Problems in the Radiocarbon Dating of Bone - ACS Publications

23 Problems in the Radiocarbon Dating of Bone R. E. T A Y L O R

Downloaded by FUDAN UNIV on February 16, 2017 | http://pubs.acs.org Publication Date: January 29, 1982 | doi: 10.1021/bk-1982-0176.ch023

University of California, Department of Anthropology, Institute of Geophysics and Planetary Physics, Riverside, C A 92521

Amino acid composition data and stable isotope ratios are being evaluated as sources of information to indicate the presence of non-indigenous organics i n bone samples intended for radiocarbon analyses. The study i s being conducted i n the context of the planned C measurement of Pleistocene bone samples by high energy mass spectrometric methods. 14

The assumptions o f the radiocarbon method are w i d e l y known and understood (Table 1). Each has been the s u b j e c t o f review and comment over more than t h i r t y years o f C s t u d i e s [ 1 - 3 ] . Included i n Table 1 under the heading contextual i s an assumption sometimes not emphasized i n d i s c u s s i o n s o f the accuracy o f C determinations. I t i s essential that the f i e l d archaeologist, g e o l o g i s t o r geomorphologist document contextual r e l a t i o n s h i p s o f sample m a t e r i a l s w i t h a c l o s e l y defined c u l t u r a l o r g e o l o g i c a l event. One way i n which a r c h a e o l o g i s t s have attempted t o circumvent the danger o f p o s s i b l e m i s a s s o c i a t i o n o f sample w i t h c u l t u r a l event i s t o o b t a i n a C determination d i r e c t l y on the c u l t u r a l item i t s e l f . In c e r t a i n c o n t e x t s , however, an even more fundamen t a l question i s whether the phenomena i n question can be r e l a t e d t o human behavior a t a l l . T h i s , f o r example, i s one o f the b a s i c questions t h a t continues t o a r i s e i n d i s c u s s i o n s concerning the a n t i q u i t y o f Homo sapiens i n the Western Hemisphere. For more than a century, a r c h a e o l o g i s t s and others have debated the v a l i d i t y o f proposed evidence f o r human occupation o f the New World during t h e P l e i s t o c e n e . The i s s u e s g e n e r a l l y r e s o l v e themselves down t o ( i ) can the a l l e g e d c u l t u r a l m a t e r i a l s be c o n c l u s i v e l y demonstrated t o be the product o f human agency and, ( i i ) what age assignment can be given t o these items? Much 1 4

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F i g u r e s i n brackets i n d i c a t e the l i t e r a t u r e references a t the end of t h i s paper.

0097-6156/82/0176-0453$05.25/0 © 1982 American Chemical Society Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

454

N U C L E A R A N D C H E M I C A L DATING T E C H N I Q U E S

of the debate has been focused on the f i r s t question s i n c e , t h e proposed " c u l t u r a l m a t e r i a l s " have been, almost without e x c e p t i o n , chipped stone [ 4 ] . The d a t i n g o f human s k e l e t a l m a t e r i a l s , would o b v i o u s l y render moot the question o f human agency as w e l l as t h e problem of a s s o c i a t i o n . Table 1. Assumptions o f the Radiocarbon Method P h y s i c a l Assumptions 1.

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The production o f C by cosmic rays has remained constant long enough t o have e s t a b l i s h e d a s t e a d y - s t a t e o r e q u i l i brium i n the C / C r a t i o i n the atmosphere; There has been a complete mixing o f C throughout t h e v a r i o u s carbon r e s e r v o i r s on a r e l a t i v e l y r a p i d time s c a l e ; The carbon isotope r a t i o s i n samples have not been a l t e r e d except by the decay o f C ; The t o t a l amount o f carbon i n the exchange system have remained constant; The decay constant ( o r h a l f - l i f e ) o f C i s known a t an a p p r o p r i a t e l e v e l o f p r e c i s i o n and accuracy; Natural l e v e l s o f C can be measured t o a p p r o p r i a t e l e v e l s of p r e c i s i o n and accuracy. 1 4


2. 3.

1 2

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4. 5. 6.

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Contextual 1.

Assumption

There i s a d i r e c t and s p e c i f i c a s s o c i a t i o n between a sample to be analyzed and event o r phenomena t o be dated.

Another area o f c u r r e n t a r c h a e o l o g i c a l and p a l e o a n t h r o p o l o g i c a l debate, where d i r e c t d a t i n g o f s k e l e t a l m a t e r i a l s i s o f c r u c i a l s i g n i f i c a n c e , i n v o l v e s t h e question o f the o r i g i n o f a n a t o m i c a l l y modern Homo sapiens. As a r e s u l t o f s t u d i e s con ducted over the l a s t decade, previous views o f the phylogenetic r e l a t i o n s h i p o f modern Homo sapiens t o presumed a n c e s t r a l forms, p a r t i c u l a r l y t h e Neanderthal v a r i e n t s o f Homo sapiens, have been undergoing major r e v i s i o n [ 5 ] . C r u c i a l t o these d i s c u s s i o n s a r e questions o f the accuracy o f the c h r o n o l o g i c a l framework f o r the r e l e v a n t f o s s i l and a r c h a e o l o g i c a l record. U n f o r t u n a t e l y , the time p e r i o d r e l e v a n t t o t h i s i s s u e i s c u r r e n t l y beyond t h e prac t i c a l o p e r a t i o n a l l i m i t f o r standard decay counting C systems. However, the development o f d i r e c t C counting methods, using high energy mass spectrometric a n a l y s i s , i s on the t h r e s h o l d o f p o t e n t i a l l y p r o v i d i n g the technology t o permit the d a t i n g o f organic m a t e r i a l s f o r the l a s t 1 0 years [6-8]. Many o f the s i t e s from which important f o s s i l and a r c h a e o l o g i c a l evidence are d e r i v e d c o n t a i n s i g n i f i c a n t q u a n t i t i e s o f faunal m a t e r i a l s , i n c l u d i n g , o f course, the hominid remains themselves. I f the accuracy o f C determinations on r e l a t i v e l y small q u a n t i t i e s o f P l e i s t o c e n e age bone c o u l d be demonstrated, then t h i s would permit d i r e c t age determinations on the c r i t i c a l f o s s i l samples. 1 4

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Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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TAYLOR

Problems in the Radiocarbon Dating of Bone

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U n t i l the development o f the C method, except f o r t h e use of f l u o r i n e and n i t r o g e n values as r e l a t i v e temporal i n d i c a t o r s , estimates o f the age o f human bone samples were based l a r g e l y on i n d i r e c t means. In New World s t u d i e s , f o r example, general geolog i c a l o r p a l e o n t o l o g i c a l c o n s i d e r a t i o n s were employed, i n c l u d i n g the degree o f morphological a f f i n i t y o f a given sample t o modern Native American p o p u l a t i o n s . I t was i n i t i a l l y assumed t h a t any pre-Holocene age Homo sapiens i n the New World would e x h i b i t morphological c h a r a c t e r i s t i c s s i m i l a r t o those observed on s k e l e t a l samples o f Homo o f s i m i l a r age i n Europe [ 9 ] . With the i n t r o d u c t i o n o f the C method, one might have expected t h a t the d i r e c t d a t i n g o f bone samples would have provided a standard means of e s t a b l i s h i n g age estimates. U n f o r t u n a t e l y , t h i s has not always proven t o have been the case. The paper w i l l review the problems of o b t a i n i n g r e l i a b l e C determinations on bone p a r t i c u l a r l y on bone samples o f presumed P l e i s t o c e n e age. R e l i a b l e age determina t i o n s on such samples would shed enormous l i g h t on the development of modern Homo sapiens i n the Eastern Hemisphere and t h e i r subse quent m i g r a t i o n to the New World.


