,,h[ ,,old ,,is ,,x8                    
,,! ,,/ory ,,( ,,dat+ ,,9 ,,ar*aeology  
,,museum ,,( ,,new ,,mexico ,,press     
,,popul> ,,s]ies ,,pamphlet ,,no4 #b    
,,h[ ,,old ,,is ,,x8                    
,,dat+ ,,9 ,,ar*aeology                 
by ,james ,s*o5wett]      ,!re is a :ole
 field ( sci5ce devot$ to ! inv5tion &  
developm5t ( dat+ me?ods--or 8clocks0 z 
we may ?9k ( !m4 ,x is  call$           
geo*ronology1 ! sci5ce ( dat+ ev5ts4    
,!re are  relatively few geo*ronologi/s1
 sci5ti/s tra9$ 9 ! use ( all  k9ds (   
dat+ me?ods & 9 ! !ories ^u :i* ^!      
me?ods are  bas$4    ,geo*ronologi/s    
tell u t !re are two major types (      
clocks3 ^?  t tick at an absolute rate (
 spe$ :i* c be measur$1 & ^?  :i* tick  
only once 9 a :ile4 ,a clock ( ! fir/   
type yields :at  is call$ an absolute   
date1 reveal+ ! numb] ( h\rs1 days1     
ye>s1 c5turies or mill5nia s9ce an ev5t 
occurr$4 ,a clock ( !  second type      
yields :at is call$ a relative date1    
plac+ an ev5t z  be=e or aft] ano!r     

ev5t1 b does n tell u exactly h[ f> !y  
are ap>t 9 "t nor h[ long ago !y        
occurr$4    ,dep5d+ ^u h[ accurate 8    
date mu/ be to solve ! problem he has   
set = himself1 ! ar*aeologi/ w select   
absolute or relative  dat+ me?ods4 ,(t51
 ( c\rse1 ! type ( clock he wi%es to use
 is  n available1 & he mu/ use ! next   
be/ type4 ,probably he w try  to use a  
numb] ( clocks ( diff]5t k9ds on !      
problem s9ce ea*  clock w act z a *eck  
on ! o!rs4    ,! absolute clock utiliz$ 
mo/ widely 9 ar*aeology is ! hi/orical  
record4 ,m5 h us$ cal5d>s = a long "t1 &
 h (t5 left  records ) writt5 dates4 ,on
 tomb/ones at a site 9 old ,virg9ia1 on 
! p$e/als ( /atues & o!r monum5ts f     
classical ,greece &  ,rome1 on ! walls (
 ! tombs ( ,egyptian k+s1 dates are     
cle>ly  inscrib$ :i* c be relat$ to !   
sites dug into by !  ar*aeologi/s4 ,^!  
dates mu/ (t5 be recalculat$ 9 t]ms ( ! 
,*ri/ian cal5d> :i* we use4 ,mo/ cal5d>s
 9 use 9 !  ,m$it]ranean1 ! ,ne> ,ea/ & 
,*9a dur+ classical antiquity h  be5    

successfully correlat$ ) ! "o we use    
today1 & a date  inscrib$ or not$ on su*
 sites c be consid]$ 9 our own t]ms4    
,o!r cal5d>s1 su* z ^? develop$ 9 !     
anci5t cultures ( !  ,maya on ! ,yucatan
 ,p59sula1 h yet to be accurately       
correlat$ )  our own4 ,su* cal5d>s c be 
us$ on _! own t]ms ( c\rse1 & a  site   
:i* has an inscription 9 ! ,mayan cal5d>
 is kn[n to be s  _m ye>s old] or y\ng] 
?an ano!r "o ) a diff]5t date 9  t      
cal5d>4 ,we speak ( su* a situation z a 
float+ *ronology4  ,t is1 ! sequ5ce (   
ev5ts & ! numb] ( ye>s :i* sep>ate  !m  
are kn[n1 b ! dates ( ^? ev5ts 9        
absolute "t are  unkn[n4                
,illu/ration3 7uncaption$7    ,tree r+s 
af=d ano!r k9d ( absolute clock1 !      
d5drological  me?od4 ,ea* ye> a tree    
adds a gr[? r+4 ,dep5d+ on ! am\nt (    
wat] ! tree has available to x = cell   
gr[?1 ! r+ w be  wid] or n>r[]4 ,c]ta9  
trees ^: wat] requirem5ts are high live 
ne> /reams or o!r places :]e _! roots c 
tap a con/ant supply  ( wat]4 ,su*      

