CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY

340 INTRODUCTION: 348 ISOTOPIC ANALYSES IN THE LABORATORY PREHISTORIC DIET AND ISOTOPES IN ARCHAEOLOGY 341 WHY IS ARCHAEOLOGICAL CHEMISTRY IMPORTANT? 351 ARCHAEOLOGICAL THINKING: CLIMATE, ISOTOPES, AND VIKINGS IN GREENLAND CHEMISTRY IN ARCHAEOLOGY ANCIENT MIGRATION AND ISOTOPES 342 INSTRUMENTATION IN ARCHAEOLOGY

343 PROTECTING THE PAST: THE ETHICS OF 354 IN FOCUS: THE FIRST KING OF COPAN, DESTRUCTIVE ANALYSIS A CLASSIC MAYA CENTER IN HONDURAS

NEUTRON ACTIVATION ANALYSIS (NAA) 355 ORGANIC RESIDUES IN ARCHAEOLOGY INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (ICP-MS) 356 IN FOCUS: TRACES OF CHOCOLATE IN CERAMIC VESSELS FROM THE NORTH AMERICAN 344 SCIENCE IN ARCHAEOLOGY: SOUTHWEST THE ARCHAEOLOGICAL CHEMISTRY LABORATORY AT ARIZONA STATE UNIVERSITY 357 IN FOCUS: ZOOLOGY BY MASS SPECTROMETRY GAS CHROMATOGRAPHY-MASS SPECTROMETRY (GC-MS) X-RAY DIFFRACTION (XRD) 357 CONCLUSIONS 346 ELEMENTAL ANALYSES 358 ARCHAEOLOGY PROJECT: ISOTOPES AND PREHISTORIC DIET

347 IN FOCUS: OBSIDIAN SOURCES AND TRADE IN THE ANCIENT NEAR EAST 359 STUDY QUESTIONS CERAMIC ANALYSIS METAL ANALYSIS 359 FURTHER READING INTRODUCTION: ARCHAEOLOGY the opportunity to acquire this piece came to Furthermore, the Getty kouros and the torso had IN THE LABORATORY the attention of the J. Paul Getty Museum in dif erent surfaces. California in the late 1980s, excitement was high. T e story of the Getty kouros is a classic Archaeological chemistry takes a variety of direc- T e statue was accompanied by documents that example of archaeometry in action, where art tions in the study of the past. Two important indicated its origin and authenticity.T e museum and science meet. T ere is no doubt that the applications are the authentication of ancient checked with the governments of Greece and Getty statue is a kouros. To most viewers, it materials and the determination of place of origin Italy to ensure that the statue had been legally is beautiful: it is art. T e question, however, (provenience). A number of elements and iso- obtained. T e Getty also requested samples of is whether it is ancient art or a more recent topes have been used in the investigation of stone from the statue for analysis. Preliminary forgery. While most art historians and archae- provenience. Lead isotopes, for example, have studies pointed to the island of T asos [THOSS- ologists believe the statue is a fake, the scientists been used for many years in Europe to determine os], an ancient quarry site, as the source of the involved believe it to be authentic. T e status of the origins of bronze artifacts. Copper and tin, marble. Moreover, the surface chemistry of the the Getty kouros remains a mystery. T e infor- the major components of bronze, occur in limited stone revealed a calcite crust that was thought to mation plaque with the statue at the museum areas and do not appear together in most cases. require a long period of time to form. today reads “Greek, 530 bc, or modern forgery.” Both contain small amounts of lead, of which T e Getty purchased the kouros for approxi- T e story of the kouros also raises an important the isotopes vary in the di f erent sources for mately $8,000,000 and put it on display while issue of ethics in archaeology. Should museums copper and tin, allowing them to be identif ed. experts—art historians, conservators, archaeo- purchase artifacts and monuments that are part T e trade and transport of these raw materials logists, and archaeometrists—studied the piece. of the heritage of other nations or peoples? T is and f nished products across the European con- Opinions regarding its authenticity were divided. question of who owns the past is addressed tinent is reasonably well documented, thanks Why was it in such good condition, and why so further in Chapter 16. to archaeological chemistry. T ere are many white? T e styles of depicting the hair and feet T is chapter is an introduction to archaeo- other uses of archaeological chemistry as tools were dif erent: the wig-like hair is normally found logical chemistry, the application of chemical to study the past, and new applications appear around 600 bc, while the arrangement of the feet and physical methods—hard science—to the regularly. T e investigation of the chemistry of should date to 525 bc. Would an ancient sculptor study of archaeological materials; archaeo metry the living f oors at Keatley Creek, for example, combine several styles in a single piece? Was the is another term for such investigations. In addi- was discussed in Chapter 9 (see p. 220), while quarry at T asos in operation when this statue tion to marble statues, archaeological chemists the use of carbon and nitrogen isotopes has been was purported to have been made? study a wide variety of materials including mentioned in several previous chapters. In the T en, in the early 1990s, evidence came ceramics, bone, lithics, soils, dyes, and organic following section we describe one of the more forth that the authenticating documents were residues. T is chapter of ers some information famous cases of authentication in archaeology: forgeries. Moreover, a clearly fake marble torso on instrumentation and archaeological chemistry the Getty kouros. very similar to the Getty kouros was found. T e laboratories, the questions asked, and exam- A kouros (Greek: “youth”) is a stone statue of debate regarding the statue intensif ed. New tests ples of important studies. Various aspects of a nude, muscular young male, carved during the were performed on the museum piece as well archaeological chemistry are described in sections Classic period of Greek civilization between the as the forged torso, but were not conclusive. on elemental analyses, isotopic analyses, and sixth and third centuries bc. A kouros [KURH- Scientists were able to show, however, that the organic analyses. Several examples are included, oss] was an artistic manifestation of the Greek marble torso had been treated in an acid bath to such as obsidian sourcing in the Near East, the worldview that emphasized youth and male simulate aging. Analysis revealed that the surface use of isotopes to document the diets of early beauty. T e poet Simonides (c. 556–468 bc) may of the Getty kouros was a complex compound Greenlanders, and the birthplace of a Maya king. have been referring to a kouros in the late sixth (calcium oxalate monohydrate), not a simple Various kinds of residues are the focus of most century bc when he wrote, “In hand and foot and calcite (calcium carbonate), with characteristics organic chemistry in archaeological chemistry, mind alike foursquare/ fashioned without f aw.” that could not be duplicated in the laboratory. and are discussed toward the end of the chapter. T e statue in the photograph is 2.25 meters (7 ft 4 in.) in height and has several features that are characteristic of kouros statues, which have variously identif ed as gods, warriors, or WHY IS ARCHAEOLOGICAL CHEMISTRY IMPORTANT? victorious athletes. T e hands, for example, are balled into f sts and are held along the body. T e hair is arranged in a regular grid of vertical and Archaeological chemistry, and archaeometry prehistoric materials). Archaeometric studies can horizontal lines. T e feet are placed with the left more generally, is primarily concerned with (1) tell us about subsistence and diet, exchange and foot forward. T e faces of these statues are very identifi cation (determining the original material trade, residence, demography, status, and many distinctive and appear to depict individuals in of an unknown item); (2) authentication (verifying other aspects of prehistoric human behavior and life-like portraits, as opposed to a generic human. the antiquity of an item, often associated with organization. The goal of archaeological chemistry, T e eyes are wide open and the mouth is formed works of art); and (3) characterization (meas- in common with all analysis in archaeology, is to in a serene, closed-lip smile. uring the chemical composition of a variety of learn more about the human past. T ere are only a dozen examples of such f gures in good condition in existence. When

CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 341 CHEMISTRY IN ARCHAEOLOGY core of an atom and have about the same weight. Neutrons have no electrical charge; protons have P ROTECTING THE PAST Archaeologists are often found in the labora- a positive charge. Electrons spin around the core tory. As we have seen in previous chapters, there of neutrons and protons with a negative electrical PROTECTING THE PAST: THE ETHICS OF DESTRUCTIVE ANALYSIS are laboratories for studying faunal remains, charge and a very small mass. Atoms vary in the laboratories for archaeobotany, and laboratories number of protons and neutrons they contain, for spreading out artifacts for analysis. T ere resulting in dif erent atomic weights; these dif- An important concern in instrumental analysis is the condition In archaeological chemistry, scientists must balance the are also laboratories where archaeologists and ferent weights make up the ninety-four chemical of the sample, requirements for preparation, and whether importance of protecting and preserving the past for the future physical scientists investigate the chemical prop- elements in nature. the technique is destructive or non-destructive. Many instru- with the importance of learning as much as we can about our erties of remains from the past. T ese are wet T e atomic number of an element is the ments require destructive sample preparation in the form of a common human heritage. New developments in instrumenta- labs with chemical fume hoods and a variety of number of protons in the nucleus.Isotopes of an powder or liquid. For example, samples must be converted into tion are allowing archaeologists to extract information about scientif c instrumentation. element are slightly dif erent atoms of the same powders for NAA and XRD, into liquids or solids for ICP-MS, the past from smaller and smaller samples, which mini- is a general term element; they have the same atomic number, and gases for GC-MS. This is an important consideration to mizes the destruction of priceless artifacts and archaeological that includes non-instrumental areas, such as but dif erent numbers of neutrons. Ions are bear in mind, as very rare or valuable artifacts and materials materials. In addition, some instruments with larger sample faunal analysis, , and human electrically charged atoms that have lost or should not be subjected to damaging analytical methods. chambers can perform non-destructive analyses. osteo logy. Archaeometry is the measurement of gained electrons. the chemical or physical properties of an arti- Every substance on earth is made up of combi- fact, and technically includes dating methods, nations of these ninety-four elements. Am olecule remote sensing, and ancient DNA (aDNA), but is a combination of atoms held together by bonds NEUTRON ACTIVATION ANALYSIS these f elds tend to pursue a separate identity. (for example, water—H2O—is a combination T e basic requirements for NAA are a source (Physicists, for example, are usually responsible of two hydrogen atoms and one oxygen atom). (NAA) of neutrons, instrumentation for detecting for dating laboratories, while geneticists are the Compounds are combinations of elements in gamma rays, and information about the reactions experts on aDNA.) Archaeological chemistry, a either organic or inorganic molecules in nature. Neutron activation analysis is an instrumental that occur when neutrons interact with nuclei. part of archaeometry, involves the investigation of Organic compounds make up the tissues of method for measuring elemental concentrations Although there are several possible sources for the inorganic and organic composition—elements living organisms and have the element carbon as in a wide variety of samples. Ceramics and various neutrons (reactors, accelerators, and radioisotope and isotopes, molecules and compounds—of a base. Inorganic compounds do not normally kinds of stone are common archaeological materi- neutron emitters), nuclear reactors with high archaeological materials. T e phrase molecular contain carbon. als analysed using NAA, but since samples must f uxes of neutrons from uranium f ssion of er archaeology is sometimes used to refer to the Over the last sixty years, many new ideas, be ground into powder for analysis, this method is the best sensitivities for most elements. For this organic component of archaeological chemistry, instruments, and procedures have been added to destructive. Neutron activation involves exposing reason, facilities for NAA are somewhat limited in and particularly to the investigation of aDNA in the tool chest of what is now called archaeological 15.2 a sample to a burst of neutrons that causes many number and accessibility. In addition, problems plant and animal remains (including humans, as chemistry. T e evolution of both methodology Basic components of ICP-MS. elements in the sample to become temporarily with waste disposal are resulting in the closing Samples are ionized in the plasma we saw in Chapter 14). and instrumentation has permitted more detailed and moved through the entrance radioactive. T ese radioactive elements decay of some research reactors. To appreciate how archaeological chemistry descriptions of the composition of a variety slit and toward the detector by a into stable ones by giving of gamma rays, which works, it is necessary to understand the basic of materials, be they geological, biological, or magnetic fi eld that separates the have energy levels specif c to dif erent elements, atoms by weight. The detector 15.1 tenets of how matter is constituted. All matter archaeological. Today, a number of innovative counts the atoms of different allowing many elements to be identi f ed and INDUCTIVELY COUPLED PLASMA- Basic diagram of an atom with is composed of atoms. Atoms have three major approaches and techniques provide exciting new weights that arrive. measured simultaneously. MASS SPECTROMETRY (ICP-MS) neutrons and protons in the nucleus and an electron moving components: neutrons, protons, and electrons information about the past. around the nucleus. (f g. 15.1). Neutrons and protons make up the ICP-MS is a widely used technology that employs Magnetic a superheated plasma source to generate ions and sector Electrostatic INSTRUMENTATION analyser a mass spectrometer to determine the mass of Nucleus the atoms that are carried to the target f( g. 15.2). containing protons and Archaeological chemistry (or archaeometric) labo- T e combination provides an ef cient, general- neutrons ratories utilize a wide range of instruments and purpose instrument for the analysis of a wide equipment. Four commonly used instruments are variety of materials. ICP-MS is a standard tech- described in this chapter, each based on dif erent nique for the measurement of trace elements, Electron scientif c principles: neutron activation analysis Entrance slit and can record elemental concentrations to ppb (NAA), inductively coupled plasma-mass spec- Exit slit (parts per billion). T e method is destructive, but Proton trometry (ICP-MS), x-ray dif raction (XRD), almost anything that can be put into solution