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I n i t i a l Radiocarbon Determinations on Bone 1 4

From t h e beginning o f C s t u d i e s , bone was burdened w i t h a marginal s t a t u s as a sample type. I t was m i s s i n g from the l i s t o f sample m a t e r i a l s which Libby i n i t i a l l y recommended [10]. He and other researchers discouraged i t s use f o r the reason t h a t the carbon content and s p e c i f i c a l l y the organic carbon content, was low even i n r e l a t i v e l y recent bone and because i t was a very porous s t r u c t u r e p o t e n t i a l l y s u b j e c t t o chemical a l t e r a t i o n and presumably t o contamination. I t was concluded t h a t bone would s y s t e m a t i c a l l y v i o l a t e the t h i r d assumption o f the C method as l i s t e d i n Table 1. ( I t should be noted t h a t "burned bone" was h i g h l y recommended. However, the sample m a t e r i a l was the carbo n i z e d h a i r , s k i n , and other t i s s u e r a t h e r than the bone matrix itself.) In 1963, Edwin Olsson surveyed the e a r l y C l i t e r a t u r e as i t r e l a t e d t o problems o f sample contamination [11]. The negative r e p u t a t i o n o f bone was, by then, f i r m l y e s t a b l i s h e d as i s e v i denced i n h i s g r a p h i c a l summary o f opinions concerning the r e l a t i v e r e l i a b i l i t y o f d i f f e r e n t sample types ( f i g u r e 1). The consensus view was t h a t C dates based on bone were g e n e r a l l y u n r e l i a b l e . At the same time, the d i f f e r e n t i a l r e l i a b i l i t y o f the i n o r g a n i c as opposed t o t h e organic f r a c t i o n o f bone were recog nized. On one hand, "Bone carbonate i s w o r t h l e s s , " [ 1 2 ] , w h i l e Sinex and Fan's [13] argued t h a t the C d a t i n g o f " p u r i f i e d [bone] g e l a t i n would be as r e l i a b l e as charcoal d a t i n g o r p o s s i b l y more s o , s i n c e a n a l y t i c a l evidence may be obtained t h a t t h e organic m a t e r i a l i s what i t appears t o be, namely, "bone p r o t e i n " . Berger e t a l . [ 1 4 ] p u b l i s h e d t h e f i r s t extended s e r i e s o f C determinations on the c o l l a g e n f r a c t i o n o f bone (Table 2). I t 1 4

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456


KEY ACCEPTABLE


ACCEPTABLE (WITH RESERVATION) REJECTED (WITH RESERVATION) REJECTED

WOOD

CHARCOAL-

BONE

Figure 1.

Relative acceptability of six types of sample materials in early radiocarbon literature (adapted from Réf. 11).


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457

was c l e a r t h a t a s p e c i f i c organic component o f Holocene age bone could be prepared which y i e l d e d C values i n concordance w i t h standard sample types. The d i s c o r d a n t values were a t t r i b u t e d t o the l a c k o f good a s s o c i a t i o n o f bone w i t h the c o n t r o l samples o r , as was the case w i t h the Chicago sample (C-302), the anomalous age was a t t r i b u t e d t o problems w i t h the reagents used i n the e a r l y phase o f s o l i d carbon p r e p a r a t i o n s . 1 4

Table 2.


Sample No.

Concordance o f S u i t e o f Radiocarbon Determinations on Bone Collagen and A s s o c i a t e d Organics. Source: Berger e t aJL [14] and Personal Communication. Provenience

Radiocarbon Age ( C y r s . B.P.)

Sample Type

1 4

UCLA-684

bone c o l l a g e n

1800Π00

charcoal

2270±110


2500180

skin

2510±80


3970Π00

charcoal

4260±85


8750±120

UCLA-697B

charred t i s s u e (burned bone)

88401140

C-302

charred t i s s u e (burned bone)

68761250 (average)

Hastinapur, India

TF-90 UCLA-689

Chimney Cave, Nevada

UCLA-690 UCLA-692

Santa Rosa I s l a n d , Ca.

UCLA-140(B) UCLA-697A

Sage Creek, Wyoming

1 4

Since t h a t time, a s i z a b l e number o f bone c o l l a g e n C determinations have been published. Several have f i g u r e d pre dominantly i n d i s c u s s i o n s concerning the a n t i q u i t y o f Homo sapiens i n the New World. For example, C determinations on two s k e l e t a l samples from southern C a l i f o r n i a have y i e l d e d s u r p r i s i n g l y e a r l y dates. C determinations on the organic f r a c t i o n o f s k e l e t a l m a t e r i a l s excavated i n 1933 from Laguna Beach, a c o a s t a l suburb south o f Los Angeles, y i e l d e d values o f >14,800 (UCLA-1233B) and 17,150 1 1470 (UCLA-1233A) C years [15,16]. Likewise, * C values were obtained on s k e l e t a l m a t e r i a l s excavated i n 1936 by WPA crews i n t h e Baldwin Hills section of west-central Los Angeles. The C values on "Los Angeles Man" was >23,600 (UCLA1430) C years [16,17]. On the other hand, C determinations on the c o l l a g e n f r a c t i o n o f two s k e l e t a l samples from South America have r e s u l t e d i n a s i g n i f i c a n t r e d u c t i o n i n t h e i r p r e v i o u s l y 1 4

1 4

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458

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C H E M I C A L DATING T E C H N I Q U E S