trees1 ref]r$ to z complac5t1 h annual  
r+s  :i* are all ( ab\t ! same wid?4    
,o!r s5sitive trees live 9  places :]e  
!y mu/ dep5d almo/ :olly on ra9fall = _!
 wat]  supply1 z on ! slopes ( hills or 
9 ! clefts ( rocks4 ,su* trees  h annual
 r+s :i* v>y 9 wid? dep5d+ ^u ! am\nt ( 
ra9  !y receive4 ,9 any giv5 area1      
especially 9 arid & semi>id  regions1 "s
 ye>s h m ra9fall ?an o!rs4 ,! s5sitive 
trees  w produce wid] r+s dur+ ye>s :5  
!re is m ra9fall &  n>r[] r+s 9 ye>s :5 
!re is less4 ,(t5 !re are p]iods ( a    
decade or s :5 all ( ! s5sitive trees w 
produce ! same  patt]n ( r+ gr[?2 =     
example1 ?ree ye>s ( n>r[ r+s1 "o  ye> (
 wide1 two m ( n>r[ & ?ree m ( wide4    
,su* a patt]n  is call$ a signature4    
,signatures are ! basis ( tree r+       
*ronologies4 ,all ! trees 9 a  region   
did n beg9 gr[+ at ! same "t ( c\rse1 b 
e "t  !re is a s]ies ( ye>s :i* w       
produce a signature1 all !  s5sitive    
trees /ill alive w h t signature4 ,let u
 say we cut  d[n a s5sitive tree 9 #aifj

 &1 by c\nt+ back ! r+s1 f9d  signatures
 at #aidj-de1 #aiaj-ad1 #ahhj-hi1       
#ahba-bg1 #agie-ahjj & #agej-eh4  ,next 
we recov] a beam f an ab&on$ ,spani%    
,mission built 9 #ahaj4  ,x happ5s to be
 f a s5sitive tree1 & we c spot !       
#agie-ahjj  & ! #agej-eh signatures ne> 
! out] r+s4 ,n[ we h two records  :i* c 
be said to be crossdat$4 ,let u assume t
 ! ,spani%  ,mission log give u         
signatures z f> back z #acej4 ,an ab&on$
 ,indian  pueblo produces a log )       
signatures crossdat+ ^? ( ! ,spani%     
,mission log & cont9u+ ! record back to 
#abej4 ,old] & old]  ar*eological sites 
w yield old] & old] signatures ) ea* log
  crossdat+ "s ( ! signatures ( y\ng]   
logs4    ,at pres5t we h a tree r+      
cal5d> = c]ta9 species ( trees  ext5d+  
back to ab\t #ajj ,b4,c4 ,?is is call$ a
 ma/] tree r+  *ronology4 ,a log f an   
ar*aeological site may conta9 only "o or
  two signatures & be1 9 itself1 a      
float+ *ronology1 b by  comp>ison ) !   
ma/] *ronology "o c det]m9e ! cutt+     

date4 ,hav+ a s]ies ( cutt+ dates = !   
con/ruction timb]s 9  an ar*aeological  
site yields ! probable dates at :i* !   
site 0  built & occupi$4                
,illu/ration3 ,diagram to ,illu/rate    
,tree ,r+ ,dat+4 ,reproduc$      by     
special p]mission f ,/all+s1 8,dat+     
,prehi/oric ,ru9s by      ,tree-,r+s40  
,c ,,?is ,,beam ,,came ,,f ,,an ,,old   
,,h\se    ,b ,,?is ,,beam ,,came ,,f ,a 
,,h\se    ,a ,,?is ,,0 ,a ,,liv+ ,,tree 
,,:5 ,,cut ,,by ,,u    ,,! ,,r+         
,,patt]ns ,,mat* ,,& ,,ov]lap ,,back    
,,into ,,"t    ,,specim5s ,,tak5 ,,f    
,,ru9s1 ,,:5 ,,mat*$ ,,& ,,ov]lapp$ ,,z 
,,indicat$1            ,,progressively  
,,ext5d ,,! ,,dat+ ,,back ,,into        
,,prehi/oric ,,times4    ,n all k9ds (  
trees c be us$ = d5dro*ronology4 ,p9e1  
fir &  p9yon are ! mo/ useful2 junip] c 
sometimes be us$4 ,oak1  cottonwood1    
will[ & o!rs are v difficult to date &  
frequ5tly  _c be us$ at all4    ,ano!r  
widely us$ absolute clock is t bas$ ^u !
 ord]ly  decomposition ( c>bon4 ,?is is 

