Edited by DAN KALLUS Midland Senior High School 906 W. iiiinais Midland. TX 79705 RUSSELL D. LARSEN Texas Tech University Lubbock, TX 79409
Archaeological Dating M. W. Rowe Texas A&M University, College Station, TX 77843 Only for the past quarter of a century or so have scientists been makina widesoread use of "absolute" datine techniquesin archaeology, as opposed to the relative agesobkinable through a study of stratigraphic sequencing, for example. Earlier in this Journal, I discussed the use of radioactive dating techniques in geology (1). Here I will discuss hriefly some modern methods used to date archaeological artifacts and other remains. Prior to the Second World War archaeologists had no technique with which to estimate accurately the age of archaeological finds, with the exception of the use of dendrochronology (tree ring dating) and varve studies. Now there are a number of techniques at the disposal of the archaeologists, some based on radioactive decay, some on radiation damage, and some on chemical or physical changes within a sample of interest as a function of time. Nuclear Datlng Techniques There are a t least eight different nuclear dating techniques used in archaeology. These are outlined in Table 1, and each will be discussed briefly. Radiocarbon Dating On December 12,1960, J. Willard Libby was awarded the Nobel Prize in Chemistry for "his method to use 14Cfor age determinations in archaeology.. .." It was noted there that "seldom has a single discovery in chemistry had such an impact on the thinking in so many fields of human endeavor" (2).The interesting history of this important development has been well recorded (3). Neutrons are ejected when cosmic rays bombard the atmospheric atoms in the upper regions of the atmosphere. These neutrons further collide and undergo nuclear capture reactions with other atmospheric atoms. In particular, '4C is produced by the reaction 14N neutron 14C+proton. '4C is radioactive and has a half-life of 5730 years, just the right order for many archaeological measurements of interest. The 14Catoms react rapidly with atmospheric oxygen by the reaction: 14C 0 2 14C02;the "COX mixes with "ordinary" carbon dioxide, eventually becoming distributed throughout the atmosphere and forming an equilibrium with the hydrosphere and biosphere. Thus, because the cosmic ray flux appears to have been fairlv constant over the Dast 100.000 Gars or so, there has been relatively constant'influx of 14c into all living.. organisms during that time and before. .. As long asnn organis~nisalive, constant exchange with the atmosphereoccurs sorhat the amount 0 f ' T per unit rnassof
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Journal of Chemical Education
living carbon matter is in equilibrium with the "C in the atmosphere. When a living organsim dies, there is no further intake of '4C and the amount present at death steadily decays away a t a rate independent of temperature, pressure, and all other conditions. Anderson et al. (4) found that living materials all contain 15.3 disintegrations per minute (dpm) '4C per kg of carhon. Thus in principle, radiocarbons dating is exceedingly simple. The age, t, is given by the decay relationship
where dh'ldt is the decay activity of the 14C in the sample and X is the decay constant for "C. I t is, therefore, only necessary to measure the specific 14C radioactivity of the sample to be dated. For example, if a sample had a specific
Table 1. Nuclear ~ i t i n gTechniques That are Used In Archaeological Applications Technique
Radionuclides of interest
Radiocarbon Conventional Accelerator
"C "C
Time Dependent Quantity Measured
14Catoms decaying
'% aatms remaining
Mher Radioisotopes
Conventional Accelerator
"Be, "Ai. s2Si.W I , "Ca lob, %i. 3SCi."Ca
Atoms decaying Atoms remaining
Thermoiuminescence
'OK. 235.P8U.23%
Luminescence caused by thermal release of trapped electrons originally dislodged by the nuclear energy from natural radioactive decay
Electron Spin Resonance
'OK, "'."U,
Defect electron traps
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Fission Tracks Alpha Recoil Tracks Uranium Series Polassium-Argon
232Th 258U
23% 235.230U.