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assumed age. On the b a s i s of C and thermoluminescence determina t i o n s on carbonates, an age of approximately 30,000 years had been assigned to a skeleton excavated from Otavalo, Ecuador [18,19]. On the b a s i s of C determinations on the c o l l a g e n f r a c t i o n of two bones, the age of the skeleton was determined t o be no more than about 3,000 C years [20,21]. Likewise, a collagen-based C determination on a human cranium from Puni η, Ecuador, thought t o be P l e i s t o c e n e i n age y i e l d e d on age of 6,900 ± 250 C years [22]. Although i n c r e a s i n g confidence has been placed i n the v a l i d i t y of C determinations on bone organic f r a c t i o n s , t h i s acceptance had tended to be l e s s e n t h u s i a t i c when P l e i s t o c e n e age bone samples are involved. When r e l a t i v e l y l a r g e amounts of c o l l a g e n i s a v a i l a b l e f o r p r o c e s s i n g , more confidence has been placed i n the r e s u l t i n g age. However, when the organic carbon content of the bone s l i p s below approximately the 0.5 percent l e v e l , concern has been expressed as whether the recoverable organic f r a c t i o n i s a c t u a l l y indigenous t o the bone or might be contaminated by m i g r a t i n g s o i l organics. For example, response to the p u b l i c a t i o n of the C a l i f o r n i a p a l e o i n d i a n C values i n d i c a t e d a s i g n i f i c a n t degree of r e t i c e n c e i n accepting these r e s u l t s . As one s e n i o r American a r c h a e o l o g i s t has commented, "the c o l l a g e n d a t i n g of human skeletons [ i n C a l i f o r n i a ] i s suggestive but no more - of very e a r l y h a b i t a t i o n i n the area" [23]. 14

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Preparation of Bone Samples f o r C

Analysis

Table 3 l i s t s the d i f f e r e n t i n o r g a n i c and organic f r a c t i o n s which have been u t i l i z e d to o b t a i n C determinations on bone. While there are v a r i a t i o n s between d i f f e r e n t species as w e l l as between d i f f e r e n t bones and bone s t r u c t u r e s w i t h i n the same animal, g e n e r a l l y speaking, the i n o r g a n i c f r a c t i o n c o n s t i t u t e s about 70 to 80 percent of f r e s h , dry compact bone [24]. In the m a j o r i t y of samples d e r i v e d from most a r c h a e o l o g i c a l or g e o l o g i c a l c o n t e x t s , t h i s f r a c t i o n i s composed of ( i ) the o r i g i n a l a p a t i t e component of the bone and ( i i ) d i a g e n e t i c or secondary carbonate. The C a c t i v i t y of the secondary carbonate f r a c t i o n g e n e r a l l y r e f l e c t s the degree of i s o t o p i c exchange w i t h groundwater. Thus i t i s t r u l y "worthless" i n terms of d a t i n g the bone. By c o n t r a s t , several researchers have argued t h a t the a p a t i t e f r a c t i o n should not have been subject t o exchange. Experiments using the a p a t i t e component in bone have u n f o r t u n a t e l y yielded inconsistent r e s u l t s . Under c e r t a i n c o n d i t i o n s , C a n a l y s i s on t h i s f r a c t i o n seem t o y i e l d accurate values [25]. However, geochemical and m i n e r a l o g i c a l s t u d i e s have revealed a number of mechanisms which can s i g n i f i c a n t l y a l t e r the carbon isotope values i n a p a t i t e s t r u c t u r e s [26,27]. Such o b s t a c l e s may not completely exclude i t s use f o r d a t i n g bone, as some other workers, more r e c e n t l y , have been r e p o r t i n g more encouraging r e s u l t s [28]. 14

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Table 3.

Components o f Bone Used f o r Radiocarbon

459 Determinations

Inorganic F r a c t i o n s Diagenetic o r Secondary Carbonate Apatite Organic F r a c t i o n s A c i d s o l u b l e , i n s o l u b l e , undissolved f r a c t i o n s ( t o t a l and s p e c i f i c molecular weight ranges)


Collagen Gelatin Total Amino Acids 1 4

The questionable r e l i a b i l i t y o f most C determinations on most o f the i n o r g a n i c components o f bone has l e d t h i s , as w e l l as many other researchers, t o concentrate on one o r more o f the organic f r a c t i o n s [29-31]. In modern dry, f a t - f r e e bone, over 90 percent o f the organics e x i s t i n the form o f the p r o t e i n c o l l a gen w i t h the remaining non-collagenous p r o t e i n s composed o f a complex assortment o f , as y e t , incompletely c h a r a c t e r i z e d organic substances [32]. In l i v i n g bone, c o l l a g e n i s deposited i n a dense framework o f laminated f i b e r s w i t h a h i g h l y s p e c i f i c p h y s i c a l s t r u c t u r e [33]. In the case o f most bone d e r i v e d from the t y p i c a l g e o l o g i c a l o r a r c h a e o l o g i c a l s i t e , however, i t appears t h a t one i s not d e a l i n g w i t h unaltered c o l l a g e n [34]. Thus, i t i s probably more appropriate t o use the term, " c o l l a g e n - d e r i v e d " when r e f e r r i n g t o t h i s organic component i n bone as i t has been a f f e c t e d by diagenetic conditions. Emphasis should a l s o be placed on t h e danger o f using the terms, " c o l l a g e n " o r " c o l l a g e n - d e r i v e d " simply as synonyms f o r the a c i d s o l u b l e , i n s o l u b l e o r undissolved f r a c tions. I t should not be a u t o m a t i c a l l y assumed t h a t any o f these p r e p a r a t i o n s , e s p e c i a l l y i n P l e i s t o c e n e age bone, w i l l n e c e s s a r i l y c o n t a i n o n l y , o r even p r i m a r i l y , c o l l a g e n - d e r i v e d organics without independent c o n f i r m a t i o n . Several procedures have been employed t o prepare v a r i o u s organic f r a c t i o n s o f bone f o r C analyses. The most extensive p u b l i s h e d a n a l y s i s o f the r e l a t i v e merits o f the d i f f e r e n t chemi c a l pretreatment approaches i s a v a i l a b l e as a r e s u l t o f the long term s t u d i e s o f I n g r i d Olsson and her c o l l a b o r a t o r s [35-40] and of A f i f a Hassan [41-43]. A l l chemical pretreatments assume an i n i t i a l p h y s i c a l examination o f the e x t e r n a l surface and f r a c t u r e zones t o i n s u r e t h e removal o f p r e s e r v a t i v e s , microorganisms, and humic m a t e r i a l s , r o o t l e t s and other non-bone organic fragments [42]. Chemical processing i n v o l v e s i n i t i a l l y t h e e l i m i n a t i o n o f the i n o r g a n i c carbonates. Both EDTA and HC1 have been used f o r t h i s purpose [14,36]. However, f e a r o f contamination w i t h " o l d " 1 4


