-argon also conta9$ "s pumice--a por\s volcanic glass--& t ?is glass 0 suitable = uranium fission-track dat+4 ,! measurem5ts 7 made 9 ! ,g5]al ,electric ,rese>* ,laboratory4 ,:at 0 ! result8 ,j ab\t #b million ye>s6 ,:5 su* altoge!r diff]5t te*niques give ! same numb]1 "o c h "s confid5ce t ! numb] is exact4 ,x w\ld be difficult to imag9e a di/urbance 9 nature t w\ld cause ^! unrelat$ me?ods to give ! same wrong numb]--9 bo? cases by a factor ( two4 ,! d\ble *eck simply means ! ,olduvai man is #b million ye>s old4 ,!re is n mu* d\bt ab\t x4 ,! ,geologic ,"t ,scale ,mu* ( hi/orical geology is bas$ on a relation%ip call$ ! ,,law ,,( ,,sup]position4 ,?is simply means t :5 "s rock =mation 0 plac$ on top ( "s o!r =mation by natural processes 7s$im5tation or volcanic eruption1 = example71 ! lay] on top mu/ be y\ng] ?an ! "o on ! bottom4 ,su* a conclusion may n[ seem obvi\s1 b ! concept 0 n ev5 express$ until ! v end ( ! eighte5? c5tury & 0 /ill a matt] ( sci5tific controv]sy :5 ,abraham ,l9coln 0 a boy4 ,x 0 ! law ( sup]position1 h[ev]1 t l$ ! e>ly geologi/s to e/abli% ! fir/ geologic "t scales & to realize ! enorm\s ext5t ( geologic "t4 ,illu/ration3 ,diagram illu/rat+ ! law ( sup]position4 ,ea* rock b$ is y\ng] ?an ! /rata "u x4 ,9 ess5ce ! sy/em ( e/abli%+ age by ?is concept is ?is3 ,some:]e a l>ge & easily recogniz$ lay] ( s$im5t>y rock 0 kn[n4 ,x _h a *>act]i/ic color1 texture1 gross composition1 & ov]all appe>ance4 ,let u call x b$ ,m4 ,?is b$ c\ld be trac$ across ! c\ntryside until a place 0 rea*$ :]e x c\ld be se5 t b$ ,m re/$ on ano!r1 diff]5t lay] ( rock1 :i* we might call b$ ,l4 ,b$ ,l c\ld also be trac$ "s di/ance & ultimately c\ld be obs]v$ re/+ on a /ill diff]5t /ratum1 :i* we %all call b$ ,k4 ,"s ( ^! b$s _h fossils 9 !m1 & x 0 ev5tually realiz$ t rocks ) ! same k9ds ( fossils are ( ! same age1 ev5 ?\gh !y may diff] 9 o!r respects--9 color or composition1 = in/ance4 ,if b$ ,m 0 foll[$ 9 ano!r direction1 p]haps a po9t 0 rea*$ :]e x dipp$ d[n a little1 & "h1 0 f\nd /ill ano!r lay]--call x b$ ,n--on top ( ,m4 ,obvi\sly1 ! sequ5ce ( b$s f olde/ to y\nge/ 0 ,k-,l-,m-,n4 ,_! relative ages 7 n[ e/abli%$4 ,ov] ! ye>s1 hundr$s ( geologi/s describ$ v>i\s rock lay]s & id5tifi$ ! fossils 9 !m4 ,by ! middle ( ! n9ete5? c5tury1 ?is 8lay]-cake0 /ructure ( s$im5t>y rocks 0 well-kn[n 9 we/]n ,europe4 7,"o may say1 p>5!tically1 t ,am]ica 0 geologically a va/ unkn[n at t "t4 ,today we "k mu* m ab\t ! geology ( ,ant>ctica ?an anyone a hundr$ ye>s ago knew ab\t ! geology ( ! ,unit$ ,/ates47 ,a sy/em ( nom5clature = ! 8lay]-cake0 0 develop$ & ref9$4 ,gradually ?is nom5clature 0 accept$ int]nationally4 ,long-range correlations betwe5 b$s ( ! same age1 di/ant halfway ar\nd ! globe f ea* o!r1 7 made possible z ! sci5ce ( ,,paleontology develop$4 ,! relative age ( almo/ any rock conta9+ ev5 poorly pres]v$ fossils c\ld be det]m9$ any:]e 9 ! _w ) precision4 ,t is1 ! age ( rock lay]s 9 relation to "o ano!r 0 kn[n4 ,b ! real age--! absolute age--rema9$ unkn[n until k ( radioactivity provid$ ! necess>y clocks4 ,illu/ration3 ,a geologi/ c>efully maps ! lay]s ( soil 9 :i* anci5t fl9t tools h be5 f\nd4 ,exact correlation ( ! tool-be>+ /rata ) mat]ial datable by c>bon-#ad analysis mu/ be accompli%$ be=e ! age ( ! tools c be det]m9$4 ,ev5 ?is process wasn't entirely )\t problems4 ,! difficulty lay 9 ! fact t ord9>y s$im5t>y rocks 7%ale1 s&/one1 & lime/one7 _c be dat$ by ! usual nucle> me?ods because !y pres5t no suitable clos$ sy/ems4 ,only "s