! radioc>bon or ,c-#ad me?od (  dat+4   
,molecules ( v>i\s sub/ances are made up
 ( atoms4 ,we "k  n[ t n all atoms ( a  
sub/ance are precisely ! same4 ,we speak
  ( isotopes ( an atom4 ,to cl>ify ?is  
let u ?9k ( ! atoms (  c>bon z be+ made 
up ( a mass ( p+-pong balls4 ,"s atoms w
  h m p+-pong balls ?an o!rs1 b all w h 
en\gh & 9  ! prop] ord] to be c>bon     
atoms4 ,ea* ( ! atoms ) #ad p+-pong     
balls we %all ref] to z ! c>bon-#ad     
isotope ( c>bon4 ,!re w  be o!r isotopes
 ( c>bon atoms too4    ,! c>bon-#ad     
isotope is ab\t av]age 9 life span4 ,x  
has be5  det]m9$ t 9 any gr\p ( ,c-#ad  
isotopes half ( !m w lose two  ( _!     
p+-pong balls & become ,c-#ab isotopes 9
 #e1gcj ye>s1 plus  or m9us #dj4 ,?is is
 kn[n z ! half-life ( ! ,c-#ad isotope4 
,!  8plus or m9us #dj0 all[s =          
laboratory error 9 t]ms ( ye>s4    ,n[  
all liv+ ?+s conta9 c>bon atoms1 & "s ( 
^? atoms are  ,c-#ad isotopes4 ,! am\nt 
( ,c-#ad isotopes 9 a liv+ organism     
quickly  rea*es a /able p]c5tage aft]   

:i* !re is no increase or decrease  :ile
 ! organism is alive4 ,aft] x dies1 !   
,c-#ad supply is n  repl5i%$1 & ) !     
pass+ ( #e1gcj plus or m9us #dj ye>s1 x 
has half ! numb] ( ,c-#ad isotopes x _h 
:5 alive4 ,9 #aa1dfj plus  or m9us #hj  
ye>s1 x w h "o qu>t] z _m z x _h :5     
alive4    ,! geo*ronologi/ takes a c]ta9
 weight ( c>bon-be>+ matt] f  an        
organism :i* once liv$4 ,) simple       
*emi/ry he c det]m9e !  numb] ( c>bon   
atoms 9 ! mat]ial1 usually *>coal1 wood1
 bone or  %ell4 ,he places ! mat]ial 9 a
 *amb] equipp$ ) geig] c\nt]s  & records
 ! numb] ( ,c-#ad isotopes conv]t+ to   
,c-#ab isotopes  )9 a c]ta9 numb] ( h\rs
 or days4 ,s9ce he kn[s h[ _m c>bon     
atoms !re are 9 ! specim51 he kn[s h[ _m
 ,c-#ad isotopes !re  w\ld be if !      
specim5 7 alive4 ,he also kn[s t z !    
numb] (  ,c-#ad atoms decreases ! numb] 
( clicks on ! geig] c\nt] w  decrease   
too4 ,= example1 if !re are #b1jjj      
,c-#ad isotopes1 !  decomposition ( half
 ( ^! ov] a p]iod ( approximately #e1gcj

  ye>s w\ld regi/] #a1jjj clicks on !   
c\nt]4 ,9 ! next #e1gcj ye>  p]iod !re  
w\ld be #a1jjj isotopes left1 & only    
#ejj ( !m w\ld  decompose to regi/] z   
geig] c\nt] clicks4    ,! geo*ronologi/ 
does ! c\nt+ & analysis ( ! results &   
s5ds ! in=mation back to ! ar*aeologi/ 9
 ! =m ( !  numb] ( ye>s t h elaps$ s9ce 
! c>bon 0 "p ( a liv+  creature2 =      
example1 #a1ejj plus or m9us #aej ye>s  
,,bp 7be=e  pres5t74 ,! ar*aeologi/1    
conv]t+ ?is to ! ,*ri/ian cal5d>  9     
#aifd1 w\ld come up ) ,a4,d4 #dfd plus  
or m9us #aej ye>s4 ,:5 0  ! sample      
actually alive8 ,we don't "k exactly1 b 
/ati/ically we  h a n9ety-five p]c5t    
*ance ( be+ "r if we say sometime       
betwe5 ,a4,d4 #afd & #gfd4 ,?is clock   
ticks 9 c5turies4 ,b !  radioc>bon clock
 doesn't tick v long1 ev5 9 c5turies1   
be=e  runn+ d[n4 ,by ! "t #cj1jjj to    
#dj1jjj ye>s h gone by1 ! ,c-#ad  9 any 
sample is almo/ gone1 & !re is too      
little left to give  en\gh geig] c\nt]  
clicks unless "o is will+ to wait a     