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N U C L E A R AND



14

carbon ( c o n t a i n i n g no C) from the EDTA treatment has been expressed [36,41]. Such a problem can apparently be minimized or e l i m i n a t e d w i t h s u f f i c i e n t washing [38]. Further p r e p a r a t i o n s have i n c l u d e d conversion t o g e l a t i n [13,44-46], treatment w i t h NaOH t o remove humâtes and other base s o l u b l e f r a c t i o n s [36,46, 4 7 ] , and the s e p a r a t i o n of t o t a l amino a c i d s or a s i n g l e amino a c i d [30,48]. In every case, the goal of any pretreatment procedure i s to i s o l a t e one or more "uncontaminated" organic f r a c t i o n ( s ) which i s (are) unambiguously indigenous t o the o r i g i n a l bone sample. The s t r a t e g i e s employed to accomplish t h i s , however, must conform t o the r e a l i t y of the degree of p r e s e r v a t i o n of the organics i n a p a r t i c u l a r sample. Where the organic carbon content i s r e l a t i v e l y high (e.g., >1 gram organic carbon depending on the counting system employed), one can use r e l a t i v e l y r i g o r o u s sample p r e t r e a t ment techniques. Where the organic carbon content i s s i g n i f i c a n t l y l e s s than t h i s , care must be e x e r c i s e d so t h a t the sample s i z e f o l l o w i n g the completion of the pretreatment does not drop below acceptable l i m i t s i n terms of counting requirements. Thus, an important requirement of any chemical or p h y s i c a l p r o c e s s i n g technique i s t h a t i t can be f l e x i b l y a p p l i e d t o maximize the removal of non-indigenous organics w h i l e minimizing l o s s of autochthonous organics. Various c r i t e r i a have been employed i n an attempt to i d e n t i f y those bone samples, of low organic carbon y i e l d , where d i a g e n e t i c e f f e c t s may have contaminated the indigenous organic f r a c t i o n ( s ) . One q u a n t i t a t i v e approach might be c a l l e d the "pseudomorph" t e s t . Figure 2a i l l u s t r a t e s where d e m o r a l i z a t i o n of a bone from a l a t e Roman/Christian cemetary i n England l e f t behind an organic r e p l i c a or pseudomorph of the o r i g i n a l bone s t r u c t u r e . By c o n t r a s t , the same treatment of a bone sample from a P l e i s t o c e n e s i t e i n North A f r i c a y i e l d s a product, i n which the o r i g i n a l p h y s i c a l s t r u c t u r e of the bone i s t o t a l l y l o s t ( f i g u r e 2b). U n f o r t u n a t e l y , a high degree of p h y s i c a l degradation i n the bone matrix may or may not c o r r e l a t e w i t h the presence of s i g n i f i c a n t amounts of non-in s i t u organics. Most bones, from the m a j o r i t y of environments w i t h ages of s e v e r a l thousands or tens of thousands of y e a r s , would substan t i a l l y " f l u n k " the pseudomorph t e s t . Many of these samples, however, would y i e l d apparently acceptable C values. More q u a n t i t a t i v e methods need t o be evaluated which can be employed to i d e n t i f y bones w i t h p o t e n t i a l l y s e r i o u s contamination problems. 14

E v a l u a t i n g Contamination E f f e c t s In reviewing v a r i o u s s t r a t e g i e s t h a t might be used t o e v a l uate the d i f f e r e n t i a l e f f e c t s of contamination, i t might be h e l p f u l t o b r i e f l y c o n s i d e r the r e l a t i o n s h i p between the " a c t u a l C age" and "apparent C age" of samples to which have been added v a r y i n g amounts of non-indigenous organic m a t e r i a l . Two simple models can be employed t o evaluate such c o n d i t i o n s . The 14

14



461


23. TAYLOR

Figure 2. Organic residue following demoralization of human bone sample from (a) late Roman/Christian cemetery near Poundbury, Dorchester, England (sample supplied by Theya Molleson, British Museum) and (b) Upper Paleolithic site in North Africa. Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

462

N U C L E A R AND


f i r s t i n v o l v e s p l o t t i n g the e f f e c t s of the a d d i t i o n of modern carbon t o samples of v a r y i n g " t r u e or a c t u a l age". Figure 3 represents a summary of the r e l a t i o n s h i p between a c t u a l and apparent ages i n samples to which have been added v a r y i n g percent ages of contemporary carbon. Except a t the l e v e l of f i v e percent modern carbon, t h i s p l o t shows t h a t up to around 20,000 y e a r s , the e f f e c t on the d i l u t i o n age i s on the order of the t y p i c a l s t a t i s t i c a l e r r o r f o r decay counting systems. Contamination w i t h modern carbon on the order of 0.5 to 1 percent does, however, l i m i t the confidence one can have w i t h bone t o about 35,000 C years. For those who are concerned w i t h the p r e p a r a t i o n of samples f o r the d i r e c t C counting systems, t h i s summary v i v i d l y i l l u s t r a t e s the e f f e c t s on the f i n a l age value as a r e s u l t of the a d d i t i o n of ppm l e v e l s of modern carbon f o r samples i n d i f f e r e n t age ranges. For a sample w i t h an a c t u a l age of 75,000 y e a r s , f o r example, a 100 ppm a d d i t i o n of modern carbon r e s u l t s i n a p p r o x i mately a 5000-year e r r o r i n the f i n a l measured age. H o p e f u l l y , contamination of a sample w i t h modern carbon would be a r e l a t i v e l y r a r e occurrence. A more probable s i t u a t i o n would i n v o l v e the a d d i t i o n of carbon d i f f e r i n g i n age from the o r i g i n a l samples from several hundred up t o s e v e r a l tens of thousands of years. Olsson [37] p r e v i o u s l y provided a p l o t of the e f f e c t s of i n t r o d u c i n g v a r y i n g amounts of organic m a t e r i a l s w i t h age d i f f e r ences of up t o 5,000 years between sample and contaminant. Figure 4 has extended her c a l c u l a t i o n s to show the e f f e c t of the i n t r o d u c t i o n of 0.5 percent to 30 percent contaminants w i t h age d i f f e r e n c e s of up t o 50,000 years. These data show t h a t f o r Holocene samples contaminated w i t h up to f i v e percent of m a t e r i a l w i t h a d i f f e r e n t i a l age of not more than 5,000 y e a r s , the e f f e c t s g e n e r a l l y are w i t h i n the range of the t y p i c a l one sigma counting e r r o r s f o r decay counting systems. Up to a 1.0 percent d i l u t i o n w i t h organics not more than about 20,000 years younger than the indigenous samples, the age r e d u c t i o n does not exceed about 1000 years. Figure 4 a l s o shows the e f f e c t s from 10 percent to 30 percent sample contamination w i t h younger m a t e r i a l s . Samples w i t h t h i s degree of contamination would almost c e r t a i n l y be i d e n t i f i e d d u r i n g sample p r e p a r a t i o n steps and a p p r o p r i a t e pretreatment s t r a t e g i e s employed. Even w i t h a 10 percent contamination f a c t o r , however, i f the d i f f e r e n t i a l age of the contamination w i t h respect to the autochthonous sample does not exceed about 10,000 y e a r s , the anomaly thus created i s on the order of about 2,000 years. In a n t i c i p a t i o n of the development to o p e r a t i o n a l s t a t u s of the i o n or d i r e c t counting systems, i t would be h e l p f u l i f we c o u l d compare these values w i t h p r o j e c t e d counting e r r o r s f o r the two types of d i r e c t counting systems being developed. Table 4 l i s t s p r o j e c t i o n s f o r the Rochester Van de G r a a f f f a c i l i t y [49] and the U n i v e r s i t y of C a l i f o r n i a Lawrence Berkeley c y c l o t r o n system employing an e x t e r n a l i o n source [31,50]. Table 4 a l s o l i s t s the sample s i z e s and approximate measurement periods f o r both systems. This data i l l u s t r a t e s the p o t e n t i a l extent!on i n d a t i n g 14


14


TAYLOR



23.