volcanic s$im5ts c be reliably dat$ by ! mica1 feldsp>1 & zircon !y conta92 b ^! anci5t a%falls are r>e1 usually are only a few in*es ?ick1 & are n easy to id5tify at ! surface because !y wea!r quickly to clay4 ,only ab\t a doz5 volcanic b$s h be5 accurately dat$ 9 ,nor? ,am]ica4 ,! "t po9ts !y e/abli%$ are ma9/ays ( ! pres5t geologic "t scale1 b !y h _h to be supplem5t$ by indirect in=mation4 ,illu/ration3 ,/eeply dipp+ s&/one /rata f ! ,cretace\s ,p]iod ne> ,gallup1 ,new ,mexico4 ,?is photo1 tak5 9 #aija 7note ! horse-drawn wagon71 0 made on an e>ly gov]nm5t survey ( ,we/]n l&s4 ,illu/ration3 ,fossils ( bird tracks 9 s&/one 9 ,dea? ,valley1 ,cali=nia4 ,! mo/ important ( ^! indirect "t po9ts are furni%$ by :at geologi/s call ,,bracket$ ,,intrusives4 ,x (t5 happ5s 9 geologic hi/ory t a mass ( rock becomes molt5 at a great dep? & =ces its way up ?r\gh sev]al lay]s ( s$im5t>y rocks4 ,! s$im5t>y lay]s are usually b5t & twi/$ 7fold$7 by ! up?ru/1 & :]e ! cool] rock comes 9 contact ) ! molt5 mass1 cool] mat]ial is burn$ 7recry/alliz$74 ,geologi/s call t process ,,contact ,,metamorphism because ! s$im5t>y rock =ms are *ang$1 or metamorphos$1 to h ano!r =m or composition4 ,contact-metamorphos$ rocks1 9 spite ( ! damage !y h suff]$1 may conta9 recognizable & accurately datable fossils4 ,!reby ! metamorphic rock e/abli%es a l[] limit = ! age ( ! intrusion3 ,x mu/ be y\ng] ?an ! fossils 9 ! y\nge/ ( ! metamorphic rocks x t\*$4 ,n[ on top ( ! intrusive rock1 we may f9d ano!r s$im5t>y rock1 deposit$ on top ( ! intrusive aft] x cool$ & 0 expos$ by ! erosion ( ov]ly+ mat]ials1 p]haps millions ( ye>s lat]4 ,?is new s$im5t may also conta9 fossils & ?us furni% an upp] limit = ! age ( ! intrusion4 ,! measur$ age ( ! intrusive rock ?us c be us$ to set upp] & l[] limits on ! absolute ages ( ! two s$im5ts4 ,if we are lucky1 ! two s$im5ts w bracket a relatively %ort int]val1 mak+ our measurem5t q precise4 ,illu/ration3 ,idealiz$ sket* ( a bracket$ intrusive4 ,! igne\s 7molt57 rock mu/ be y\ng] ?an ! s$im5t>y rock 7,a7 x intrudes1 & old] ?an ! rock 7,b7 t ov]lies x4 ,! relative age ( ! s$im5t>y b$s is kn[n f _! fossils4 ,illu/ration3 ,facsimile repr9t ( ! fam\s "t scale propos$ by ,ar?ur ,holmes 9 #aiei4 ,"t-scale 9 millions ( ye>s ,,p]iods ,s9ce beg9n+ ( p]iod ,duration ( p]iod ,,plei/oc5e ca #a 4444 ca #a 4444 ,,plioc5e #aj 4444 #aa 4444 ,,mioc5e #ad 4444 #be 4444 ,,oligoc5e #ae 4444 #dj 4444 ,,eoc5e #bj 4444 #fj 4444 ,,paleoc5e #aj 4444 #gj #b 4444 ,upp] ,,cretace\s #fe ,l[] 4444 #ace #e 4444 ,upp] ,,jurassic #de ,mid4 ,l[] 4444 #ahj #e 4444 ,,triassic #de 4444 #bbe #e 4444 ,,p]mian #de 4444 #bgj #e 4444 ,upp] ,,c>bonif]\s #hj ,l[] 4444 #cej #aj 4444 ,upp] ,,devonian #ej ,l[] 4444 #djj #aj 4444 ,,silurian #dj 4444 #ddj #aj 4444 ,,ordovician #fj 4444 #ejj #ae 4444 ,,cambrian #ajj 4444 #fjj #bj 4444 ,us+ measurem5ts made 9 _m laboratories1 & int]polat+ betwe5 !m by us+ ! relative ?icknesses ( s$im5ts1 ! great ,briti% geologi/1 ,ar?ur ,holmes1 e/abli%$ ! "t scale t is 9 g5]al use today4 ,8 orig9al scale is %[n on ! prec$+ page4 ,small *anges c be expect$ to be made 9 ?is scale f "t to "t1 b major alt]ations are n likely1 except p]haps 9 ! ,cambrian ,epo* :]e ! pres5t data are unreliable because !y are n complete4 7,a scale %[+ ! epo*s or p]iods z (t5 giv5 n[ is on page #d47 ,precambrian ,/ratigraphy ,s f> we h talk$ only ab\t rocks t are ( ! ,cambrian ,epo* or y\ng]--rocks t may conta9 fossils4 ,yet !re are va/ areas 7mo/ ( ,canada1 = example7 t are cov]$ ) rocks old] ?an ! ,cambrian =mation4 ,"s ,precambrian fossils h be5 f\nd1 b !y are s r>e t !y are useless = dat+ ! /rata conta9+ !m4 ,long-range correlation ( ,precambrian rocks mu/ rely on nucle> measurem5ts4 ,!re=e x has be5 only 9 ! la/ doz5 or s ye>s t "s ord] c\ld be e/abli%$ = ! ,precambrian rock sequ5ces4 ,! elaborate ,precambrian /ratigraphies 7arrangem5ts ( /rata 9 sequ5ce7 propos$ 9 ! pa/1 mo/ ( !m bas$ on sup]ficial simil>ities ( ! rocks 9 "o place to ^? 