and gas chromatography-mass spectrometry Ion optics can be analysed by ICP-MS. T e addition of a Neutron (GC-MS). (Another important instrument, laser as an ion source allows the analysis of solids. the scanning electron microscope (SEM), was A wide range of archaeological materials have discussed in Chapter 12.) T ese instruments Slide valve Detector been analysed by ICP-MS including bone, ceram- Interface Electrons moving measure the composition of various kinds of ics, stone, metals, and glass. In a typical application, around nucleus materials. Each technique has advantages and samples are placed in solution by digestion in acid. disadvantages for dif erent archaeological materi- T e solution is sprayed intof owing stream of inert als, as described below. Plasma argon gas and carried to a torch that is heated to

342 / PART 3 ANALYSIS AND INTERPRETATION CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 343 6,000 degrees Celsius (10,800°F; the temperature the mass. T e amount of most elements present of the surface of the sun). In this plasma, the gas in the original material can be measured in just SCIENCE IN ARCHAEOLOGY (CONTINUED) and sample are ionized into their atomic constitu- seconds, even at low concentrations (f g. 15.3). ents. In the ICP-MS instrument, positive ions By combining other instruments with an in the plasma are magnetically focused through ICP-MS, even smaller archaeological samples a mass spectrometer to a collector that records can be analysed and even smaller parts of an atom there are three ICP-MS instruments can be measured. For example, a multi-collector for elemental analysis and the isotopic 15.3 ICP-MS (MC-ICP-MS) can be used to measure analysis of heavy isotopes (such as The ICP-MS in the Laboratory for Archaeological strontium), as well as two mass spec- Chemistry, University of Wisconsin-Madison, operated the isotopes in a sample, as discussed later in by T. Douglas Price (standing) and James Burton. this chapter. trometers that can be used to analyse light isotopes, such as carbon, nitrogen, and oxygen (fi g. 15.5).

SCIENCE IN ARCHAEOLOGY THE ARCHAEOLOGICAL CHEMISTRY LABORATORY AT ARIZONA STATE UNIVERSITY

15.5 Research scientist Gwyneth Gordon The Archaeological Chemistry Laboratory at Arizona State Honduras, Ireland, Mexico, Niger, Peru, Spain, Turkey, and the prepares to put a sample on the MC-ICP-MS University is one of a growing number of archaeometric labo- United States. to measure strontium isotopes. ratories in the United States. Founded in 2005 and directed The Archaeological Chemistry Laboratory has one large by Kelly J. Knudson, the laboratory is a center for research room for research and teaching. This is a wet lab where and training in chemical analysis of archaeological materials. archaeological bone, enamel, soil, plant, and rock samples Research in the Archaeological Chemistry Laboratory are prepared before analysis (fi g. 15.4). The sample prepa- usually involves studying the composition and source of dif- ration area is dedicated to processing samples and includes GAS CHROMATOGRAPHY-MASS ferent kinds of materials to answer archaeological questions a fume hood, furnaces, a system for deionized water, light SPECTROMETRY (GC-MS) about past human behavior. Research methods involve the microscopes to examine samples microscopically, balances elemental and isotopic analyses of teeth, bones, ceramics, for weighing small samples, drills and grinding equipment, T e use of a gas chromatograph-mass spectro- and sediments. Research questions include past diet, human and necessary glassware and chemical supplies. Funding meter (GC-MS) has become standard practice migration, interaction and trade, and the identifi cation of for the laboratory comes largely from the National Science in the analysis of organic compounds (f g. 15.6). activity areas on prehistoric living fl oors. The Archaeologi- Foundation and other grants. T e liquid sample is f rst converted to a gas. cal Chemistry Laboratory is involved with research projects Student training is one of the most important things that T e gas chromatograph separates the hundred on fi ve continents, and hundreds of new samples arrive takes place in the Archaeological Chemistry Laboratory. Each 15.6 of molecules present in the sample in a long each year from all over the world. Collaborative activi- semester, up to twenty undergraduate and graduate students The basic components of a gas chromatograph- column containing a solid that slows some of ties include projects in Argentina, Armenia, Bolivia, Chile, work in the laboratory on their own research projects. While mass spectrometer (GC-MS). An archaeological sample is converted to gas and introduced into a the molecules more than others. T e molecules most of these students attend Arizona gas chromatograph, which separates molecules by then exit sequentially from the chromatograph State University, some come from other weight. Then, molecules are ionized and sent through a and pass into a mass spectrometer with a detector universities in the United States and magnetic fi eld to separate by weight, which is measured by a detector. Output graphs (below) show the results of that registers a peak for each type of molecule. around the world. The Archaeological the gas chromatography and the mass spectrometry. T e GC-MS produces a spectrum of the weight Chemistry Laboratory is also where and amount of the various molecules present. Knudson teaches hands-on courses in T ese spectra are compared with known materials laboratory techniques. Sample Ionization in order to make identif cations. Samples are analysed using mass introduction GAS CHROMATOGRAPH spectrometers in the W. M. Keck Foun- Magnetic fi eld dation Laboratory for Environmental X-RAY DIFFRACTION (XRD) Biogeochemistry. In this laboratory, X-ray dif raction is used to obtain structural and compositional information from crystalline MASS SPECTROMETER materials, and is an important technique in the 15.4 f eld of material characterization. (Solid matter In the Archaeological Chemistry Laboratory, Gas chromatograph Mass spectrum can be either amorphous, with the atoms arranged Kelly J. Knudson (left) works with undergraduate student Kate Spencer. in a random way, or crystalline, where the atoms Light microscopes are used to examine Gas Detector are arranged in a regular pattern; about 95 percent archaeological bone samples. fl ow of all solids are crystalline.) In archaeology, XRD has been used mostly to identify the minerals Time Mass present in ceramics, rock, and sediment samples.

344 / PART 3 ANALYSIS AND INTERPRETATION CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 345 Focus When X-rays are directed at crystalline materi- als, they are scattered in a systematic pattern by Scattered- IN FOCUS radiation the regular arrangement of the atoms (f g. 15.7). diaphragms Aperture Dif erent kinds of material with dif erent arrange- OBSIDIAN SOURCES AND TRADE IN THE ANCIENT NEAR EAST diaphragm Detector ments of atoms produce distinctive scatter, or dif raction, patterns. XRD directs an X-ray source at a powdered sample and measures the 15.9 X-ray tube Two obsidian cores and two blades. This glass-like stone produces very pattern of dif raction that results. T at pattern sharp edges and was a highly desired raw material in prehistory.