463


15 mi η 100 min

±100

50 mg

(C)** 10,000

100 min

±240

50 mg

(C)** 25,000

100 min

±1100

50 mg

(C)** 50,000

2 hrs

±500

2-5 mg

(VG)* 60,000

100 min

±5000

50 mg

(C)** 75,000

Van de G r a a f f System ( R o c h e s t e r ) : Source: r e f e r e n c e 49. * C y c l o t r o n System ( B e r k e l e y ) : Source; T. S. Mast, personal communication.

Time Needed/ Measurement

±25

1 mg

Sample S i z e

Approximate Counting E r r o r (1 sigma)

(VG)* Modern

120 mg

(VG)* 100,000

1 day

±2500

Expected Counting Parameters f o r D i r e c t Counting o f Radiocarbon

Sample Age

Table 4.



23.

TAYLOR


465

range and major r e d u c t i o n i n sample s i z e s t h a t t h e o r e t i c a l l y should be p o s s i b l e w i t h high energy spectrometric methods. Obviously, both o f these c h a r a c t e r i s t i c s would o f f e r s i g n i f i c a n t advantages i n d a t i n g bone samples w i t h low organic carbon y i e l d s and documenting the time p e r i o d on which our s t u d i e s are p a r t i c u l a r l y focussed. I t should be noted t h a t the counting e r r o r values are c a l c u l a t e d on the b a s i s o f s t a t i s t i c s alone and do not take i n t o account any e r r o r introduced because o f instrumental v a r i a b i l i t y . A l s o , there i s s i g n i f i c a n t d i f f e r e n c e i n e r r o r estimates between the Van de G r a a f f and c y c l o t r o n f a c i l i t y because o f d i f f e r e n t assumptions concerning counting e f f i c i e n c i e s and back ground l e v e l s . The background l e v e l s i n the instruments a r e t h e p r i n c i p a l l i m i t i n g f a c t o r i n r e a l i z i n g the t h e o r e t i c a l e x t e n t i o n i n the d a t i n g range i n t o the 1 0 year region [ 7 ] . Of equal importance w i l l be the a b i l i t y t o exclude contaminating o r g a n i c s , as we have i l l u s t r a t e d w i t h the data i n f i g u r e s 3 and 4 [51]. 6

I d e n t i f i c a t i o n o f Non-Autochthonous Organics i n Bone Samples Several methods a r e c u r r e n t l y being evaluated t o determine whether one o r more o f them can be employed t o i d e n t i f y bone samples which c o n t a i n unacceptable amounts on non-indigenous organics. One approach i s examining s t a b l e isotope data as a means o f monitoring the t r a n s p o r t o f organics from the surrounding environment i n t o t h e bone matrix. Although both hydrogen (D/H) and carbon ( C / C ) isotope data on bone have been examined [ 3 1 ] , recent a t t e n t i o n has been focussed on n i t r o g e n ( N / N ) values. P o t e n t i a l f r a c t i o n a t i o n e f f e c t s r e s u l t i n g from the a c i d h y d r o l y s i s procedures used t o i s o l a t e the t o t a l organic f r a c t i o n have been i n v e s t i g a t e d (Table 5 ) . Modern mammalian bone samples from n a t u r a l and c a p t i v e ( z o o ) environments have been examined tô determine the e f f e c t o f s p e c i e s , environmental, and d i e t a r y v a r i a b i l i t y , w h i l e measurements on Holocene and l a t e P l e i s t o c e n e a r c h a e o l o g i c a l and p a l e o n t o l o g i c a l samples have been obtained t o identify potential diagenetic processes affecting isotopic composition ( f i g u r e 5). The b a s i s o f t h i s study i s the suggestion t h a t organic f r a c t i o n s not indigenous t o a bone w i l l manifest d i s t i n c t i v e s t a b l e isotope p a t t e r n s . I t has been e x p e r i m e n t a l l y determined t h a t N values i n bone c o l l a g e n i s d i r e c t l y r e l a t e d t o t h e N value o f the d i e t w i t h t h e c o l l a g e n being enriched by some 2-3 per m i l w i t h respect t o the d i e t a r y source [54]. I f i t can be shown t h a t t h e isotope values a t t r i b u t a b l e t o i n i t i a l environmental ( i n c l u d i n g d i e t a r y ) and d i a g e n e t i c processes can be d i s t i n g u i s h e d from t h a t caused by as a r e s u l t o f t h e t r a n s p o r t i n t o t h e bone matrix o f organic m a t e r i a l e x t e r n a l t o the bone i t s e l f , then such values can be used as c r i t e r i a t o i n d i c a t e t h e presence o f contaminants. Table 5 c o n t r a s t s the N values obtained from whole bone samples (no pretreatment) as opposed t o samples subjected t o very r i g o r o u s and extended a c i d h y d r o l y s i s [55]. Measurements conducted on 1 3

1 2

15

14

1 5

1 5

1 5


466



30|

DIFFERENCE BETWEEN ACTUAL SAMPLE AGE AND AGE OF YOUNGER CONTAMINANT (YRS. X 1000)

Figure 4. Reduction in age of samples resulting from addition of 0.5 to 30 organics with 10,000 to 50,000 year younger age (after Ref. 31).

AIR

U

LAND PLANTS SOILS

0

b

MARINE PLANTS

0

MARINE ANIMALS

0

MODERN BONE ORGANICS 0

HOLOCENE/LATE PLEISTOCENE BONE 0R6ANICS -10 C

+5

+10

•15

•20

•25

S N ( P E R MIL) ,5

Figure 5. Nitrogen isotope measurements on various components of the na environment. The N values expressed with respect to AIR. (Λ) Data from R 52; (b) data from Ref. 53; and (c) data from Ref. 31. 15



Sample

2

3

None (whole bone)

Total Hydrolyses (organic f r a c t i o n )

P e r m i l expressed w i t h r e f e r e n c e t o AIR.

d

+8.38

1 4

See r e f e r e n c e 31.