9 ano!r place1 n[ h be5 dra/ically alt]$ & 9 "s cases completely ov]turn$ by nucle> measurem5ts4 ,we are /ill f> f und]/&+ ! sequ5ce ( all ! ev5ts 9 t va/ span ( "t we call ! ,precambrian4 ,_m ?\s&s ( nucle> age det]m9ations w h to be made to light5 ! d>k corn]s ( our ignorance4 ,illu/ration3 ,fold$ /rata ( ,precambrian rocks1 includ+ lime/ones & %ales1 9 ,glaci] ,national ,p>k1 ,montana4 ,,& ,,:]e ,,d ,,we ,,g ,,f ,,"h8 ,p]haps we mu/ fir/ realize t we really hav5't come v f> yet4 ,grant$ t ! age ( rocks 9 _m p>ts ( ! _w is n[ sudd5ly kn[n--& t ?is 0 a total my/]y "s doz5 ye>s ago4 ,grant$ t enorm\s /rides =w>d h be5 made4 ,x's only a beg9n+4 ,va/ areas ( ! _w are /ill geologically unexplor$4 ,! geologic "t scale is /ill fragm5t>y & crude4 ,?\s&s ( important geologic que/ions rema9 to be def9$1 explor$1 & answ]$ by nucle> age det]m9ation4 ,&--z is inevitable 9 sci5ce--_m ( !m w lead to new que/ions4 ,x is app>5t t dat+ te*niques h b>ely begun to be us$ & und]/ood by geologi/s4 ,b ap>t f geologic "w1 :at else is 9 /ore8 ,x is difficult to pr$ict1 b probably ! mo/ important advance 9 ! next decade or two w come :5 we obta9 samples ( rock f ! moon4 ,w !re be "y rocks !re or w !y all be #deej million ye>s old8 ,or w !y p]haps be "s o!r age8 ,! *emical composition & nucle> ages ( ! fir/ moon samples w probably be ! mo/ important in=mation we c hope to obta9 f !m4 ,^! results f ! moon w contribute enorm\sly to our und]/&+ ( ! processes t =m$ ! e>?1 made ! cont95ts1 & det]m9$ ! major features ( our _w4 ,we h a long way to g4 ,,gloss>y ,,aeon ,"o billion 7#aj7 ye>s4 ,,alpha ,,decay ,radioactive decay ) emission ( an alpha p>ticle4 ,,alpha ,,p>ticle ,ess5tially ! nucleus ( helium1 compos$ ( two neutrons & two protons ) d\ble positive *>ge4 ,,antico9cid5ce ,,r+ ,a r+ ( c\nt]s connect$ to exclude outside radiation4 ,,backgr\nd ,,c\nt ,! numb] ( impulses p] unit "t regi/]$ on a c\nt+ in/rum5t :5 no sample is pres5t4 ,,beta ,,decay ,radioactive decay ) emission ( a beta p>ticle4 ,,beta ,,p>ticle ,an electron emitt$ by a nucleus4 ,,bracket$ ,,intrusive ,igne\s rock ext5d+ into s$im5t>y rocks t are datable by _! fossils4 ,,clos$ ,,sy/em ,a sy/em 9 :i* ! p>5t mat]ial radioactively decays into its daught] products & no?+ is add$ or remov$4 ,,common 7/rontium1 lead1 etc47 ,! ord9>y elem5t pres5t 9 nature at any "o "t z di/+ui%$ f t produc$ by radioactive decay4 ,,concordia ,,analysis ,a ma!matical te*nique to det]m9e graphically ! age ( a mat]ial conta9+ radiog5ic lead by comp>+ its uranium-to-lead ratio ) ! simil> ratio 9 a clos$ uranium-lead sy/em4 ,,contact ,,metamorphism ,a metamorphism g5etically relat$ to ! intrusion ( molt5 masses ( rock & tak+ place at or ne> ! contact4 ,,cosmic ,,rays ,high-en]gy p>ticles mov+ 9 our galaxy4 ,,cry/al ,a p]iodic or regul>ly repeat+ arrangem5t ( atoms1 =m$ f a s+le elem5t or comp\nd4 ,,daught] ,a nuclide =m$ f ! radioactive decay ( ano!r nuclide4 ,,decay ,,con/ant ,! numb] ( atoms decay+ p] atom p] unit ( "t 