Detector is compared to a large database of patterns from Sample diaphragm known materials to identify the sample. Using XRD, scientists can determine the crystal struc- Neutron activation analysis (NAA) is commonly used in tures of metals and alloys, minerals, inorganic provenience studies of obsidian. The sources of obsidian in compounds, polymers, and organic materials, as Southwest Asia, the Mediterranean, North America, Mexico, well as crystal size and orientation and chemical and elsewhere have been examined using NAA. Most of the composition. Finally, one of the advantages of obsidian in Southwest Asia comes from sources either in the XRD is that portable instruments are available, mountains of Turkey or in northern Iran, both outside the Measuring circle making studies possible in museums and the Fertile Crescent. f eld (f g. 15.8). The identity of the sources of obsidian found at early Neo- 15.7 lithic sites in the Near East provides information on both The diffractometer beam path and detector. the direction and intensity of trade (fi g. 15.10). Sites along ELEMENTAL ANALYSES Mediterranean coast generally obtained obsidian from Ana- tolia, while sites in the eastern part of the region used the Elemental analysis is a major part of archaeomet- Armenian obsidian. The percentage of obsidian in the total ric research and is used for a variety of studies, Obsidian is a translucent, hard, black or dark green glass fl aked stone assemblage at these sites indicates that places including authentication and characterization. that is produced during volcanic eruptions when moltensilica closest to the sources used a great deal of obsidian, while T e elemental composition of a material is fl ows out of a volcanic core and hardens into this material. those farthest away had only a small amount available. At the often a specif c signature that can be repeatedly It is therefore available from only a few sources, limited by site of Jericho, for example, 700 kilometers (435 miles) from recognized, so the elemental composition of proximity to volcanic terrain and the chance formation of a the Turkish sources, only about 1 percent of the stone tools archaeological items has been used for years as silica fl ow. In the past, obsidian was highly sought by prehistoric were made from obsidian. a tool to determine provenience. T e elemental makers of stone tools, and was often traded or exchanged over composition of a variety of materials has been long distances, sometimes hundreds of kilometers or more. Obsidian, in common with glass and fl int, fractures easily and studied, including lithic, metal, ceramics, and 15.10 sediments. Lithic, metal, and ceramic studies are regularly, creating very sharp edges (fi g. 15.9). The location of obsidian sources and samples in the early Neolithic of Archaeologists can fi ngerprint different fl ows of obsidian by Southwest Asia. Major rivers shown on the map are the Nile, Tigres, described below, while soil chemistry studies are and Euphrates. Two major obsidian sources are shown in Anatolia and described in Chapter 9. analysing minor differences in the chemical composition of the two in Armenia. The distribution of obsidian from these sources is seen material, allowing pieces found elsewhere to be traced to the at settlements across the area. The distributions are largely separate places where they originated. This procedure relies on what with the exception of one site where obsidian from both source areas is found. Note also the Anatolian obsidian found on the island of Cyprus. LITHIC ANALYSIS is known as the provenience postulate, which states that the chemical differences within a single source of material must 500 km T e geological sources of a variety of stone be less than the differences between two or more sources BLACK SEA of the material. In principle, this means that if a source is Source materials have distinctive elemental signatures. Settlement with obsidian Finds of these materials at sites some distance chemically distinct, pieces removed some distance from the from the original sources can help archaeolo- original source share that same chemical signature and can N gists study trade and interaction if the sources be identifi ed; that is to say, the provenience or place of origin ANATOLIAN can be determined. An example of such a study of the piece can be determined. The provenience postulate ARMENIAN involves obsidian sources and trade in the ancient must be tested by analyzing the composition of the source. Near East. The chemical composition of some materials, such as chert in North America, varies greatly within a single source and different sources cannot be distinguished. Chert (and other M E D I T E R R A N E A N materials that do not comply with the provenience postulate) SEA therefore cannot be used for studies of place of origin. The principle, however, has been applied to a variety of archaeo- logical materials including obsidian, pottery, turquoise, tin, and many others. 15.8 Scientists can use the Terra Portable XRD Analyzer to achieve rapid results in the fi eld.

346 / PART 3 ANALYSIS AND INTERPRETATION CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 347 CERAMIC ANALYSIS METAL ANALY SIS

In addition to obsidian and other stones, a wide Archaeological metal artifacts and ores can also be variety of archaeological materials can be studied “sourced” using elemental analyses. For example, using elemental analyses, including ceramics, Heather Lechtman (born 1935) of the Mass- metals, bone, and many more. Ceramic analysis achusetts Institute of Technology, who won the often involves determining elemental concentra- prestigious MacArthur Fellowship (often called tions to examine the composition and potential the “Genius Grant”) for her work on prehis- sources of raw material for the pottery. Usually, toric metallurgy in South America, has used the NAA or ICP-MS is used for these analyses. Using elemental concentrations of di f erent ores to the chemical characterization of ceramic com- reconstruct the sources used for Andean bronze position, archaeologists can learn more about artifacts. In addition to identifying the sources manufacturing locations, trade and exchange, and mines used, Lechtman can also trace the and more general economic patterns. development of new metallurgical technologies. A simple example can provide an introduction More recently, scientists moved beyond ele- to ceramic analysis in archaeological chemistry. mental analysis of metal artifacts and ores to To evaluate the utility of elemental analyses for look more broadly at the environmental impact the study variation in ceramics, James Burton of mining in the past and present. For example, of the Laboratory for Archaeological Chemistry using ICP-MS and other methods to examine at the University of Wisconsin-Madison under- elemental concentrations, a group of scientists took an experiment using modern pottery from has identif ed shifts in pollution due to mining. three Mexican villages. Each village used dif er- Sediment samples from cores collected from three ent sources of clay for raw material and dif erent dif erent lakes in Peru and Bolivia showed lead recipes for their paste. Potsherds were obtained concentrations from pollution over the last 1,500 from each village and analysed by ICP-MS. A years. While we often think of environmental pol- plot of several elements in the pottery, combined lution as a modern problem, the scientists showed using a statistical technique known as discri- that smelting activities at dif erent mining centers minant analysis, produced results that almost released lead into the lake water. Lead pollution 15.11 exactly matched the three sets of pottery made was high after the Spanish arrived in the Andes in Plot of two discriminant functions (a statistical summary of several in the three dif erent villages (f g. 15.11); in this the Colonial period (f g. 15.12), and also in the different elements) that separate case, the archaeological chemistry data recorded Industrial age. Some lakes, however, showed lead the modern pottery from Mexico human behavior. Another ceramic provenience pollution as early as ad 400, which was related to into three distinct groups belonging to the three potters study can be found in Chapter 11 in the example intensive mining operations by the Wari, Tiwan- in different villages. involving the Salado polychromes. aku, and Inca empires. Unfortunately, pollution 15.12 archaeological studies) fractionate . T at means extensively to study human diets in the past and is not simply a modern problem. This Colonial-period watercolor that the proportion of dif erent isotopes present are described in the next section. Heavy isotopes of shows the silver mine at Potosi, Bolivia, which was one of the most can be changed by processes in nature involving strontium and lead, along with the light isotopes of important silver mines in the world heat, photosynthesis, enzymes, and the like. oxygen, have been used to look at human migra- ISOTOPIC ANALYSES until AD 1800. Heavier isotopes (with a mass greater than 40) tion and provenience. T is subject is discussed in do not fractionate to nearly the same extent as the following pages, along with an example from 4 Isotopes are atoms of the same element that lighter elements. Isotope analyses are normally the Maya site of Copan in Honduras. have dif erent atomic masses. (T ey are alternate reported in ratios of one isotope to another in states of the element with the same number of order to standardize the results for dif erent kinds protons, but a dif erent number of neutrons.) of materials and varying original isotope amounts. PREHISTORIC DIET AND ISOTOPES T ree isotopes of carbon, 12C, 13C, and 14C, have Isotopes of several elements are used in other IN ARCHAEOLOGY