+6.67 -

+7.30

+10.98

+10.20 - +11.76

+6.00

+5.67

+6.21

Average

+6.16

+4.34 -

+5.56 -

1

B o t h o r g a n i c and a p a t i t e f r a c t i o n s y i e l d e d age o f approximately 18,000 C years.

C o m p l e t e d i s s o l u t i o n o f bone m a t r i x i n 12N HC1 f o r 12 hrs.

G. Rau, personal communication.

b

0

a

P l e i s t o c e n e Bone (Mammuthus columbi)

3

Total Hydrolyses (organic f r a c t i o n )

0

7

None (whole bone)

N Values Range

1 5

N Values o f Contemporary and Late

Replication

c

1 5

Pretreatment

P l e i s t o c e n e Bone Samples

E f f e c t o f V a r i a t i o n i n Pretreatment Methods on

Modern Bone (Bos t a u r u r u s )

Table 5.


468

N U C L E A R A N D C H E M I C A L DATING

TECHNIQUES

r e p l i c a t e samples, using techniques t o be d e s c r i b e d elsewhere [ 5 6 ] , i n d i c a t e an a c t u a l p r e c i s i o n f o r bone N measurements o f about ± 1.5 per m i l . Measurements on modern bone show no s i g n i f i c a n t e f f e c t s as a r e s u l t o f the hydrolyses technique employed. These measurements confirm the e x p e c t a t i o n t h a t e s s e n t i a l l y a l l o f the n i t r o g e n contained i n contemporary bone i s d e r i v e d from the organic f r a c t i o n which i s predominantly c o l l a g e n . Comparison o f the N values of the whole bone and organic f r a c t i o n o f a l a t e P l e i s t o c e n e bone (Mammuthus columbi) dated a t about 18,000 C years B.P. r e v e a l s d i f f e r e n c e s on the order o f 3 per mil. Whether t h i s d i f f e r e n c e can be a t t r i b u t e d t o d i a g e n e t i c e f f e c t s (presence of non-organic n i t r o g e n ) o r other f a c t o r s i s c u r r e n t l y under study. Figure 5 compares the range i n N values f o r f o u r n i t r o g e n c o n t a i n i n g segments o f the n a t u r a l environment compared w i t h N measurements on the t o t a l organic f r a c t i o n o f modern and archaeo l o g i c a l / p a l e o t o l o g i c a l bone samples [ 3 1 ] . Measurements obtained to-date on modern bone suggest t h a t the maximum v a r i a b i l i t y i n N values a t t r i b u t a b l e t o s p e c i e s , environmental, o r d i e t a r y causes i s on the order o f 10 per m i l . Based on N values obtained from land p l a n t s and s o i l samples, we would expect the range t o be much g r e a t e r than t h i s e s p e c i a l l y i f the d i e t o f an animal r e f l e c t e d the e x p l o i t a t i o n o f marine resources. A d d i t i o n a l measurements on modern bone w i l l be necessary t o c o n c l u s i v e l y document non-diagenetic v a r i a b i l i t y . The use o f amino a c i d composition and/or racemization values as a means o f c h a r a c t e r i z i n g the organic c o n s t i t u e n t s o f f o s s i l bone has been p r e v i o u s l y suggested by s e v e r a l researchers [31,32, 43]. Collagen i n modern bone i s c h a r a c t e r i z e d by a high g l y c i n e content, r e l a t i v e l y high p r o l i n e , and the presence o f hydroxyprol i n e and hydroxylyxine. Except f o r a l i m i t e d d i s t r i b u t i o n i n some p l a n t e x t r a c t s , hydroxyproline has been found o n l y i n the h y d r o l yses products o f c o l l a g e n and i t s d i a g e n e t i c d e r i v a t i v e s . A c h a r a c t e r i s t i c o f most amino a c i d s i s t h a t they can e x i s t i n one or two p o s s i b l e o p t i c a l forms designed as D- and L-. The amino a c i d s i n most l i v i n g organisms c o n s i s t only o f L-amino a c i d s . At the death, f o r example, o f an animal, the amino a c i d s contained i n the p r o t e i n s o f the bone s t r u c t u r e w i l l begin t o be s u b j e c t t o chemical changes which r e s u l t s i n p r o g r e s s i v e a l t e r a t i o n s i n the r e l a t i v e p o r t i o n s o f the v a r i o u s amino a c i d s as w e l l , i n the case of most amino a c i d s , i n the L-forms changing i n t o t h e i r c o r r e sponding D-form. As i s well-known, racemization ( o r e p i m e r i z a t i o n as i n the case o f i s o l e u c i n e ) has been used as an independent means of d a t i n g f o s s i l bone [57,58] w i t h some however, expressing s e r i o u s r e s e r v a t i o n as t o the v a l i d i t y o f many o f the amino a c i d racemiza t i o n dates [59,61]. The use o f the r e l a t i v e p r o p o r t i o n s and racemization proper t i e s o f amino a c i d s as a means o f i d e n t i f y i n g contaminated samples would have s e v e r a l advantages. F i r s t o f a l l , modern amino a c i d a n a l y z e r s are very s e n s i t i v e a n a l y t i c a l instruments. Systems are 1 5