7#j4fic_/;half-life74 ,,electron ,,capture ,a nucle> process 9 :i* ! nucleus ( an atom captures an electron f "o ( ! inn] %ells4 ,,electrons ,elem5t>y p>ticles ) a unit negative electrical *>ge & a mass #a_/ahcg t ( ! proton1 or #i4ab #aj gram4 ,electrons surr\nd ! atom's positively *>g$ nucleus & det]m9e ! atom's *emical prop]ties4 ,,gamma ,,rays ,electromagnetic radiation f an atomic nucleus4 ,,geig] ,,c\nt]s ,in/rum5ts t c\nt pulses produc$ by radioactivity1 consi/+ ( a c\nt+ tube ) a c5tral wire anode1 usually fill$ ) a mixture ( argon & organic vapor4 ,,half-,,life ,! "t x takes = half ! atoms 9 a radioactive sub/ance to decay4 ,,ion ,an atom or molecule t has lo/ or ga9$ "o or m electrons & is ?us electrically *>g$4 ,,isotope ,,dilution ,an analytical te*nique involv+ addition ( a kn[n am\nt ( an isotopic mixture ( abnormal composition to ! unkn[n am\nt ( an elem5t ( normal or kn[n isotopic composition4 ,,isotopes ,nuclides ( ! same atomic numb] b diff]5t atomic weight4 ,isotopes ( a giv5 elem5t h an id5tical numb] ( protons b diff]5t numb]s ( neutrons 9 _! nuclei4 ,,law ,,( ,,sup]position ,/atem5t t ov]ly+ /rata mu/ be y\ng] ?an und]ly+ /rata if !re has be5 no inv]sion4 ,,mass ,,spectromet] ,an in/rum5t = sep>ation & measurem5t ( isotopes by _! mass4 ,,net ,,c\nt+ ,,rate ,sample c\nt+ rate m9us backgr\nd c\nt+ rate4 ,,neutrons ,elem5t>y p>ticles 9 ! nucleus hav+ no electric *>ge & ! mass ( "o atomic mass unit4 ,,nuclide ,a species ( atom *>act]iz$ by ! con/itution ( its nucleus4 ,,orig9al 7/rontium1 lead1 etc47 ,common /rontium1 lead1 etc41 tak5 into a sy/em at ! "t ( its =mation4 ,,paleontology ,! /udy ( fossil rema9s4 ,,p>5t ,! radioactive elem5t f :i* a daught] nuclide is produc$ by radioactive decay4 ,,plumbology ,! /udy ( ! uranium & ?orium-lead decay sy/ems4 ,! "n is d]iv$ f ! ,lat9 "n = lead1 plumbum4 ,,primordial ,pres5t at ! "t ( ! =mation ( ! e>?4 ,,proportional ,,c\nt] ,an in/rum5t = detect+ radiation by produc+ pulses ( electrical *>ge t are proportional to ! en]gy ( ! radiation be+ measur$4 ,! design p]mits use ( radiation ( a desir$ en]gy level 7)9 limits71 & discrim9ation aga9/ o!r radiation1 especially backgr\nd radiation4 ,,protons ,elem5t>y p>ticles ) a s+le positive electrical *>ge & a mass approximately #ahcg times t ( ! electron4 ,! atomic numb] ( an atom is equal to ! numb] ( protons 9 its nucleus4 ,,radioactive ,,decay ,! *ange ( "o nuclide to ano!r by ! emission ( *>g$ p>ticles f ! nucleus ( its atom4 ,,radioactivity ,! prop]ty ( "s nuclides to decay by !mselves into o!rs4 ,,radiog5ic ,=m$ z ! result ( radioactive decay4 ,,r>e ,,e>? ,any ( ! elem5ts f atomic numb] #eg 7lan?anum7 to #ga 7lutetium74 ,,sample ,,c\nt] ,an in/rum5t into :i* a sample ( mat]ial c be plac$ to h its radiation measur$4 ,,secul> ,,equilibrium ,! production ( a radioactive sub/ance at a rate equal to its decay4 ,,specific ,,activity ,! numb] ( atoms decay+ p] unit "t p] unit weight ( ! total am\nt be+ te/$4 ,,spike ,a kn[n am\nt ( an elem5t ( unusual isotopic composition us$ 9 isotope-dilution analysis4 ,,/ati/ical ,,error ,! error associat$ ) nucle> measurem5ts & aris+ f ! r&om di/ribution ( nucle> ev5ts4 ,,/rata ,plural ( /ratum4 ,a %eet or mass ( s$im5t>y rock 7=m$ by deposits ( s$im5ts1 z f anci5t seas7 ( "o k9d1 usually 9 lay]s betwe5 b$s or lay]s ( o!r k9ds4 ,,app5dix ,radioactive ,decay ,:5 a radioactive nucleus dis9tegrates or decays1 ! resultant rema9+ nucleus may /ill be radioactive1 & soon] or lat] x also w