Chemically etched tracks from fission damage Pits from a-recoil damage
230Th1234U; 234U12S8U Growth of 230Thand decline of "W MK
''Ar dawhter from decay
activity of 7.15 dpm I4C per kg of carbon, then i t is readily seen that half of the initial 15.3 dpm I4C has decayed away. Thus a decay time of one half-life of I4C, 5730 years, is assigned as the age of the sample. Although the method is very simple in principle, the level of 14C is low and verv sensitive~radioaEtivecounters are necessary to measure it; actkity. Other difficulties render dating- a difficult technique which requires skilled operators. Since the inception of the radiocarhon method, there have been thousandsbf radiocarhon ages measured. The impact of radiocarhon dating on archaeology is best demonstrated by the fact that almost all other scientific dating techniques in archaeology show evidence of their reliability by comparison with radiocarhon dating. The technique is applicable to any biological material whose death yields an archaeologicalls meaningful marker of time. Charcoal. wood. bone. leather, textiles, ropes, and fibers are only a few of the materials which have heen used to date archaeoloeical sites. l'ractical considerations limit the effectivenessof radiocarhon dating to a range of 200 up to 40,000 years with desirable sample sizes ranging from 7 g to a kilogram or so, depending on the specific sample and its age. Accelerator Radiocarbon Datlng
Conventional radiocarhon dating measures the numher of I4C atoms that decav. Since there are 109-10'2 more 14C atoms present in a sample which do not decay during a given counting period. an imorovement in efficiencv might he expected ;faone directlymeasures the numhe; of k atoms present, rather than waiting for them to decay. This was recently accomplished by using a particle accelerator as a mass spectrometer to measure the I4C atoms in a sample. The samples are reduced to charcoal which is mounted on the ion source of an accelerator. Then the 14C atoms are ionized, accelerated, and counted as they emerge from the accelerator (5).By use of such a technique great advantages are obtained: (1) the sample size requiredis only 1-15 mg; (2) the accuracy is increased; (3) the range of ages can heextended possibly to 100,000 years; and (4) the time required for a determination is reduced. The obvious disadvantage is for the need of a particle accelerator which is a relatively expensive operation. ~
~
~
~
~~
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Other Radlolsotope Dating Methods
There are a numher of radioisotopes with varying halflives that can he used in a way which is similar in principle to radiocarhon dating. These include 'OBe(tl12 = 1.5 X 106 y), 26Al(t~i2 = 7.3 X 105 y), 3 2 S i ( t l= ~~ 250-700 y), 36Cl(t112= 3.1 X lo5 y) and 41Ca(tl,2 = 1.3 X lo5 s ) . None of these radioisotopes have as direct a connection hetween an arrhaeologirally signiiicant event and the starting of the radionctive chronometer as radiocarhon dating, s o t h a t none of these techniques have the utility of radiocarhon or even some of the methods to he discussed later in this paper. 'OBe and 26A1 have half-lives of about the same length, are hoth produced in the upper atmosphere and circulate as aerosols, as does 32Si. Unlike W , these isotopes show a strong latitudinal variation in their activities. The half-lives of 'OBe and 26A1 are suitable for dating events older than those obtainable through radiocarhon dating. Both of these two isotopes are likely to he of importance mainly in the dating of sediment cores which can then be calibrated against other important stratigraphic information, e.g., changes in flom and fauna, oxygen isotope ratios.and magnetic reversals. Both'"Beand 26A1have been determined hy conventional counting technique and with accelerator mass spectrometry. The short half-life of 32Siseverely limits its utility for archaeology, hut it may prove useful for authenticity measurements. 36CIand 41Ca also have a numher of similarities with one another. Their half-lives are similar, both are probably produced hy neutron-capture reactions in the atmosphere and
both may be useful in dating a similar event, i.e., the fresh exposure of formerly buried rock. Since calcium is a major constitutent in bone, it has a more direct link to events of archaeological significance and hence prohably has more potential for archaeological dating. Neither method has been fully demonstrated yet, however, and there are serious problems to he overcome before one can expect them to he of widespread use. Thermoluminescence( TL)