lifetime to  record two or ?ree clicks4 
,! ,c-#ad dat+ te*nique measures "t by  
radioactive decomposition (  mat]ials4  
,!re are o!r clocks :i* dep5d on !      
*emical  decomposition ( mat]ials4 ,!   
=g]y ( ! ,piltd[n ,man fossil 0  detect$
 by a dat+ me?od :i* dep5ds on !        
decomposition ( bone  prote9 & its      
replacem5t by fluor9e4 ,fluor9e is an   
elem5t :i*  occurs naturally z a gas1 b 
:i* comb9es readily ) o!r  elem5ts to =m
 comp\nds4 ,"s ( ^! elem5ts are common 9
 bones4  ,s9ce fluor9e is "o ( nature's 
mo/ reactive elem5ts1 x t5ds to  escape 
f ! comp\nd x is 9 & to =m o!r comp\nds4
 ,z !  prote9 9 a bone decays1 x is (t5 
replac$ by fluor9e4 ,! am\nt  ( fluor9e 
9 old bones1 !n1 is expect$ to be m ?an 
9 "y  bones s9ce x has _h m "t to       
accumulate4 ,s9ce fluor9e does n        
accumulate at a con/ant rate1 x af=ds   
only a relative measure (  age4    ,9 ! 
case ( ,piltd[n1 a gr\p ( bones 0       
discov]$ at a site1 &  0 said to conta9 
^? ( "o individual :o liv$ ab\t #fj1jjj 

ye>s  ago4 ,almo/ #ajj ye>s aft] !y 7   
discov]$1 ^! bones 7 put  to ! fluor9e  
te/4 ,x 0 f\nd t 7#a7 "s ( ! bones _h   
less  fluor9e ?an o!rs1 s n all 7 ( !   
same antiquity & c\ld  n h belong$ to ! 
same individual1 7#b7 ! y\ng] bones _h z
  mu* fluor9e 9 !m z mod]n bones1 & 7#c7
 ! old] bones _h m  fluor9e 9 !m ?an    
bones kn[n to be #fj1jjj ye>s old4      
,illu/ration3 7uncaption$7    ,ano!r =m 
( absolute dat+ ( importance to         
ar*aeology is t  call$ ! v>ve me?od4    
,?is c only be utiliz$ z an absolute    
clock "u v special circum/ances h[ev]4  
,v>ves are l tree  r+s 9 a way4 ,9 a    
lake :i* is suffici5tly deep1 or at !   
edge (  a glaci]1 p>ticles ( s$im5t are 
be+ deposit$ cont9u\sly z a  sort (     
fall\t f ! wat]4 ,dur+ ! w9t]1 :5 !     
glaci]  freezes or ! d5sity ( ! wat] 9 !
 lake increases because ( !  cool]      
temp]ature1 less p>ticles are deposit$1 
& ^? :i* are  deposit$ are usually ( a  
*>act]i/ic color or texture4 ,dur+ !    
summ]1 :5 ! glaci] melts or ! lake w>ms 

up1 m & diff]5t  p>ticles are deposit$4 
,! b&s ( deposit$ s$im5t are call$      
v>ves2 e ye> two v>ves are =m$4 ,/>t+ f 
! top1 "o c  c\nt back ! numb] ( ye>s 9 
a v>ve s]ies4 ,if ! top v>ve is (  kn[n 
date su* z ! pres5t ye>1 "o has a cal5d>
 ) ea* v>ve  hav+ a kn[n date4 ,attempts
 are made to correlate "o v>ve s]ies  ) 
ano!r 9 ord] to recov] ev5 long] s]ies4 
,if !  ar*aeologi/ is lucky1 & x is n   
r>e 9 ,europe1 !re w be  mat]ials f a   
site buri$ 9 ! local v>ve sequ5ce4      
,c\nt+ back  gives an absolute age = !  
artifacts emb$d$ 9 ! site & ?us an      
approximate age = ! site4 ,! ,european  
v>ve *ronology is believ$  to ext5d back
 to ab\t #ifej ,b4,c4    ,mo/ ( ! clocks
 :i* ! ar*aeologi/ uses to produce      
relative  dates1 ! be=e-or-aft] k9d1 h z
 _! !oretical basis !  pr9ciple (       
/ratigraphy4 ,9 effect ! pr9ciple (     
/ratigraphy  assumes two ?+s3 t ! rocks 
( ! e>? are con/antly we>+  d[n by      
erosion1 & t ?+s :i* appe> to be alike  
actually are  alike & are probably m or 