0 already been encountered in Chapter 8, along applications in archaeology aside from the dating with isotopes of potassium (40K) and argon (40Ar). of archaeological materials. Lead isotopes have T e primary use of isotopes in archaeology, Radiocarbon dating relies on the ratio of 14C to been used to study the sources of silver, lead, and outside of dating, has been in research on past 12 Discriminant function 2 C to determine the age of archaeological mate- other ore deposits. Carbon isotopes have been diet. A basic principle of such studies is that rials. 14C is a radioactive isotope, unstable and used to determine the sources for marble and other “we are what we eat.” Carbon and nitrogen iso- subject to decay within a known period of time, stone composed of marine sediments (an example topes from the food we eat are deposited in our -4 meaning that the ratio of 14C to 12C will change of this testing is the Getty kouros statue, described skeleton. Human bone is a remarkable material, over time. T e majority of isotopes, however, at the beginning of this chapter). Carbon, hydro- composed of organic and mineral compounds are stable and not subject to radioactive decay. gen, and oxygen isotopes have been measured and water. Isotopic studies of the composition -8 -4 0 4 8 An important distinction is also made between in phytoliths to assess the environmental condi- of bone can utilize both the organic portion, Discriminant function 1 light and heavy isotopes. T e lighter elements tions when these plant silicates were formed. T e primarily the protein known as collagen, and (primarily carbon, nitrogen, and oxygen in isotopes of carbon and nitrogen have been used the inorganic or mineral portion of the bone.