Pottery fragments are among the more common archaeological remains. The extention of the Ti, dating technique to archaeological material in 1960 added a very useful adjunct to 14Cdating in archaeology (6). Unlike 14Cwhich decreases with age, the T L signal increases with age as illustrated schematically in Figure 1. The natural long-lived radioactivities in the ceramic itself and in the surrounding burial soil equation is deceptively simple, i.e., natural TL age = (2) (TL per unit dose)(dose per year) where natural T L is thr mean glow curve level usually taken ur 400°C, TI, Der unit doso is rhe susceotihilitvof the samole to acquiring TL, which is measured h i exposing the sample to a known dose of radiation and then measuring the "artificial" TL in the sample. The dose per year is evaluated by analyzing for the uranium, thorium, and potassium of the sample and its surrounding soil. The dose is the amount of energy absorbed from radiation per gram sample. Although thisequation is very simple, there are many ~ o & ~ l i c a t i o n a i n the actual dating which are mainly concerned with the detailed mechanism of thermoluminescence and radiution dosimetry. C h e r techniques have bttcn de\,eloped to overcome the difficultirs, however, and TL dates accurate to 5 I 10"' are possible. Unlike the prohlems which affect the accuracy of '4C dating, which have to do with global prohlems, i.e., lack of strict cosmic-ray constancy with time, etc., the prohlems encountered in T L dating are local and deal with the sample itself and the soil which surrounds it. Thus the two methods are complementary to one another in a useful way. Electron Spin Resonance (ESR) Dating
A very new dating technique similar to thermoluminescence was develoned hv. Ikeva . (7). . . The method uses ESR to measure radiation-indured defects in calcites, especially stalactitr, stalagmite. and other cave deoosits. FSR allows 01)servation o f t h e defect electron traps directly by measurement of microwave absorption in a strone maenetic field. The archaeological dose to the sample is evaiuated in a manner similar to TL. The advantages of ESR over T L are: (1) ESR measures the trap concentrations nondestructively, which allows repeated measurement of the sample, thus ~
TL of geological clay
~
Natural TL in pottery
Firing (Kiln, oven.
campfire)
Laboratory Heating
Time Figure 1. Simplified schematic represemation of Setting in TL dating of pottery.
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making direct interlahoratory comparisons possible; (2) sample preparation is far simpler in ESR than in T L where powder size selection is necessary; (3) ESR measurements are easy to make; and (4) ESR is less sensitive to surface effects than is TL. The disadvantage is that ages of about 500-1000 years are generally the minimum that can he made. The maximum age so far is about a million years, which gives the technique a good range. Although new, the plausibility of the method has been demonstrated and ESR dating is a potentially powerful technique to he added to the other techniques presently available for use in archaeology.
niques are auite different. Three situations in which F T dating should have high potential for use in archaeology are: (1) natural glasses or crystals whose formation time corresponds to an activity of archaeological interest, e.g., the Olduvai Gorge problem inst mentioned: (2) man-made elasses, recent &rial in ahich uranium has been add& for coloration, and older material in which uranium is a natural constituent of the raw materials that make up the ceramic; and (3) natural glasses or crystals known to have been reheated. Examples of all these have been done and more applications are expected in the future.
Fission Track Dating
Alpha-Recoil Tracks
Techniques used for dating of geological and archaeological materials using fission-fragment tracks have evolved over the past quarter century. The initial ground work was done almost exclusively by three physicists, R. M. Walker, P. B. Price, and R. L. Fleischer, then a t the General Electric Research Laboratory. Price and Walker ( 8 ) discovered that the damage zone created by the passage of a pair of fission fragments through a mineral could he made visible in an optical microscope by chemical etching. Thus, it became relatively easy to measure the damaee tracks of a fissionine nuclide.Sinck the number of trackswina sample is proportional to the age of the sample (actuallv to the time since the last heating severe enouih to erase tracks) and to the amount of fissioningmaterial in the sample, this is a classical radiometric dating procedure. Although there are three naturally occurring isotopes which undergo spontaneous fission. 235U.23sU. and 232Th. . onlv. 238Uvields a sienificant number of fission events in geological and archaeological samples. Thus a mineral can he dated if enoueh time has elapsed since 11s fnrmntion to accumulete n significant numIwr oi tracks and if the "*lJ contenr can he measurrd. The fission track (FT) technique can also he used as a very sensitive method to determine uranium hv suhiectine " the sample to a thrrmnl-neutrnn irradiation. In samples of very low nge, minerals with hich uranium must hechosrn. The F'r age equation is
Analoeous to the fission track situation,. crvstal damaee is encountered when a heavy nucleus recoils from an a p a r h e emission (12).These tracks, however. are much smaller than the fission tracks and electron micr© is necessary for their detection. Furthermore, not only 23sU hut 235U and 232Thas well contribute significantly to the a particle tracks. In spite of the fairly widespread availability of electron microscopes, there has still been very little application of this technique in archaeology.