1 5


1 4

1 5

1 5

1 5

1 5


23. TAYLOR Problems in the Radiocarbon Dating of Bone

469

now a v a i l a b l e which can obtain q u a n t i t a t i v e amino a c i d composition analyses with simultaneous determination of D/L r a t i o s on a wide assortment of amino acids employing extremely small amounts of sample [62]. This would permit measurements to be made on samples even when the preservation c o n d i t i o n s are extremely poor. An a d d i t i o n a l advantage would be the a b i l i t y to increase the number of bone samples f o r which there would be both d i r e c t C and amino a c i d racemization determinations. Perhaps, t h i s data set would c o n t r i b u t e to r e s o l v i n g some of the issues surrounding the question of the v a l i d i t y of amino a c i d racemization deduced age values. Several studies are c u r r e n t l y underway to examine the use of amino a c i d data as a means of i d e n t i f y i n g biochemically anomalous bone samples. Probably the most d i r e c t approach to the problem of contamina t i o n i n bone would be to obtain m u l t i p l e C determinations on d i f f e r e n t organic f r a c t i o n s of the same sample ( c f . Table 3). The r e l i a b i l i t y of the C determinations would be a f u n c t i o n of the degree of concordance of the ages r e f l e c t e d i n the d i f f e r e n t organic f r a c t i o n s . In cases where the degree of organic preserva t i o n permits, t h i s approach can be and has been employed w i t h success [38,39]. U n t i l the advent of high energy mass spectro m e t r y methods of measurement, however, i t g e n e r a l l y was not p r a c t i c a b l e t o pursue t h i s approach w i t h most bone samples recovered from Pleistocene s i t e s except where r e l a t i v e l y large amounts of bone was a v a i l a b l e . When operational status f o r the d i r e c t C dating systems are achieved, the e x t r a c t i o n and dating of s i n g l e amino acids such as hydroxyproline, known to have l i m i t e d d i s t r i b u t i o n except as a c o n s t i t u e n t amino a c i d of c o l l a g e n , would provide the most secure approach i n the dating of P l e i s t o c e n e bone. Probably more common, however, w i l l be the dating of a c i d s o l u b l e and i n s o l u b l e f r a c t i o n s before and a f t e r base e x t r a c t i o n s and f o l l o w i n g conversion to g e l a t i n e [63]. This approach might be augmented by d a t i n g various f r a c t i o n s of d i f f e r e n t molecular weights. The basis of t h i s i s the suggestion t h a t non-in s i t u organics i n bone w i l l g e n e r a l l y be of lower molecular weight than the r e s i d u a l autochthonous organics. The a b i l i t y to obtain C determinations on 10-100 m i l l i g r a m s i z e samples of geochemically c h a r a c t e r i z e d organic f r a c t i o n s of bone should a l l o w t h i s sample type to be r o u t i n e l y employed along with charcoal and other more standard sample types i n f u t u r e C studies [64].


14

14

14

14

14

14

References [1] Olsson, I. U., ed., Radiocarbon Variations and Absolute Chronology, Almqvist and Wiksell, Stockholm, 1970. [2] Rafter, Τ. Α., Grant-Taylor, T., eds., Proceedings of the 8th International Conference on Radiocarbon Dating, Royal Society, Wellington, 1973. [3] Berger, R., Suess, Η. Ε., eds., Radiocarbon Dating, University of California Press, Berkeley, 1979.



470 NUCLEAR AND CHEMICAL DATING TECHNIQUES

[4] Taylor, R. E., Payen, L. Α., The Role of Archaeometry in American Archaeology: Approaches to the Evaluation of the Antiquity of Homo sapiens in California, In: Advances in Archaeological Method and Theory, Vol. 2, pp. 239-283, Academic Press, New York, 1979. [5] Trinkhaus, E., Howells, W. W., The Neanderthals, Scientific American, 1979, 241, 94-105. [6] Muller, R. Α., Radioisotope Dating with a Cyclotron, Science 1977, 196, 489-494. [7] Stuiver, Μ., Carbon-14 Dating; A Comparison of Beta and Ion Counting, Science, 1978, 202, 881-883. [8] Berger, R., Radiocarbon Dating with Accelerators, Journal of Archaeological Science, 1979, 6, 101-104. [9] Hrdlicka, Α., Skeletal Remains Suggesting or Attributed to Early Man in North America, Smithsonian Institution, Bureau of American Ethnology. Bulletin 33. Washington, Government Printing Office, 1907. [10] Libby, W. F., Radiocarbon Dating, p. 44, Chicago, University of Chicago Press, 1955. [11] Olsson, Ε., The Problem of Sample Contamination in Radio carbon Dating, unpublished doctoral dissertation, Columbia University, 1963. [12] Olsson, Ε. Α., Broecker, W. S., Lamont Natural Radiocarbon Measurements VII, Radiocarbon, 1961, 3, 141-175. [13] Sinex, F. Β., Faris, Β., Isolation of Gelatin from Ancient Bones, Science, 129, 969. [14] Berger, R., Horney, A. G., Libby, W. F., Radiocarbon Dating of Bone and Shell from Their Organic Components, Science, 1964, 144, 999-1001. [15] Berger, R., Libby, W. F., UCLA Radiocarbon Dates IX, Radio carbon, 1969, 11, 194-209. [16] Berger, R., Protsch, R., Reynolds, R., Roxaire, C., Sackett, J. R., New Radiocarbon Dates Based on Bone Collagen in California Paleoindians, Contrib. Univ. Calif. Archaeol. Res. Fac., 1971, 12, 43. [17] Berger, R., Advances and Results in Radiocarbon Dating: Early Man in America, World Archaeology, 1975, 7, 174-184. [18] Davies, D. Μ., Fossil Man in Ecuador, Spectrum, 1973, 106, 4215. [19] Davies, D. Μ., Some Observations on the Otavalo Skeleton and Other Ramains of Early Man in South America, Journal of Human Evolution, 1978, 7, 279-281. [20] Brothwell, D., Burleigh, R., On Sinking Otavalo Man, Journal of Archaeological Science, 1977, 4, 291-294. [21] Burleigh, R., On the Dating of a Human Skeleton from Otavalo, Ecuador, Journal of Human Evolution, 1980, 9, 153. [22] Brothwell, D., Burleigh, R., The Human Cranium from Punin, Ecuador, with Particular Reference of Morphology and Dating, Journal of Archaeological Science, 1980, 7, 97-99.



23. TAYLOR Problems in the Radiocarbon Dating of Bone All

[23] Willey, G. Η., A Summary Scan, In: Chronologies in New World Archaeology, p. 528, New York, Academic Press, 1978. [24] Herring, G. Μ., The Organic Matrix in Bone, In: Biochemistry and Physiology of Bone, 2nd Edition, pp. 128-189, New York, Academic Press, 1972. [25] Haynes, C. V., Radiocarbon: Analysis of Inorganic Carbon of Fossil Bone and Enamel, Science, 1968, 161, 687-688. [26] Hassan, Α. Α., Geochemical and Mineralogical Studies on Bone Material and their Implications for Radiocarbon Dating, unpublished doctoral dissertation, Southern Methodist University, 1976. [27] Hassan, Α. Α., Termine, J. D., and Haynes, C. V., Mineralog ical Studies on Bone Apatite and their Implications for Radiocarbon Dating, Radiocarbon, 1977, 19, 364-374. [28] Hass, Η., Banewics, J. J., Radiocarbon Dating of Bone Apatite Using Thermal Release of CO , Radiocarbon, 1980, in press. [29] Taylor, R. Ε., Radiocarbon Dating: An Archaeological Perspec tive, In: Archaeological Chemistry II, pp. 33-69, Washington, D.C., American Chemical Society, 1978. [30] Taylor, R. Ε., Slota, P., Fraction Studies on Marine Shell and Bone Samples for Radiocarbon Analyses, In: Radiocarbon Dating, pp. 422-432, Berkeley University of California Press, 1979. [31] Taylor, R. Ε., Radiocarbon Dating of Pleistocene Bone: Toward Criteria for the Selection of Samples, Radiocarbon, 1980, in press. [32] Hare, P. Ε., Organic Geochemistry of Bone and Its Relation to the Survival of Bone in the Natural Environment, In: Fossils in the Making: Vertebrate Taphonomy and Paleoecology, Chicago, University of Chicago Press, 1979. [33] Miller, E. J., The Collagen of Bone and Cartilage, In: The Biochemistry and Physiology of Bone, 2nd Edition, pp. 1-20, New York, Academic Press, 1972. [34] Tuross, Ν., Hare, P. Ε., Collagen in Fossil Bone, Carnegie Inst, of Washington Yearbook, 1978, 77, 891-895. [35] Olsson, I. U., Modern Aspects of Radiocarbon Dating, EarthScience Reviews, 1968, 4, 203-218. [36] Olsson, I. U., El-Daoushy, M. F. A. F., Abd El-Mageed, A. I., Klasson, Μ., A Comparison of Different Methods for Pretreat ment of Bones. I, Geol. Fören Stockholm Förh, 1974, 96, 171181. [37] Olsson, I. U., Some Problems in Connection with the Evaluation of C Dates, Geol. Fören Stockholm Förh, 1974, 96, 311-320. [38] Fakid, A. F., El-Daoushy, M. F. A. F., Olsson, I. U., and Oro, F. Η., The EDTA and HCl Methods of Pre-treating Bones, Geol. Fören Stockholm Förh, 1978, 100, 213-219. [39] Olsson, I. U., El-Daoushy, M. F. A. F., Uppsala Natural Radiocarbon Measurements XII, Radiocarbon, 1978, 20, 469-486. 2