348 / PART 3 ANALYSIS AND INTERPRETATION CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 349 15.14 species, such as corn, and temperate species, such White-tailed deer A schematic view of δ15N = +5.3‰ as wheat. Analysis of carbon isotopes from human carbon and nitrogen δ13C = -18.9‰ isotope ratios in bone from Mexico indicates that a dependence marine and terrestrial on corn began sometime before 4000 bc. systems. (Schoeninger Photosynthesis Nitrogen isotopes are used in much the same and Nelson, 1991.) Photosynthesis in corn and some in most plants Atmospheric carbon dioxide tropical plants way as carbon isotopes, but they provide dif- Tree leaves δ13C = -7 parts per thousand ferent information about diet. T e ratio of 15N δ15N = +3.0‰ δ13C = -26.0‰ (0.37 percent of all nitrogen in nature) to 14N Wheat Corn Walrus Human food (99.63 percent of all nitrogen in nature) is used δ15N = +13.3‰ 13 13 based on 50% of 13 δ C = -11.8‰ Average δ C = -26.5 Average δ C = -12.5 in paleodiet studies. T is nitrogen ratio is meas- parts per thousand each kind of plant parts per thousand ured in bone collagen using a mass spectrometer, Pilot whale δ15N = +16.7‰ usually at the same time as carbon isotope ratios. Wolf 13 δ C = -12.8‰ T is allows archaeologists to obtain two kinds of δ15N = +8.0‰ δ13C = -18.3‰ Human food Human food information to understand diet in the past from Mollusks chain based chain based a single sample of bone. δ15N = +12.5‰ on other on corn δ13C = -14.0‰ plants only Figure 15.14 provides a summary look at carbon and nitrogen isotope ratios in nature. C4 grass Kelp 15 15 δ N = +3.0‰ Small fi sh δ N = +7.0‰ Variations in nitrogen isotope ratios are largely 13 13 Rabbit δ C = -13.0‰ 15N = +10.0‰ δ C = -14.0‰ Plankton & Krill 15 δ 15 N = +5.0‰ 13 due to the role of leguminous plants in diet and δ δ C = -13.0‰ δ N = +7.0‰ 13C = ?‰ 13 the trophic level (position in the food chain) of δ δ C = -14.0‰ the organism. Atmospheric nitrogen is isotopi- Legume 15 cally lighter than plant tissues; values in soil tend δ N = +1.0‰ Blue whale 13 C grass δ C = -26.0‰ 3 15 to be even higher. Non-nitrogen-f xing plants, 15N = +3.0‰ δ N = +13.8‰ δ 13 13 C = -14.5‰ which derive nitrogen solely from soil nitrates, δ C = -26.0‰ δ can thus be expected to be isotopically heavier than nitrogen-f xing plants, which derive some nitrogen directly from the atmosphere. T ese values in plants are passed through the Bone collagen δ13C Bone collagen δ13C Bone collagen δ13C food chain accompanied by an approximately = -21.4 parts per = -14.4 parts per = -7.4 parts per ARCHAEOLOGICAL THINKING thousand thousand thousand 2–3‰ higher shift for each trophic level, includ- ing between mother and nursing infant. Grazing CLIMATE, ISOTOPES, AND VIKINGS IN GREENLAND animals exhibit 15N enrichment, and higher δ15N 15.13 T e amounts of dif erent isotopes of carbon values, compared to the plants they eat; predators Schematic representation of human 13 12 As we all learned in elementary school, Christopher Columbus Another group from Iceland went further north along the diet involving both maize, a tropical (reported as a ratio of C/ C) and nitrogen show enrichment relative to their prey species. grass with a higher δ13C value, and (ditto, 15N/14N) are measured in collagen using T ere are also dif erences in nitrogen isotope arrived in the Caribbean islands in 1492. But the fi rst Euro- west coast of Greenland and colonized the Western Settle- 13 wheat, with a lower δ C value. a mass spectrometer. While the level of these ele- ratios between marine and terrestrial sources peans to set foot in the Americas came almost fi ve hundred ment. These Viking groups took domesticated cereals and ments in bone is under strict metabolic control, of food that can be used in the study of past years earlier and were not Italian but Scandinavian: the Vikings. animals with them and successfully cultivated these crops the ratio of stable isotopes ref ects the ratio in the diets. Human consumers of terrestrial plants and Their daring voyages across the North Atlantic were made and fed their herds. The North Atlantic climate had entered diet. T ese isotope ratios are reported in parts animals typically have δ15N values of 6–10‰, in a series of shorter trips from Norway, Sweden, and Denmark a particularly good phase, known as the Medieval Warm per thousand (‰) and as a dif erence (delta or while consumers of freshwater or marine f sh, to Great Britain and Ireland, and then to the Faeroe Islands, Period, around AD 900. Temperatures were 1 to 2 degrees δ) between the measured ratio in the sample seals and sea lions usually have δ15N values of Iceland, Greenland, and eventually to Newfoundland in eastern Celsius warmer than today on average and the growing and a known standard. Convention dictates that 15–20‰. Nitrogen isotope ratios may also vary Canada (fi g. 15.15, p. 352). The Vikings conquered parts of season was longer. The Viking population of Greenland soon carbon is reported as δ13C and nitrogen as δ15N. with rainfall, altitude and other factors. Britain and Ireland by AD 800 and occupied many of the island expanded to between 4,000 and 5,000 people. After AD 1300, T ere are two primary sources of variation in T e composition of past human diet is one groups in the northern British Isles, including the Shetlands, however, those numbers began to decline, and by about 13C in human diet and bone collagen: dif erent of the most important questions in prehistoric Orkneys, and Hebrides. As explorers and colonists, they were AD 1450 Greenland was completely abandoned by the Norse. ratios in the kinds of plants we eat and dif erent research. T e quest for food directly af ects many the fi rst people to settle on the Faeroe Islands and Iceland The present icecap on Greenland is more than 2 kilo- ratios between terrestrial and marine foods. In aspects of human behavior and society, includ- in AD 874. On Greenland and in North America, the Inuit and meters (1.25 miles) thick, made up of layer upon layer of ice certain kinds of tropical plants, such as corn, 13C ing group size and social organization, residence American Indians had been present for thousands of years. and frozen snow in a stratigraphy of the last several hundred is more abundant because of the ways that the patterns, technology, and transportation. T e The story of the Viking exploration of the North Atlantic is thousand years. Ice cores from this deep ice sheet provide plants produce carbon during photosynthesis. use of carbon and nitrogen isotopes in tandem an incredible saga of many tales. One chapter concerns the information on past climate on Greenland and show a steady People who eat these kinds of tropical grasses provides a powerful means for determining the colonies on Greenland and tells of their initial success and decline in maximum temperature during the fi ve hundred therefore have higher amounts of 13C isotopes sources of food in the human past. An example subsequent failure in the light of major climatic change. A years of the Viking occupation. This cold period between in their bones. Changes in this isotope ratio in of the application of isotopes to human diet group of Icelandic farmers led by Erik the Red founded the AD 1300 and 1850 is called the Little Ice Age, and its effects prehistoric bone can indicate when corn became is provided in the next section on the Vikings Eastern Settlement in southwest Greenland around AD 985. were dramatic in the North Atlantic. an important part of the diet.Figure 15.13 shows in Greenland. the results of a diet involving both a tropical

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15.15 Changes in climate played a major role in Viking history. growing season declined, the Viking way of life collapsed. At The homelands, settlements, and routes of the Vikings in the The Medieval Warm Period provided better growing conditions the same time, colder conditions on Greenland increased the North Atlantic (adapted from in Scandinavia and supported more people, which may have herds of seal and reindeer, which meant that the Inuit hunters McGovern and Pedarkis, 2000). forced the exploration and colonization of new land. Several further north on Greenland fl ourished. BAFFIN GREENLAND Arctic Circle hundred years later, as the Little Ice Age took hold and the ISLAND SHETLAND Isotopic studies of the ISLANDS tooth enamel from Norse c. 870 burials in Greenland doc- ICELAND . 800 ument these changes in c. 860 c climate. Oxygen isotopes— ORKNEY ISLANDS ANCIENT MIGRATION AND ISOTOPES moved. T e application of isotopic tracers, a refl ection of atmospheric Labrador Current IN ARCHAEOLOGY however, has made it possible to identify human temperature—in tooth migration in the people themselves. T e prin- enamel show a clear One of the core questions in archaeology con- ciple is straightforward. Tooth enamel forms increase in cold during cerns changes in material culture. New things during infancy and does not change during ATLANTIC OCEAN the period of settlement are innovations and they represent what is called life. Bone, on the other hand, is constantly LABRADOR (fi g. 15.16). Carbon iso- culture change; for example, a new kind of rebuilding itself as part of the body’s mainte- topes, on the other hand, L’Anse aux Meadows projectile point appears, domestic plants and nance plan, as anyone who has broken a bone indicate a marked increase animals are found for the f rst time at a site, or knows. T e composition of tooth enamel then in the proportion of marine Viking homelands a new burial practice spreads across a region. is composed of the things an individual (and his foods in the diet over time, Viking settlement areas T e question then arises; from where did these or her mother) ate during infancy.T e composi- from approximately 20 15.17 new things come? Did new people coming to tion of bone is a product of the foods consumed percent when the Vikings Kelly J. Knudson taking a sample of dental enamel from a prehistoric the area introduce culture change, or did local during the last years of life. arrived to approximately 80 percent at the end of their time on the ice. If the crop failed, the cattle and sheep died before tooth using a dental drill. people independently invent these things or Certain isotopes in the foods we eat are geo- on Greenland. Based on the isotopic data, as temperatures the seals arrived and the Norse would starve. simply borrow foreign ideas and artifacts? T is graphically distinctive. Isotopes of strontium declined and the growing season shortened, the Viking inhab- Archaeological evidence corroborates this scenario. Excava- is a question of invention versus dif usion, and and oxygen are particularly good signatures for itants of Greenland ate more seals and fi sh. A long summer tions at Norse houses from the later period of the settlement is one of the more problematic questions for the place of residence. Strontium isotopes vary was necessary to grow hay to store and feed their cows and have revealed the skeletons of cattle that died in their stalls archaeologists to answer. among dif erent types of rock and go into the sheep through the spring, when the Norse could hunt seals during the winter. Other bioarchaeological information sug- T e dif cult part is determining if people body through the food chain, from rock to soil gests a clear decline in human nutrition. moved around in the past. We can usually to plant to animal to human. Oxygen isotopes There are indications of a decline in Years AD identify exotic artifacts, but cannot determine enter the body in drinking water, which ulti- 600 800 1000 1200 1400 1600 1800 2000 stature in the Greenland Vikings over how the artifacts came to be in that place. mately comes from rainfall. Isotopes in rainfall time and a number of the later skeletons For example, iron and horses were absent in vary with temperature and latitude. Rain that -12.0 exhibit bioarchaeological evidence of 100 North America until the Europeans arrived. falls in warm areas close to the sea has a high disease and malnutrition. But, after the arrival of Europeans in eastern oxygen isotope ratio, while rain that falls more -14.0 80 North America, iron hatchets and domesticated inland and at higher elevations and latitudes horses quickly spread across western North has a lower ratio. 60 -16.0 America, where they were found long before T ese isotopes can be measured in the enamel 15.16 the Europeans who introduced them reached (f g. 15.17) and bone of a human skeleton 40 Climatic changes over the last fourteen that part of the continent. T e answers to this using a mass spectrometer. T e isotope ratios in -18.0 hundred years, revealed in Greenland ice Carbon isotope ratio Carbon isotope 20 cores, document periods of warmer and conundrum are in fact known—axes were tooth enamel come from the place of birth; the