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where T = age in years, X, and XE are the alpha and fission decav constants for 238U.res~ectivelv.and io. and rr; are the areadensity of tracks from ihe ~ ~ o n t a n e o i f i s s i of d i 238U and induced fission from neutron irradiation of the 235U in the sample, respectively, d is the thermal neutron flux of the sample irradiation, rr is the cross section for neutron-induced fissionZ35U,and (N235IN23~)is the ratioof those twouranium isotopes a t the present time. The effectiveness and the range of F T dating are illustrated in Figure 2 which shows a comparison of F T ages with ages established by independent means (9).A high uranium glass of < 1 year old, archaeological samples of < 1000 years old, and geological samples up to about a billion years old have been measured with fair accuracy. No other technique has demonstrated so wide a ranee of aee determinations. T o date there have been relat&ely few applications of F T dates in archaeoloev, althoueh the technicwe has been more widely used in geology. o n e interestiniapplication soon after the inception of F T dating was the dating of the Olduvai Gorge area which is important with respect to hominid origins in East Africa. The early 4"K-40Arage (10) was under suspicion. This age, 1.8 X lo6 years, was more than twice the expected value. The General Electric group, along with Leakey ( 1 1 ) conducted F T measurements on volcanic glass a t the Olduvai Gorge site from the same deposit previously dated by 40K-40Ar.The F T age was found to he 2.03 f 0.28 X lo6 years, confirming the age determined by 40k-40Ar.The complementary use of 40k-40Arand F T dating is very instructive as the possible sources of error in the two tech18
Journal of Chemical Education
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Uranium Series Dating
When CaC03 is precipitated from natural waters, as in stalactites, stalagmites, etc., uranium is a trace contaminant which is coorecioitated with the Ca2+. Whereas uranium is . . easily transported in solution in groundwaters, thorium, and protactinium ~reciuitateout and are t r a ~ o e din soil. Thus. uranium is pr&ipi&ed in CaC03 deposits free of two of i& long-lived daughters, 230Th(tl12 = 75,200 y) and 231Pa(t,n = 32.500 v). since carbonate deposit therefore contains no23QTh initially, its growth can he noted after time, t, and an age equation can he written:
a
%34
'
%1
L
where A230 and Xpaa are the decay constants for 23Th and 234U,respectively.
1
10'
1O6
1O8
FISSION TRACK AGE (years) Figure 2. Comparison of ages found by fission-track dating wilh those established by other means. me samples less than 200 years old are man-made; the alder ones are geological (from ref 9).
Similarly the activity of 231Pais time dependent, so that
where X.m is the decav constant of 231Pa. Usual uranium concentrations in carbonate deposits are between 0.1 and 2 ppm, which gives a viable dating range of 10,000 to 400,000 years. Although uranium series dating has been applied primarily to carbonate materials rather than bones, i t was applied first to fossil bones by Cherdyntsev (13) in 1956 and the method has been advanced considerably since the late 1960's by Szabo and coworkers (14). The technique yields reliable ages in many cases, but in others contamination has been a serious problem. 210Pb is also a member of the uranium series, but with only a 22-y half-life, its use has been restricted to authenticity studies of lead-containing artifacts (15).