less ! same age4    ,if rocks are       
con/antly we>+ d[n1 x foll[s t ! surface
 ( !  gr\nd is con/antly build+ up4 ,?us
 ! surface we walk on is a  y\ng]1 high]
 surface ?an t :i* our ance/ors walk$   
on4 ,:5 we  dig bel[ ! surface1 ^? ?+s  
we f9d :i* are at high] levels  are     
y\ng] ?an ^? :i* we f9d at l[] levels4  
,! deep] we dig1  ! old] ?+s get4       
,!re is no reason to believe t ! rate ( 
deposition on ! surface  is ! same      
ev]y:]e4 ,if we dig two feet 9 "o place 
we may be at a  level :i* is n[ five    
feet bel[ ! surface 9 ano!r location4   
,if  we f9d a p>ticul> object1 say a    
type ( pott]y1 on ! surface at  site ,a 
& ! same k9d ( pott]y five feet bel[ !  
surface at site  ,b1 we c use ! second (
 our assumptions & ma9ta9 t bo?  pieces 
are ( ! same age4 ,!n any objects f\nd  
at high] levels ?an  five feet at site  
,b are y\ng] ?an ! piece ( pott]y & are 
y\ng] ?an any?+ f\nd at site ,a4 ,?is is
 ! pr9ciple (  /ratigraphy4    ,l tree  
r+s1 objects 9 /ratigraphic sequ5ce c be

 crossdat$4  ,^! sequ5ces may be ( v>i\s
 k9ds z any object w d4  ,di/9ctive b&s 
( s$im5t1 di/9ctive artifacts1 types (  
fossils1  specific details ( *emi/ry or 
any o!r ph5om5on may be us$ )  v>y+     
am\nts ( success4 ,suppose we h ! foll[+
 sequ5ces (  objects at sites ,a & ,b3  
,illu/ration3 7uncaption$7              
,a                               ,b     
,black e>?                    ,br[n du/ 
,cali*e                     ,black e>?  
,erod$ lay]                    ,cali*e  
,cobbles                     ,yell[ silt
                ,soil                   
,br[n silt             ,br[n silt       
,erod$ lay]                             
,cobbles    ,n[ !re are "s ?+s t are    
simil> ab\t ^! two pr(iles  & o!r ?+s t 
are diff]5t4 ,bo? pr(iles conta9 lay]s (
  black e>?1 cali*e1 an erod$ lay] &    
cobbles4 ,bo? pr(iles conta9  pott]y1 & 
bo? conta9 arr[ po9ts4 ,! type ( pott]y 
9 pr(ile ,a  is ! same z t 9 pr(ile ,b1 
b 9 ,b !re is br[n du/ above !  black   
e>?4 ,9 pr(ile ,b ! br[n silt is above !

 erod$ lay]1  :ile 9 ,a x is bel[ !     
erod$ lay]4 ,9 pr(ile ,a ! arr[ po9ts  h
 diff]5t %apes ?an ! ones 9 pr(ile ,b4  
,:at we ne$ to  correlate ! sequ5ces are
 horizon m>k]s1 objects t are en\gh     
alike to be 9 ! same "t range4    ,!    
pots 9 bo? cases look ! same & are      
emb$d$ 9 ! same k9d  ( s$im5t1 ! black  
e>?4 ,!y =m "o horizon4 ,! cali*e may be
  a horizon m>k]1 b ?is is n positive   
s9ce at pr(ile ,a x is  above ! erod$   
lay]1 :ile at pr(ile ,b x is above !    
yell[ silt4  ,! erod$ lay] sits above   
cobbles at bo? pr(iles1 :i* makes !     
erod$ lay]-cobbles complex a pretty good
 horizon m>k]4 ,! br[n  silt is n a     
horizon m>k] because x is above ! erod$ 
lay] at "o  pr(ile & bel[ x at ! o!r4   
,fur!rmore1 ! arr[ po9ts :i*  x conta9s 
are n all ( ! same k9d4 ,! correlat$    
sequ5ce1 us+  ! horizon m>k]s1 mu/ be z 
%[n 9 ! accompany+ *>t4    ,!           
/ratigraphy proves t ! arr[heads 9 !    
upp] br[n silt mu/  be y\ng] ?an ^? 9 ! 
l[] br[n silt4 ,! next "t we f9d        