dis9tegrate & become /ill ano!r k9d ( atom4 ,?is process cont9ues ?r\gh a s]ies ( di/9ct /eps until a /able atom--"o t is n radioactive--is =m$4 ,all natural radioactivity 9 ! heavy elem5ts proce$s by su* a s]ies ( /eps1 & ! s]ies f9ally ends ) a /able =m ( lead z its end product4 ,9 o!r words1 any naturally radioactive heavy elem5t ev5tually becomes nonradioactive lead4 ,! nucleus ( e atom 7except hydrog57 conta9s "o or m neutrons & "o or m protons4 ,! in/ability ( ! nuclei ( ! heavy atoms is relat$ to ! ratio ( ! numb] ( neutrons to ! numb] ( protons 9 ! nuclei4 ,radioactive decay is1 9 fact1 a way ( adju/+ ^! ratios4 ,! adju/m5t c occur 9 v>i\s ways4 ,! mo/ common is ! emission ( alpha p>ticles or beta p>ticles4 ,an alpha p>ticle is id5tical ) ! nucleus ( a helium atom & has two neutrons & two protons bundl$ toge!r4 ,loss ( an alpha p>ticle f a nucleus l[]s ! mass numb] 7! total ( protons & neutrons7 ( ! p>5t nucleus by f\r & ! atomic numb] 7! numb] ( protons7 by two2 ! numb] ( neutrons also is r$uc$ by two4 ,a beta p>ticle is an electron & has a negative electric *>ge4 ,:5 a beta p>ticle is emitt$ f a nucleus1 ! nucleus is *ang$ s t x has "o m proton 7:i* has a positive *>ge7 & "o less neutron 7:i* has no *>ge72 9 effect1 a neutron has *ang$ into a proton z ! nucleus lo/ a negative *>ge4 ,beta decay occurs 9 nuclei ) a great] proportion ( neutrons ?an is normal = ! numb] ( protons4 ,s9ce beta emission increases ! proportion ( protons1 ! process raises ! atomic numb] ( ! p>5t nucleus by "o & leaves ! mass numb] ! same4 ,gamma rays are a =m ( electromagnetic radiation4 ,!y are emitt$ :5 a nucleus %ifts f "o en]gy /ate to a l[] en]gy /ate--! en]gy diff]5ce em]g+ z ! gamma radiation4 ,gamma emission (t5 accompanies alpha or beta emission1 b ! production ( gamma rays does n itself alt] ! atomic numb] nor ! mass numb] ( ! p>5t4 ,nuclei also c decay by emission ( a positron1 :i* is a positively *>g$ electron4 ,:5 ?is occurs1 ! new nucleus has "o m neutron & "o less proton ?an its p>5t2 9 effect a proton has become a neutron z ! nucleus loses a positive *>ge4 ,positrons usually are emitt$ by nuclei t h a great] proportion ( protons ?an is normal = ! numb] ( neutrons4 ,ano!r process--int]nal electron conv]sion--sometimes occurs 9 connection ) gamma-ray emission1 usually 9 heavy elem5ts :5 ! gamma-ray en]gy is l[4 ,in/ead ( be+ emitt$ directly1 ! gamma ray /rikes an orbital electron1 knock+ ! electron out ( ! atom2 ! gamma ray !n disappe>s4 ,ano!r electron jumps into ! 8hole0 9 ! orbit f :i* ! fir/ electron 0 emitt$1 & ?is jump--f a high] to a l[] en]gy level--results 9 ! emission ( an ,x ray 7:i* is simil> to a gamma ray1 b orig9ates 9 ! electron orbit region ( ! atom1 n 9 ! nucleus74 ,f9ally1 a nucleus may be alt]$ by electron capture4 ,9 a nucleus ) a l[ ratio ( neutrons to protons1 ! nucleus captures "o ( its own orbital electrons4 ,?is imm$iately comb9es ) a proton to =m a new neutron & emit a neutr9o 7a high-en]gy p>ticle ) nei!r mass nor *>ge74 ,! process increases ! neutron-to-proton ratio ( ! nucleus2 ! daught] has ! same mass numb] z ! p>5t1 b has an atomic numb] "o less ?an ! p>5t4 ,!re are ?ree s]ies by :i* naturally radioactive nuclei decay to /able ones3 ,! ,uranium ,s]ies1 ! ,?orium ,s]ies1 & ! ,act9ium ,s]ies4 ,man-made radioactive nuclei decay simil>ly1 ) bismu? z ! end product1 via ! ,neptunium ,s]ies4 ,^! c be illu/rat$ 9 tabul> =m & diagrammatically4 ,! ,act9ium ,s]ies 7,uranium-#bce ,s]ies71 = example1 proce$s l ?is3 ,,! ,,uranium-#bce ,,s]ies ,elem5t ,symbol ,radiation ,emitt$ ,half-life ,uranium ,u #g4ac #aj ye>s ,?orium ,? #be4f h\rs ,protact9ium ,pa #c4be #aj ye>s ,act9ium#af ,ac 7#ih4h7 & 7#a4b7 #ba4b ye>s ,?orium ,? #ah4ag days ,francium ,fr #bb m9utes ,radium ,ra #aa4g days ,radon ,rn #d4j seconds ,polonium#af ,po 7#ajj7 & 7#e #a4hc #aj second #aj7 ,lead ,pb #cf4a m9utes ,a/at9e ,at #aj second ,bismu?