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Racemization studies were suggested in the late 1950's and early 1960's to provide a new method of dating fossil materials (16). The technique holds considerable promise for the dating of ancient bone samples. Both L- and D-amino acids are found in fossil materials and the D/L amino acid ratio increases with time, although the time necessary to reach the equilibrium D/L ratio varies from one amino acid to another as well as to the particular climatic and environmental conditions of a particular site. Aspartic acid is the amino acid most commonly used in the racemization dating of bone. The reaction is k
L-asparticacid r D-aspartic acid
(6)
where k is the first-order rate constant for the reversible conversion of L- t o D-and vice versa. The racemization age equation is rather complicated (17):
PotassiumArgon Dating
Potassium-argon dating was discussed in detail in the paper on geological dating techniques reported earlier in this Journal (I). The aoplication of 40K-40Ardating to archaeology differs from &ological dating in that samples of archaeological interest are almost invariably much younger. Hence, minerals with high potassium content must-be sought and great care must be taken to optimize the argon sensitivity when dating almost all archaeological events of interest. Chemical Dating Techniques
Bone is comnosed of two maior structural com~onents -one organic, the other inorganic. There are compositional differences due to species, age, sex, etc. Typically the elemental composition is as follows: calcium, 20-22%; phosphorous, 10%;the organic component, 10%; H20, 10%; nitrogen, 6%; fluorine, trace; uranium, trace; and others of less interest here. After the death of an organism, chemical alteration occurs-fossilization sets in. The specific changes vary according to physical, chemical, and biological factors of the specimen and its environment. During fossilization, inorganic elements can be added or taken awav. Bone has been shown to be a useful material for dating via chemical changes. Several chemical datine methods have been used with some success and are summarized in Table 2.
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Amino Acid Racemization
Biological pathways leading to the formation of amino acids which are present in the proteins of living organisms, especially higher organisms, produce only the levorotatory optical isomer, the L-enantiomers. However, after the death of an organism, these L-amino acids undergo slow change (racemization) to produce the corresponding D-amino acids, tending toward a 50.50% mixture of the D- and L-forms. Table 2.
Chemical Changes Used In Archaeofoglcal Datlng Methods Time-Dependent QuantiN Measured
where t is the time in years, CD/CL is the aspartic acid enantiomeric ratio in the bone sample, and the t = 0 term is 0.14 in modern bone. In general, a rate constant, K, varies with temperature as given by the Arrhenius rate equation. = Ae-EIRT
where A is the Arrhenius constant, E is the energy of activation of the reaction, R is the universal gas constant, and T is the temperature. The racemization rate constant, k, follows the same exponential law. Thus, a primary problem with amino acid dating is that k in eq. 6 varies with temperature. An error of Z°C can introduce an error of 50% in age! Unfortunately temperature fluctuations of that order or more are well known throughout the past million years. However, in locations where the temperature is not too variable, e.g., in the deep ocean or caves, ages consistent with radiocarbon dates have been obtained. The accuracy of amino acid racemization dating, even under the best of conditions, does not yet compare with radiocarbon dating. Obsidian Hydration Dating
In many areas of the world, obsidian is as abundant as pottery and potentially as significant for dating. The chemical dating of obsidian artifacts is based on the fact that a freshly exposed surface of obsidian absorbs water from its surroundings to form a hydration layer, not visible to the naked eye (18). Most obsidians contain 0.1-0.3% water initially. Hydrated zones contain -3.5% water. The diffusion front of the water absorption is sharp, varying only by 4 . 0 7 pm in depth. The greater water content causes the density of the hydrated layer to increase, introducing mechanical strain which can be seen under polarized light. The phenomenon appears as a measurable luminescent band. The depth of hydration seen on any obsidian artifact is representative, therefore, of the amount of time that has elapsed since the artisan prepared the object. In order for obsidian hydration layers to yield chronometric ages, the rate of hydration must be calculated. Theoretically the movement of water into obsidian is given by Ficke's law of diffusion X2