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[40] Follestad, Β. Α., Olsson, I. U., The C Age of the 'Toten' Mammoth, Eastern Norway, Boreas, 1979, 8, 307-312. [41] Hassan, Α. Α., Geochemical and Mineralogical Studies on Bone Material and Their Implications for Radiocarbon Dating, unpublished doctoral dissertation, Southern Methodist University, 1976. [42] Hassan, Α. Α., Ortner, D. J., Inclusions in Bone Material as A Source of Error in Radiocarbon Dating, Archaeometry, 1977 19, 131-135. [43] Hassan, Α. Α., Hare, P. Ε., Amino Acid Analysis in Radio carbon Dating of Bone Collagen, In: Archaeological Chemistry II, p. 109-116, Washington, D.C., American Chemical Society, 1978. [44] Longin, R., New Method of Collagen Extraction for Radiocarbon Dating, Nature, 1971, 230, 241-242. [45] Protsch, R. R. R., The Dating of Upper Pleistocene Subsaharan Fossil Hominids and Their Place in Human Evolution, with Morphological and Archaeological Implications, unpublished doctural dissertation, University of California, Los Angeles, 1973. [46] Berglund, Β. Ε., Håkansson, S., Lagerlund, Ε., Radiocarbondated mammoth (Mammuthus primigenius Blumenbach) finds in South Sweden, Boreas, 1976, 5, 177-191. [47] Haynes, C. V., Bone Organic Matter and Radiocarbon Dating, In: Radioactive Dating and Methods of Low-Level Counting, pp. 163-168, Vienna, International Atomic Energy Agency, 1967. [48] Ho, T., Marcus, L. F., Berger, R., Radiocarbon Dating of Petroleum-impregnated Bone from Tar Pits at Rancho La Brea, California, Science, 1969, 164, 1051-1052. [49] Purser, Κ. Η., Accelerators-The Solution to Direct C Detec tion, In: Proceedings of the First Conference on Radiocarbon Dating with Accelerators, pp. 1-32, Rochester, University of Rochester, 1978. [50] Mast, Terry S., personal communication, 1980. [51] Haynes, C. V., Applications of Radiocarbon Dating with Accel erators to Archaeology and Geology, In: Proceedings of the First Conference on Radiocarbon Dating with Accelerators, pp. 276-288, Rochester, University of Rochester, 1978. [52] Sweeney, R. Ε., Liu, Κ. Κ., Kaplan, I. R., Oceanic Nitrogen Isotopes and Their Uses in Determining the Source of Sedimen tary Nitrogen, In: Stable Isotopes in the Earth Sciences, pp. 9-26, Wellington, New Zealand, 1978. [53] Rennie, D. Α., Paul E. A. Johns, L. Ε., Natural Nitrogen-15 Abundance in a Wide Variety of Soils, Canadian Journal of Social Science, 1976, 56, 43-50. [54] DeNiro, M. J., Epstein, S., Influence of Diet on the Distri bution of Nitrogen Isotopes in Animals, Geochemica et Cosmochimica Acta, 1980, in press. 14


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[55] In an earlier paper [31], the N values for two fractions of this bone was reported as -7.84 and -7.66 per mil. Analytical problems, which were unrecognized during the earlier measure ments, have now been resolved. The average values for whole bone and for the organic extract listed in Table 5 are now considered to better represent the correct values. G. Rao, personal communication. [56] Rau, G., Kaplan, I. R., Taylor, R. Ε., manuscript in prepara tion. [57] Bada, J. L., Schroeder, R. Α., Amino Acid Racemization Reac tions and Their Geochemical Implications, Die Naturwessen schaften, 1975, 62, 71-79. [58] Bada, J. L., Master, P. Μ., Hoopes, Ε., Darling, The Dating of Fossil Bones Using Amino Acid Racemization, In: Radiocarbon Dating, pp. 740-756, Berkeley, University of California Press, 1979. [59] Von Endt, D. W., Techniques of Amino Acid Dating, In: Pre Llano Cultures of the Americas: Paradoxes and Possibilities, pp. 71-100, Washington, Anthropological Society of Washington, 1979. [60] Hare, P. Ε., Organic Geochemistry of Bone and Its Relation to the Survival of Bone in the Natural Environment, In: Fossils in the Making: Vertebrate Taphonomy and Paleoecology, Chicago, University of Chicago Press, 1979. [61] Bender, M. L., Reliability of Amino Acid Racemization Dating and Paleotemperature Analysis on Bones, Nature, 1974, 252, 378-379. [62] Hare, P. Ε., Gil-Av., Ε., Separation of D and L Amino Acids by Liquid Chromatography: Use of Chiral Eluants, Science, 1979, 204, 1226-1228. [63] Berglund, Β. Ε., Hakansoon, S., Lagerlund, Radiocarbon-Dated Mammoth (Mammuthus primigenius Blumenback) finds in South Sweden, Boreas, 1976, 5, 177-191. [64] The assistance of G. Rau and I. R. Kaplan (UCLA) in the stable isotope studies as well as the dedicated laboratory work of Peter Slota, L. A. Payen, and G. Prior (UCR) is gratefully acknowledged. This research was supported by a National Science Foundation grant (BNS-7815069). RECEIVED

August 11, 1981.


Problems in the Radiocarbon Dating of Bone - ACS Publications

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