#af ,bi 7#ii4g7 & 7#j4c7 #b4ae m9utes ,polonium ,po #j4be second ,?allium ,tl #d4gh m9utes ,lead ,pb -- ,/able ,illu/ration3 ,! ,uranium-#bce ,s]ies ,! ,uranium 7,uranium-#bch7 ,s]ies proce$s l ?is3 ,,! ,,uranium-#bch ,,s]ies ,elem5t ,symbol ,radiation ,half-life ,uranium ,u #d4ea #aj ye>s ,?orium ,? #bd4a days ,protact9ium#ag ,pa #a4ah m9utes ,uranium ,u #b4dh #aj ye>s ,?orium ,? #g4f #aj ye>s ,radium ,ra #a4fb #aj ye>s ,radon ,rn #c4hb days ,polonium#ah ,po 7#ii4ih7 & #c4je m9utes 7#j4jb7 ,lead ,pb #bf4h m9utes ,a/at9e ,at #a4c seconds ,bismu?#ah ,bi 7#ii4if7 & #ai4g m9utes 7#j4jd7 ,polonium ,po #a4f #aj second ,?allium ,tl #a4cb m9utes ,lead ,pb #bb ye>s ,bismu?#ah ,bi 7#ajj7 & 7#b #e4j days #aj7 ,polonium ,po #ach4d days ,?allium ,tl #d4cj m9utes ,lead ,pb 444 ,/able ,illu/ration3 ,! ,uranium-#bch ,s]ies ,,sugge/$ ,,ref]5ces ,books ,h[ ,old ,is ! ,e>?81 ,patrick ,m4 ,hurley1 ,d\bl$ay ,company1 ,inc41 ,g>d5 ,city1 ,new ,york1 #aiei1 #afj pp41 #a4be4 ,radioc>bon ,dat+ 7second edition71 ,will>d ,f4 ,libby1 ,univ]sity ( ,*icago ,press1 ,*icago1 ,ill9ois1 #aiee1 #age pp41 #e4jj 7h>dback72 #a4ie 7pap]back74 ,! ,bir? & ,dea? ( ! ,sun1 ,george ,gam[1 ,! ,vik+ ,press1 ,new ,york1 #aidi1 #bch pp41 #d4ge 7out ( pr9t b available ?r\gh libr>ies71 #j4fj 7pap]back7 f ! ,new ,am]ican ,libr>y ( ,_w ,lit]ature1 ,inc41 ,new ,york4 ,inside ! ,nucleus1 ,irv+ ,adl]1 ,! ,john ,day ,company1 ,inc41 ,new ,york1 #aifc1 #aia pp41 #d4ie 7h>dback72 #j4fj 7pap]back7 f ! ,new ,am]ican ,libr>y ( ,_w ,lit]ature1 ,inc41 ,new ,york4 ,ages ( ,rocks1 ,planets1 & ,/>s1 ,h5ry ,faul1 ,mc,graw-,hill ,book ,company1 ,new ,york1 #aiff1 #aji pp41 #b4de4 ,pr9ciples ( ,geo*emi/ry 7second edition71 ,brian ,mason1 ,john ,wiley ,sons1 ,inc41 ,new ,york1 #aieh1 #caj pp41 #g4ej4 7,new edition due 9 #aifg47 ,potassium ,argon ,dat+1 ,j4 ,h4 ,zahr+] & ,o4 ,a4 ,s*aeff]1 ,spr+]-,v]lag ,new ,york1 ,inc41 ,new ,york1 #aiff1 #bej pp41 #ab4ej4 ,articles ,a ,clock = ! ,ages3 ,potassium ,argon1 ,g>niss ,h4 ,curtis1 ,national ,geographic ,magaz9e1 #abj3 #eij 7,octob] #aifa74 ,explor+ #a1gej1jjj ,ye>s into ,man's ,pa/1 ,l4 ,s4 ,b4 ,leakey1 ,national ,geographic ,magaz9e1 #abj3 #efd 7,octob] #aifa74 ,five-,billion-,ye> ,clock1 ,patrick ,m4 ,hurley1 ,saturday ,ev5+ ,po/1 #bcd3 #bf 7,m>* #ah1 #aifa74 ,geologic ,"t ,scale1 ,j4 ,laur5ce ,kulp1 ,sci5ce1 #acc3 #aaje 7,april #ad1 #aifa74 ,geology1 ,reg9ald ,a4 ,daly1 ,sci5tific ,am]ican1 #ahc3 #cf 7,septemb] #aiej74 ,tracks ( ,*>g$ ,p>ticles 9 ,solids1 ,r4 ,l4 ,fleis*]1 ,p4 ,b4 ,price1 & ,r4 ,m4 ,walk]1 ,sci5ce1 #adi3 #chc 7,july #bc1 #aife74 ,h[ ,old ,is ,x81 ,lyman ,j4 ,briggs & ,k5ne? ,f4 ,weav]1 ,national ,geographic ,magaz9e1 #aad3 #bcd 7,augu/ #aieh74 ,mov+ ,picture ( ! ,la/ ,ice ,age1 ,ri*>d ,fo/] ,fl9t1 ,natural ,hi/ory1 #ff3 #ahh 7,april #aieg74 ,mod]n ,me?ods = ,measurem5t ( ,geologic ,"t1 ,e4 ,j4 ,zell]1 ,m9]al ,in=mation ,s]vice1 #ah3 #i 7,janu>y #aife74 ,s+le copies are #j4aj f ,division ( ,m9es & ,geology1 ,f]ry-,build+1 ,san ,francisco1 ,cali=nia #idaaa4 ,flut$ ,projectile ,po9ts3 ,_! ,age & ,disp]sion1 ,c4 ,vance ,haynes1 ,jr41 ,sci5ce1 #ade3 #adjh 7,septemb] #be1 #aifd74 ,unravel+ ! ,age ( ,e>? & ,man1 ,e4 ,l4 ,simons1 ,natural ,hi/ory1 #gf3 #eb 7,febru>y #aifg74 ,radioc>bon ,dat+ & ,ar*eology 9 ,nor? ,am]ica1 ,f4 ,johnson1 ,sci5ce1 #aee3 #afe 7,janu>y #ac1 #aifg74 ,fission-track ,dat+ ( ,b$ ,i1 ,olduvai ,gorge1 ,r4 ,l4 ,fleis*] & o!rs1 ,sci5ce1 #adf3 #gb 7,april #b1 #aife74 ,lead ,isotopes & ! ,age ( ! ,e>?1 ,g4 ,r4 ,tilton & ,r4 ,h4 ,/eig]1 ,sci5ce1 #aej3 #ahje 7,decemb] #ca1 #aife74 ,/rontium-,rubidium ,age ( an ,iron ,meteorite1 ,g4 ,j4 ,wass]burg & o!rs1 ,sci5ce1 #aej3 #ahad 7,decemb] #ca1 #aife74 ,illu/ration3 ,,! ,,cov] ,u4 ,s4 ,geological ,survey sci5ti/s prep>e acetyl5e gas1 made f ! c>bon-#ad 9 a geological specim51 9 a vacuum l9e4 ,?is gas w be f$ into a proportional c\nt] to det]m9e ! age ( ! specim5 by its ,c c\nt4 7,see 8,c>bon-#ad ,c\nt+0 beg9n+ on page #ab47 ,illu/ration3 ,,! ,,au?or ,geophysici/ ,h5ry ,faul1 an au?ority on nucle> dat+1 is pr(essor ( ,geophysics & *airman ( ! ,dep>tm5t ( ,geology at ! ,univ]sity ( ,p5nsylvania1 ,philadelphia4 ,he holds a doctoral degree f ! ,massa*usetts ,in/itute ( ,te*nology1 & has taught at ! ,univ]sities ( ,/rasb\rg & ,b]n 9 ,europe4 ,dr4 ,faul 0 a geophysici/ ) ! ,manhattan ,project dur+ ,_w ,w> ,,ii1 & 0 =m]ly *ief ( ! ,radiation ,laboratory1 ,u4 ,s4 ,geological ,survey1 ,d5v]1 ,colorado4 ,= _m ye>s he 0 engag$ 9 geological age det]m9ation "w ) ! ,geological ,survey & ! ,c>negie ,in/itution ( ,wa%+ton 9 ,wa%+ton1 ,d4 ,c4 ,,photo ,,cr$its ,frontispiece c\rtesy ,an?ropology ,dep>tm5t1 ,s\!rn ,me?odi/ ,univ]sity 7,,smu7 ,cov] photo c\rtesy ,u4 ,s4 ,geological ,survey 7,,usgs7 ,page #aa ,,usgs #ab ,,usgs #ad1 #af1 #ag ,will>d ,f4 ,libby #ah ,univ]sity ( ,arizona #ba ,massa*usetts ,in/itute ( ,te*nology #bb ,graduate ,rese>* ,c5t] ( ! ,s\?we/ #bc ,graduate ,rese>* ,c5t] ( ! ,s\?we/ #be ,rob]t ,l4 ,fleis*] #bf ,p]k9-,elm] ,corporation #cj ,univ]sity ( ,texas #cb ,graduate ,rese>* ,c5t] ( ! ,s\?we/ #cf ,massa*usetts ,in/itute ( ,te*nology #dj ,des ,b>tlett1 ,arm& ,d5is ,productions #dc ,an?ropology ,dep>tm5t1 ,,smu #dd ,,usgs #dg ,,usgs #ei ,au?or's photo c\rtesy ,graduate ,rese>* ,c5t] ( ! ,s\?we/ ,footnotes #a,words appe>+ 9 ,,small ,,capital ,,lett]s are def9$ 9 ! ,gloss>y beg9n+ on page #di4 #b,! process ( natural radioactive decay is describ$ 9 ! ,app5dix beg9n+ on page #eb4 #c,! ,u4 ,s4 ,w> ,dep>tm5t program dur+ ,_w ,w> ,,ii t develop$ ! fir/ nucle> weapons4 #d;,drawn to scale1 ! :ole age ( man is repres5t$ by less ?an ! wid? ( ! l9e4 #e;,= m in=mation on ! /ructure ( atoms1 see ,our ,atomic ,_w1 a companion booklet 9 ?is s]ies4 #f;,f ! ,*>t ( ! ,nuclides1 prep>$ by ,david ,t4 ,goldman1 ,knolls ,atomic ,p[] ,laboratory1 ,augu/ #aifd4 #g,?is decay process proce$s 9 a s]ies ( /eps1 dur+ :i* #f alpha p>ticles & #d beta p>ticles are emitt$4 7,see ,app5dix47 #h,nam$ aft] _! creator1 ,john ,napi]1 a ,scotti% ma!matician 7#aeej-afag71 :o also inv5t$ ! decimal po9t4 #i;,x is difficult to det]m9e ! half-life ( ,c exactly4 ,9 ! e>ly days ( ,c dat+1 9 ord] n to delay cont9u$ "w1 an arbitr>y value ( #eefh ye>s 0 *os5 & ?is value is /ill us$ 9 calculations4 #aj,?is means t uranium decays ?r\gh successive /eps 9 :i* ! entire s]ies emits eight alpha p>ticles4 7,see ,app5dix47 #aa,rememb]1 ?is enorm\s p]iod ( "t is a measure ( ! rate ( spontane\s fission1 n ( ! age ( ,u4 #ab,! rh5ium-osmium s*eme is %[n bel[ ! dott$ l9e because ! me?od is /ill 9 an e>ly exp]im5tal /age & its g5]al utility is n yet e/abli%$4 #ac;,= m on ?is family ( elem5ts1 see ,r>e ,e>?s1 ,! ,frat]nal ,fifte51 a companion booklet 9 ?is s]ies4 #ad;,= a full] explanation ( ! fission process1 see ,our ,atomic ,_w1 ano!r booklet 9 ?is s]ies4 #ae,neutrons t h _h _! spe$ r$uc$ by pass+ ?r\gh a mod]ator 7graphite1 = example7 :i* is built into e reactor to accompli% ?is v ?