Amino Acid Racemization
Obsidian Hydration Fluorine Uranium Nitrcgen Thermal Analysis
The change of the initially 100% L form to 50.50% and D forms of the amino acld. me increase in thickness of the hydrated layer of obsidian Increase in fluorine in sample Increase in uranium in sample Decrease in nitrogen in sample Parameters derived from thermp gravimetric curve
(8)
= kt
(9)
laver thickness, k is the diffusion coeffiwhere w.. = hvdration . cient, and t is the time. As with aminn acid racemization, the constant k issrronalv dependent on temperature ~Arrhenius equation). But theiimp&ature is unfortunately not the only variable which affects hydration rates. Obsidians of different compositions can have different diffusion rates. Empirical studies involving hundreds to thousands of obsidian hydration measurements are necessary to provide an adequate basis for ages thusly calculated. Volume 63
Number 1 January 1986
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Elemental Content Changes The oldest among the chemical technique of dating archaeological materials is fluorine dating which is based on the fact that ground water with fluoride ion reacts with the hydroxyapatite of the bone to form fluoroapatite (19).Obviously, the rate of the reaction is a function of the concentration of the F- ion in ground water, the chemistry of the soil surrounding the bone, the amount of contact with ground water, temuerature. etc. Thus.. verv. old bones in a F--noor site may c;ntain less fluoroapatite than a younger honiin a site rich in F- ion. Furthcrmorr the formation of CaCO? can seal a bone to the further fluorination of the hydroxyap&ite. Nonetheless, fluorine dating has been shown to be of use in providing relative ages within a particular area. I t is not possible to compare fluorine ages between different sites. Dates obtained from fluorine analysis should be used only with great caution. Uranium dating (20) is very similar in principal t o fluorine dating. The uranium content in buried bones increases as the bone stays in contact withU-bearing ground water. As with fluorine dating, uranium contents can he used to distinguish relativelv older from vouneer bones a t the same site but not between different s&s. Algain caution is necessary. The interiors of bones contain oreanic material. orincioally collagen, which contains suhsta&ial nitrogen.The c&agen disappears only slowly by decay after death. This means a loss in nitrogen with age and measurement of this loss provides the basis for nitrogen dating (21). As with all elemental techniques, the principals and the limitations are very similar to fluorine and uranium chemical dating. The loss in nitrogen (collagen) goes faster a t first (for about 100 years) and much slower thereafter. Only relative ages from the same site are meaningful. Thermal Analysis Dating Another very recent chemical dating method is that of fossil age determination by thermal analysis (22). I t is based on the fact that both inorganic and organic chemical compositions regularly change in a given geological environment as a function of time. The study by Szoor (22) concentrated on the apatite-collagen system of vertebrates. The ages are calculated by the use of three empirical equations, each for use in a different age regime (Holocene, Pleistocene, and Pliocene) using data taken from thermogravimetric analyses. Being a chemical method, it suffers from the same difficulties encountered for those methods discussed earlier. Although of utility, all of the chemical dating methods must be used with great caution and with careful consideration of all available geological and archaeological information. Independent corroboration of the chemical ages is desirable in all cases. Archaeomagnetlsm There is also a dating method based on changes in a uhvsi. . cal property, i.e., magnetic parameters. The earth's magnetic field is reasonably umell represented by a hypothetical bar maenet. The values of three maenetic . orooe&ies-declination, dip or inclination, and intensity-change with time and these changes are termed secular variation. Secular variations have been reported historically for London, Paris, and Rome over the past four centuries. Besides this and other written records, secular variation information is also stored in baked clay (or rocks) as they cool. The archaeological information is only retrievable if the position of the clay is known a t the time of firing. This information is often best retained in kilns, fireplaces, and campfire sites. There are a numher of rather se\.ere limitations in the use of archaeomagnerism for dating. First there is a need for a