arr[heads ( ! types recov]$ 9 ! upp]    
br[n silt we w "k1  reg>dless ( !       
/ratigraphic sequ5ce 9 ! new locality1 t
 !y  mu/ be y\ng] ?an ! types f\nd 9 !  
l[] br[n silt1 & !y  mu/ also be old]   
?an pott]y ( ! type f\nd 9 ! black e>?4 
,we  won't "k h[ _m ye>s old !y are1 b  
we h dat$ !m 9 !  s5se t we "k !y are   
old] ?an "s ?+s & y\ng] ?an  o!rs4    ,!
 pr9ciple ( /ratigraphy is "o ( !       
ar*aeologi/'s mo/ useful  !oretical     
tools z x all[s "o site to be comp>$ )  
o!rs4 ,our  example has %[n h[ artifacts
 7pots & arr[heads 9 ?is case7 &  s$im5t
 types c be plac$ 9 /ratigraphic ord] to
 provide a clock  = ar*aeological dat+4 
,o!r objects :i* are commonly us$ z     
horizon m>k]s 9 /ratigraphic sequ5ces   
are fossils4 ,rema9s (  ext9ct animals  
are (t5 us$ to prove extreme antiquity4 
,rema9s (  plants & animals w (t5       
indicate simil>ity ( ecological         
conditions at two sites & all[ !m to be 
crossdat$4        ,illu/ration3         
7uncaption$7                            

,br[n du/                               
,black e>?                              
,cali*e                                 
,yell[ silt                             
,br[n silt                              
,erod$ lay]                             
,cobbles                                
,soil                                   
,br[n silt    ,! geologic-climatic me?od
 ( dat+ comb9es ! pr9ciple (            
/ratigraphy ) an int]pretation ( ! mean+
 ( natural  occurr5ces4 ,:5 geologi/s   
demon/rat$ t ! e>? _h rec5tly  gone     
?r\gh a p]iod :5 enorm\s glaci]s advanc$
 & retreat$  across ! nor!rn & s\!rn    
hemisph]es1 !y began to speculate on  ! 
effects ( su* conditions on ! l&scape4  
,! surface w\ld be  scrap$ d[n to b>e   
rock by ! advanc+ ice %eet4 ,:5 ! ice   
retreat$1 its load ( rocks & cobbles    
w\ld t5d to be left beh9d1  :ile !      
small] p>ticles ( dirt w\ld be flu%$    
away 9 ! riv]s  =m$ by ! melt+ ice4 ,if 
! ar*aeologi/ f\nd tools among !  b\ld]s
 & cobbles1 ^? tools %\ld date to !     

p]iod :5 !  cobble & b\ld] /ratum 0 =m$1
 ! p]iod :5 ! glaci] 0  retreat+4 ,"h ! 
geology gave clues to ! climate1 & if ! 
age  ( ! climatic ev5t 0 kn[n1 artifacts
 associat$ ) ! geology  c\ld be dat$4   
,x is ?r\gh ! geologic-climatic me?od ( 
dat+ t ar*aeologi/s  discov]$ t human   
be+s liv$ 9 s\!rn ,europe at ! m>g9 (  !
 la/ great glaci]1 & !re=e ! date ( _!  
occupation 0  on ! ord] ( #bj1jjj ye>s  
ago4    ,x is n necess>y to use !       
geologic aspect ( geologic-climatic     
dat+ if "o has o!r clues to ! climate4  
,plant & animal fossils  are clues to   
anci5t climates1 s9ce liv+ organisms h a
 t5d5cy to  live 9 climates to :i* !y   
are be/ adapt$4 ,if we f9d ! fossil     
bones ( a giraffe or an o/ri* 9 ! ,sah>a
 ,des]t1 we c conclude  t at "s "t 9 !  
pa/ ! ,sah>a 0 n a des]t b a veldt1     
s9ce giraffes & o/ri*es live 9 ! veldt  
today4 ,if /ratigraphy  all[s u to      
relate artifacts to ^? fossils1 we c    
ma9ta9 t !  mak]s ( ^? artifacts liv$ at
 ! "t ! veldt exi/$ 9 :at is  n[ !      