+4 ,= m ab\t h[ ?is is done1 see ,nucle> ,reactors & ,rese>* ,reactors1 companion booklets 9 ?is s]ies4 #af,note t "s radionuclides sometimes decay by "o me?od1 sometimes by ano!r4 ,= example1 #ih4h ( ! nuclei ( act9ium-#bbg emit a beta p>ticle to =m ?orium-#bbg2 ! rema9+ #a4b emit an alpha p>ticle to =m francium-#bbc2 bo? ( ^! daught] products decay to radium-#bbc4 #ag,"s ( ! protact9ium 7#j4ab7 *anges by an int]m$iate /ep1 kn[n z isom]ic transition1 9 :i* its nucleus %ifts to a l[] en]gy /ate4 ,! process does n alt] ! rema9+ p>5t-daught] progression 9 ! s]ies4 #ah,und]goes bo? alpha & beta decay1 9 def9ite proportion ( decay ev5ts1 z %[n4 ,?is booklet is "o ( ! 8,und]/&+ ! ,atom0 ,s]ies4 ,comm5ts are invit$ on ?is booklet & o!rs 9 ! s]ies2 please s5d !m to ! ,division ( ,te*nical ,in=mation1 ,u4 ,s4 ,atomic ,en]gy ,commission1 ,wa%+ton1 ,d4 ,c4 #bjede4 ,publi%$ z "p ( ! ,,aec's educational assi/ance program1 ! s]ies includes ^! titles3 ,accel]ators ,animals 9 ,atomic ,rese>* ,atomic ,fuel ,atomic ,p[] ,safety ,atoms at ! ,sci5ce ,fair ,atoms 9 ,agriculture ,atoms1 ,nature1 & ,man ,c>e]s 9 ,atomic ,en]gy ,comput]s ,controll$ ,nucle> ,fusion ,cryog5ics1 ,! ,uncommon ,cold ,direct ,conv]sion ( ,en]gy ,fall\t ,f ,nucle> ,te/s ,food ,pres]vation by ,irradiation ,g5etic ,effects ( ,radiation ,index to ! ,,uas ,s]ies ,las]s ,micro/ructure ( ,matt] ,neutron ,activation ,analysis ,nonde/ructive ,te/+ ,nucle> ,clocks ,nucle> ,en]gy = ,desalt+ ,nucle> ,p[] & ,m]*ant ,%ipp+ ,nucle> ,p[] ,plants ,nucle> ,propulsion = ,space ,nucle> ,reactors ,nucle> ,t]ms1 ,a ,brief ,gloss>y ,our ,atomic ,_w ,pl[%>e ,plutonium ,p[] f ,radioisotopes ,p[] ,reactors 9 ,small ,packages ,radioactive ,wa/es ,radioisotopes & ,life ,processes ,radioisotopes 9 ,indu/ry ,radioisotopes 9 ,m$ic9e ,r>e ,e>?s ,read+ ,res\rces 9 ,atomic ,en]gy ,rese>* ,reactors ,,snap1 ,nucle> ,space ,reactors ,s\rces ( ,nucle> ,fuel ,space ,radiation ,syn!tic ,transuranium ,elem5ts ,! ,atom & ! ,ocean ,! ,*emi/ry ( ! ,noble ,gases ,! ,fir/ ,reactor ,:ole ,body ,c\nt]s ,y\r ,body & ,radiation ,a s+le copy ( any "o booklet1 or ( no m ?an ?ree diff]5t booklets1 may be obta9$ free by writ+ to3 ,,usaec1 ,p4,o4 ,,box #fb1 ,,oak ,,ridge1 ,,t5nessee #cghcj ,complete sets ( ! s]ies are available to s*ool & public libr>ians1 & to tea*]s :o c make !m available = ref]5ce or = use by gr\ps4 ,reque/s %\ld be made on s*ool or libr>y lett]heads & indicate ! propos$ use4 ,/ud5ts & tea*]s :o ne$ o!r mat]ial on specific aspects ( nucle> sci5ce1 or ref]5ces to o!r read+ mat]ial1 may also write to ! ,oak ,ridge address4 ,reque/s %\ld /ate ! topic ( int]e/ exactly1 & ! use int5d$4 ,9 all reque/s1 include 8,zip ,code0 9 return address4 ,pr9t$ 9 ! ,unit$ ,/ates ( ,am]ica ,,usaec ,division ( ,te*nical ,infection ,ext5sion1 ,oak ,ridge1 ,t5nessee ,transcrib]'s ,notes --,reta9$ publication in=mation f ! pr9t$ edition3 ?is e,book is public-doma9 9 ! c\ntry ( publication4 --,9 ! text v]sions only1 text 9 italics is delimit$ by und]scores4 --,9 ! text v]sions only1 sup]script text is prec$$ by c>et4 --,9 ! text v]sions only1 subscript text is prec$$ by und]score4