Marine food diet (percentage) Marine food colder conditions than today. The temperature popular trade items among Native American isotope ratios in bone come from the place of -20.0 curve on the bottom of the diagram is based 0 on oxygen isotopes, a proxy for atmospheric groups; the horses came from the earlier Spanish death. If the ratios in the enamel and the bone temperature. The Medieval Warm Period colonists in the Southwest—but the example of the same individual are dif erent, that person Settlement witnessed the expansion of the Vikings declines illustrates the complexity of tracing the origins must have changed their place of residence, i.e. Warmer across the North Atlantic while the Little Ice Cooler Age documents a time of cooler conditions of cultural change. Artifacts and other objects she or he must have moved. In some cases, it and declining harvests. The carbon isotope Norse arrive Norse disappear are often used as markers of groups of people is possible to determine not just that a person evidence from human tooth enamel shows a in archaeology, but such objects can be traded, moved, but also to suggest from where they Medieval Warm Period Little Ice Age shift from terrestrial to marine diet during this period. (Data from Dansgaard et al. [1975] and borrowed, or stolen, and are not necessarily may have come. Arneborg et al. [1999].) carried directly by the people who made them. Until recently, archaeologists have not been able to determine directly if people themselves

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IN FOCUS THE FIRST KING OF COPAN, A CLASSIC MAYA CENTER IN HONDURAS

One example of identifying human migration from isotopes fi rst king of Copan. He was apparently quite a warrior, having This individual in the central tomb was an older male, individual, the wounds he had suffered, and the probable in the skeleton comes from the Maya area in Mesoamerica. won a number of major battles. He was said to have come to between fi fty and sixty years of age, and his skeleton showed place of birth correspond with what we know of Yax Kuk The site of Copan [CO-pahn] is located in Honduras, in the Copan from the north in AD 427 to found the dynasty at what a number of old breaks and lesions that were probably M’o. This is likely his tomb and skeleton at the base of the southwestern corner of the Maya region. The central part of this was then a simple village. Was this deep tomb at the base of the result of confl ict and warfare. Certainly the age of the Copan acropolis. huge site is dominated by an acropolis covered with temples, the Copan acropolis the grave of Yax Kuk M’o? This fi rst king buildings, and inscribed stone stelae and altars (fi g. 15.18). was also sometimes depicted wearing a costume typical of the This was the civic and ceremonial focus of the site, and the major Mexican center of Teotihuacán, almost 1,200 kilometers residence and burial place of its rulers. (745 miles) to the northwest near modern-day Mexico City. In the 1990s, Robert Sharer (1940–2012) from the University Did he come from that distant center? of Pennsylvania and a team of archaeologists began to tunnel Isotopic analysis was used to answer these questions. into the artifi cial hill of the acropolis to see what lay inside. Bones and teeth from the individual buried in the central tomb This large terraced mound had been built in stages, each new and several of the adjacent graves were analysed. This infor- level burying the previous architecture under layers of clay mation was compared with isotope ratios from modern-day and gravel. The tunnel of the archaeologists revealed earlier local animals and human bone from other parts of the Maya temples and altars that had been left intact and were preserved region. The combination of strontium and oxygen isotopes almost perfectly with their brightly painted facades. At the in the tooth enamel from the central tomb burial points to a bottom of the earliest level of the acropolis they uncovered place of birth to the north, perhaps somewhere around the a series of graves and human burials around a large central site of Tikal, in modern-day Guatemala, meaning that this tomb (fi g. 15.19). It seems that the mound was initially built individual most defi nitely did not come from Teotihuacán. The to mark the burial place of one of the early rulers, but which regalia he wore only emphasized symbolic connections with one? There were sixteen kings listed in the dynasty at Copan. that important center. Ancient Maya hieroglyphic inscriptions abound at Copan and often refer to the important events in the lives of these rulers,

such as birth, marriage, conquests, and death. A number of 15.18 inscriptions described Yax Kuk M’o [YASCH kook moe], the A computer reconstruction of the acropolis at Copan, Honduras.