,sah>a area4 ,n[ if we c relate !       
fossils to a date :5  su* a climate c\ld
 h obta9$ 9 ! area1 we h a date = !     
artifacts4    ,animal fossils are       
relatively r>e1 & fossil rema9s ( plants
 :i*  c be se5 ) ! nak$ eye are ev5 r>]4
 ,b microscopic poll5  gra9s are n      
p>ticul>ly r>e 9 ! /ratigraphic sequ5ces
 (  s$im5ts1 & are directly associat$ ) 
artifacts 9 _m k9ds (  s$im5t4 ,! poll5 
( mo/ plants is protect$ by a t\gh coat 
l  t on _m se$s4 ,millions ( poll5 gra9s
 are produc$ by local  vegetation ea*   
ye>1 & a p]c5tage ( !m are buri$ 9 !    
ye>ly  accumulation ( s$im5t4 ,once !y  
are buri$1 ! t\gh out] cov]+  is        
pres]v$4        ,illu/ration3           
7uncaption$7    ,:5 poll5 gra9s are     
extract$ f _! s$im5t matrix1 !  diff]5t 
types ( plants :i* grew 9 ! area at ! "t
 !  s$im5t 0 laid d[n c be recogniz$ f !
 di/9ctive  *>act]i/ics ( _! poll5      
gra9s4 ,! poll5 analy/ has ! job  (     
int]pret+ ?is in=mation to discov] !    
nature ( !  vegetation patt]ns 9 ! pa/ &

 ! climates associat$ ) !m4  ,?r\gh dat+
 ^? climates1 ! artifacts ) :i* ! poll5 
sample 0 associat$ are dat$4    ,"s     
ar*aeological sites d n all[ dat+ by any
 ( ^! me?ods4  ,! f>m] pl[+ a field may 
pick up an arr[head & wond] h[ old  x   
is4 ,c ! ar*aeologi/ date ! arr[head8 ,!
 answ] is a  qualifi$ yes4 ,:at !       
ar*aeologi/ w try to d is give an       
educat$  guess z to ! age ( ! arr[head4 
,he might1 = example1 "k t  arr[heads ( 
t type are f\nd at a site :i* is dat$   
ab\t ,a4,d4  #ajjj by v>i\s me?ods4 ,by 
correlation1 he c\ld apply t date4      
,if ! arr[head is n ( a type :i* has be5
 reliably dat$1 !  ar*aeologi/ may rely 
^u ! me?od ( dat+ kn[n z s]iation4  ,?is
 me?od dep5ds on ! second assumption    
basic to ! pr9ciple (  /ratigraphy1 t   
simil> objects t5d to be ab\t ! same    
age4 ,!  f>m]'s arr[head may n be       
exactly l any :i* has ev] be5  discov]$1
 b x probably w be m l "s kn[n ones ?an 
o!rs4 ,obs]v+ ! g5]al /yle ( ! arr[head 
& ! way 9  :i* x is made1 ! ar*aeologi/ 

c make a pretty good e/imate (  :5 x 0  
made4    ,let u assume t ! ar*aeologi/  
goes into an unexplor$ area :]e  no     
absolute or relative dat+ te*niques are 
available4 ,!re he f9ds  a numb] ( sites
 ) pot%]ds ( types new to ar*aeology4 ,c
 he  date ^! sites8 ,aga9 he uses       
s]iation1 b ?is "t he inv]ts !  logical 
proposition4 ,if ?+s :i* look alike t5d 
to be ( ! same  age1 ?+s :i* d n look   
alike %\ld t5d to be ( diff]5t ages4    
,8 fir/ task w\ld be to sep>ate all !   
diff]5t types (  pot%]ds4 ,tak+ a       
specim5 ( ea* type1 he lays !m out 9 a  
r[4 ,if  !re is any diff]5ce 9 ! sites  
?r\gh "t1 ! /yles ( pott]y  w *ange     
correspond+ly4 ,b !re w be "s /yles :i* 
*ange  sl[ly & "s :i* w influ5ce o!rs4  
,= example1 if we 7 to  s]iate ! /yle ( 
automobile re> f5d]s = ! p]iod #aief to 
#aifd1 we w\ld obs]ve t !y began to     
spr\t tall] & tall] f9s2  !n ! size ( ! 
f9s became r$uc$ m & m4 ,"s ( !  /yle   
aspects ( pre-#aief re> f5d]s w5t along 
) ! developm5t  ( f9s & o!rs dropp$ out4

 ,"s ( ! /yle aspects :i* 7  develop$ ) 
! f9s 7 reta9$ aft] ! f9s decreas$ 9    
size4    ,s]iation ( ! design /yles on !
 pot%]ds w result 9 a s]ies  (          
developm5ts 9 /yle :i* are probably 9   
*ronological ord]4  ,broad /raight l9e  
designs may give way to mix$ broad &    
n>r[  /raight l9es1 !n to n>r[ /raight  
l9es1 !n to n>r[ wavy  l9es4 ,!         
ar*aeologi/ c\ld !n ma9ta9 t sites :i* h
  pot%]ds ) broad /raight l9es are      
sep>ate 9 "t f ^? )  %]ds hav+ n>r[ wavy
 l9es4 ,he won't "k :i* is ! old]1      
because ! sequ5ce c\ld "w ei!r way4     
,/ratigraphy or ! cultural  simil>ity   
betwe5 o!r artifacts at ! sites w       
probably resolve  ?is problem4    ,!    
read] w n[ h realiz$ t _m ( ! clocks us$
 by  ar*aeologi/s are int]relat$4       
,relative dat+ clocks su* z             
/ratigraphy1 poll5 dat+ &               
geologic-climatic dat+ are utiliz$      
toge!r :]e possible1 & all are dep5d5t  
^u ! pr9ciple (  /ratigraphy4 ,crossdat+
 is ?us ( vital importance & is         