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calibration curve for each region of the world -500-1000 miles across. Thus, many years of work is necessary involving other dating techniques simply t o establish the calibration curve. Secular variation curves have been established for varying time a t only a few regions in the world. Thus far, only England, France, Germany, Japan, and the southwestern United States have received much attention. Secondly, the same values of secular variation occur more than once in the past and, therefore, do not yield unambiguous ages. Thirdly, there are periods of time when the chanee in secular variation is slow and therefore not sensitive for &e determination. Fourth, some movement or marnetir distortion has occurred since the implantation of the magnetization introducing error in the age assignment. Finally, in order to sample as comprehensively as is necessary to establish reliable ages, damage or even destruction of the site sample is often unavoidable. In spite of these limitations, many useful archaeological results from archaeomaenetic studies have been obtained. Furthermore, even if a magnetic date is unobtainable from a burned structure, it is nonetheless a source of unioue eeophysical information, providing the declination, the inclination, and the intensity of the maenetic field at a time nast in the earth's history. ~~
~~~
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Summary The development of "absolute" dating techniques, especially radiocarbon, has been of tremendous importance in modern archaeology. All the techniques discussed here have contributed measurably to our archaeological knowledge and will certainly continue to do so in the future. Acknowledgment Thecomments and criticismsof Mark Ttrbey,TexasA&M University, are gratefully acknowledged. Literature Clted (1) R0we.M. W. J Cham.Educ.,submitted (L984). (2) Nobel Foundation, "Nobel kcturer, Chemistry 19421962"; Ekevier: Amsterdam. 1964; PP 587-592. (31 Libby. W. F. '"&dimarbon Dating." 2nd ed.: U, of Chicapo: 1967; In "Radioactive Dating and Lm-Level Counting." I.A.E.A.: Vienna. 1967; pp 3-27; In "RadiocarbonVaristianasndAbsoluteChronology";Olsran I.V..Ed.: Almquist, and Wiksell: Stockholm, 1970:pp 629-6fi;Phil. Tram. Re". Soc.Lod. A l970,269,1:In"Pra. 8th Int. Can1 on Radiocarbon Dsting"; Raftax, T A.; Grant~Taylor,T.. Eds., Roy. Soc.: New Zealand, 1972: pp rruii-rliii: Ksmen, M. Seienee 1963.140,5&i. (4) Anderaon, E. C.; Libby, W. F.: Weinhause, S.; Reid, A. F.; Kirschcnbaum. A. D.: Gr-, A. V. Science 1947,105,576. (5) Bennet, C. L. Science 1977.198, 508; Ndaon, D. E.: Kortelinp, R. G.; Scott, W. R. Seiener 1117. l.W SO7 (6) Grog1er.N.; Houtermans,F.G.:Stauffer,H.HoB.Phya.Aelo.1960.33,595:Kennedy, G. C.; Knopff, L., A r c h a d 1960,14 147. (7) Ikeya, M. Nature 1975,255.48. (8) Price. P. B.: Walker. R. M. J. Aool. Phva. 1962.33. 3407. ~
1131 (14) (15) (16) (17) (18) (19)
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Cherdvntaev..V. Sou. Arkheol. 1956. ZI.64 For review see Szabo, 8. J. A n t . Alp. Res. 1980,12,95. Keisch. B. Scisnee 1968,160,431. See Hare, P.H.M w . A p ~ Sci. l Centerfor Arch. 1974,10, 4 fora hiatorieal rwiew. Bada. J. L.;Schroeder,R.A.EarthPlonet. Sei.Leti. 1972,15,1. Friedman. I. L.: Smith. R. L. Amer Anti* 19W.25.476. Middlefon,J.Proc. Gaol. Soc.Landon 18U.4,431;CamoLA..Comp.rend. 1892,115, 337:Carnot.A.Arner. Mines 1893.3 155.
General References No attempt has been made to give references to the recent publications in the various areas of archaeological dating. Rather I tried to give credit to the persons responsible for discovery and early development of the techniques. For further reading, with more up-to-date references. the reader is referred to the following books: Fleming. S. "Dating in Alchseology." St. Martin's: New York, 1977. Goiter. 2. '"Archewlogicsl Chemistry," Wiley: New York, 1980. . C.. Ed. "Qusfernary Dating Methods." Elsevier: New York, 1984 Mahaney, W Michela, J . W. "Dating Method8 in Archaeology." Seminar: New York.1973.