con/antly  und]tak54 ,! ar*aeologi/     
tries to employ bo? absolute & relative 
clocks to f9d out ! age ( a site4       
,/ratigraphy yields a s]ies (  relative 
dates = artifacts )9 ! site2            
geologic-climatic &  poll5 dat+ yield a 
s]ies ( dates = types ( s$im5t & samples
  collect$ 9 association ) ^? artifacts2
 tree r+ dates yield !  absolute age ( !
 site :i* all[s ! poll51 /ratigraphic & 
geologic-climatic dates to be compreh5d$
 9 t]ms ( absolute age4  ,radioc>bon    
dates act z a *eck on ! tree r+ dates &1
 if !y  agree1 l5d support to ! poll5 & 
geologic-climatic dates4 ,!  poll5 &    
geologic-climatic dates f ! site are    
comp>$ )  simil> dates f o!r sites z    
additional *ecks4 ,s9ce ! clocks  us$ by
 ! ar*aeologi/ tick at diff]5t rates (  
spe$1 & s9ce  n all ( !m are dat+ ! same
 ?+1 ! ar*aeologi/ usually  ends ) a    
s]ies ( dates = any giv5 site4    ,new  
geo*ronological te*niques are always be+
 inv5t$ & p]fect$4  ,"h is a li/ ( "s t 
are expect$ to become available 9 ! next

  few ye>s3    #a4 ,! obsidian hydration
 me?od4 ,obsidian1 a naturally =m$      
glass1  is s con/itut$ *emically t x    
takes *emicals f its  environm5t at a   
sl[ rate4 ,z x does s1 ! outside lay]   
*anges  f transp>5t to transluc5t or    
opaque4 ,! dep? ( ! opaque  lay]1 x is  
hop$1 c be us$ z a measure ( ! am\nt (  
"t s9ce  ! surface 0 expos$4 ,z _m      
artifacts 7 made by *ipp+  obsidian to  
=m a %>p edge1 ?is me?od may reveal ! "t
 s9ce an  obsidian artifact 0 made4     
#b4 ,! !rmolum9esc5ce me?od4 ,! *emical 
prop]ties ( c]ta9  m9]als *ange :5 !    
m9]als are heat$ to high temp]atures4   
,if  !y are heat$ aga9 !y w gl[1 & !    
am\nt ( "t !y gl[  ^u reheat+ dep5ds on 
! am\nt ( "t t has elaps$ s9ce !y  7    
heat$ orig9ally4 ,z yet ! rate has n be5
 accurately  calculat$1 nor is x yet    
und]/ood :at effect diff]5t k9ds (      
soils & atmosph]es may h on ?is rate4   
,if ! me?od is prov51 x  w be invaluable
 to ar*aeology s9ce x w af=d a way (    
dat+  pott]y directly on an absolute "t 

scale4    #c4 ,! paleomagnetism me?od4  
,:5 an object conta9+ p>ticles  :i* c be
 magnetiz$ is heat$1 ! magnetic p>ticles
 l9e up  accord+ to ! e>?'s magnetic    
field4 ,:5 ! object cools1 !  p>ticles  
are trapp$ 9 ?is position4 ,we "k t !   
e>?'s  magnetic field is *angeable1 & t 
at diff]5t times x has be5  ori5t$ 9    
diff]5t directions4 ,"w is n[ 9 progress
 to det]m9e  h[ ! field has v>i$ ?r\gh  
"t & h[ successfully "o c date  mat]ials
 su* z pott]y or he>?s :i* 7 expos$ to  
high  temp]atures 9 ! pa/ by ! diff]5ce 
betwe5 ! pres5t magnetic  field & t     
trapp$ 9 ! object4                      
,museum ( ,new ,mexico ,press           
,santa ,fe    #aife                     
,illu/rations by ,m>y ,sp5c]            
& ,phyllis ,hughes                      
,transcrib]'s ,notes      --,sil5tly    
correct$ a few typos4    --,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