15.19 The primary burial under the acropolis at Copan, Honduras, probably the tomb of Yax Kuk M’o.

ORGANIC RESIDUES IN ARCHAEOLOGY

T e food and many raw materials that humans and on artifacts and sediments that can survive use are organic—meat, f sh, fowl, vegetables, for thousands of years. fruits, wood, hide, bone, antler, thatch, fur, and Trace organic compounds are distinguished more—and come from living things.T ese mate- from visible organic residues, such as charred rials were once abundant at the living places food on pottery or other macroscopic organic of prehistoric people. Unfortunately, in most remains. Analysis of trace organic compounds cases this “biological” component of the past is (which have adhered to or been absorbed into very susceptible to decomposition and does not the structural matrix of archaeological materi- survive to the present. Fortunately, however, als) can provide information about past artifact biological materials sometimes leave traces in function, diet, and other aspects of prehistoric

354 / PART 3 ANALYSIS AND INTERPRETATION CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 355 societies. This branch of archaeometry is either through contamination—the addition of sometimes referred to as molecular or biomo- new materials to the matrix—or the breakdown IN FOCUS lecular archaeology. of the original molecules into small, unidentif - A variety of archaeological materials may able components. T ere are in fact a relatively ZOOLOGY BY MASS SPECTROMETRY contain trace organic compounds, including small number of both reliable and useful studies ceramics, stone tools, grinding stones, cooking that have been conducted to date. slabs, plaster, fecal material, soil, and sediments. Most of the ef ort, and success, in the organic Zoology by Mass Spectrometry (ZooMS) is a new technique signature for many species. In this way the identity of the T e best preservation seems to be in such arti- analysis of archaeological residues has been in for identifying species of animal from otherwise unidentifi able animal becomes available. facts as pottery in which the structural matrix characterizing specif c organic molecules retained bone fragments in archaeozoology. A small extract of collagen There are many uses for this new method. Zooarchaeolo- of the material has absorbed trace organic com- in potsherds. Highly specif c residues from fruits, protein is taken from the bone, usually without damage to the gists are normally unable to distinguish sheep and goats pounds, thus preventing, or at least reducing, the milk, wine, olive oil, and cedar wood oil have specimen. That protein is digested into peptides, a compound because of the similarity of their skeletons. These two introduction of contaminants from handling or been identif ed in various studies. Other poten- of two or more amino acids in a chain. These peptides are species, however, can be distinguished by ZooMS primarily diagenesis (physical and chemical changes after tially diagnostic compounds recovered from placed in a mass spectrometer and the isotopic signature is through a single peptide showing a mass difference. deposition or burial), and the oxygen-induced potsherds include proteins, some of which are recorded and compared to a reference library with the known degradation that can interfere with the identif ca- diagnostic of certain animal foods. No doubt as tion of the original parent material. scientif c instrumentation becomes more sensitive Although the analysis of trace organic com- to the identif cation of ancient compounds, and pounds has great potential in archaeological as these instruments become more accessible to research, a number of problems remain, largely archaeology, studies of trace organic compounds CONCLUSIONS due to post-depositional changes in the molecules will become more common. Archaeological chemistry uses the elemental and has grown steadily to more than twenty-f ve, and isotopic characterization of archaeological mate- there are an increasing number of archaeologi- rials and organic analyses to learn more about cal science laboratories and undergraduate and the past. Studies using archaeological chemistry graduate degree programs all over the world. IN FOCUS can identify unknown materials, authenticate Along with this expansion have come new and TRACES OF CHOCOLATE IN CERAMIC VESSELS the antiquity of pieces of questionable origin, exciting developments that are revolutionizing FROM THE NORTH AMERICAN SOUTHWEST and characterize the chemical composition of the way archaeology is conducted. Archaeologi- various raw materials and f nished artifacts. A cal chemistry, and archaeometry more generally, large part of archaeometric research has to do is a particularly exciting branch of archaeology Archaeological sites in the Chaco Canyon region of New Mexico with determining provenience, or place of origin, because there are so many things to be learned frequently provide evidence of many different exotic goods that to investigate questions of exchange or move- and new approaches are coming so quickly. were imported from Mesoamerica, such as copper bells and ment in the past. Archaeological chemistry is also a fascinating area scarlet macaws. The archaeologist Patricia Crown (born 1953) Archaeological chemistry involves many more of archaeology because it intriguingly combines wondered if other exotic goods were also being transported methods and materials than are discussed here. the sciences and humanities, the quantitative and thousands of kilometers from Mesoamerica, and focused her In this chapter, we have presented some informa- qualitative, and the objective and subjective in attention on ceramics. Certain ceramic vessels were decorated tion about the goals of archaeological chemistry, solving problems concerning our human past. in a Puebloan black-and-white style typical of Chaco Canyon, about instrumentation, and about laboratories. yet the cylinder shape was unusual (fi g. 15.20). The shape of We have focused on the major techniques of ele- the ceramic vessels resembled Mesoamerican cylinder jars mental and isotopic analyses and archaeological that were used for a chocolate drink made with cacao beans, chemistry. Examples have included the elemental the key ingredient in chocolate. A team of scientists used characterization of obsidian for information GC-MS and other techniques to see if the organic residues on source and exchange, and isotopic studies in the ceramic vessels contained theobromine, which is a of prehistoric Greenland that revealed changes chemical found in large quantities only in the cacao plant. in diet associated with climatic deterioration. Many of the vessels did indeed contain theobromine, showing Isotopic investigation of human mobility in the that ancient peoples in the Southwest United States imported Maya region documents the origin of the f rst and consumed cacao that had been grown thousands of kilo- king of Copan to the north, probably in the meters away in the jungles of Central America. Peten [PAY-ten] region of Guatemala. Archaeological chemistry has expanded dra- matically in the last three decades. One way to consider this is to look at the meetings and pub- lications that appear each year in this f eld. T e 15.20 Ceramic vessels from Chaco Canyon, New Mexico that were number of symposia that discuss archaeological used as containers for a chocolate drink. science at the annual meetings of American archaeologists increases year-on-year, the number of journals focused on archaeological science also

356 / PART 3 ANALYSIS AND INTERPRETATION CHAPTER 15 ARCHAEOLOGICAL CHEMISTRY / 357 ARCHAEOLOGY PROJECT ARCHAEOLOGY PROJECT (CONTINUED) ISOTOPES AND PREHISTORIC DIET

can use different shapes or colors for the dots for males and information on the site of Huaca Blanca, write a brief essay Now it is your turn. You are an archaeologist specializing in the dots for females. about diet at the site. Please answer each of the questions archaeological chemistry, and you are investigating what Table 15.1 Measurements of bone-collagen isotope ratios What does this scatterplot of isotope data tell you? Do you below in a brief paragraph. for carbon and nitrogen and the carbon:nitrogen ratio people ate at the ancient Peruvian site of Huaca Blanca. The see distinct clusters or groups of data points? If so, what do 1. What, if any, evidence did you fi nd for diagenesis, or for for twenty-four samples of bone from the archaeological site was on the coast, so the site’s inhabitants could have had site of Huaca Blanca. In the table, M=male, F=female, these mean? Based on your readings, you know that eating contamination in the bone samples? Describe how you access to fi sh and seafood from the Pacifi c Ocean, but Huaca and PM=possible male, based on the skeletal sex of the seafood and fi sh from the Pacifi c Ocean would lead to higher decided that the bone samples were well preserved or not. Blanca was also surrounded by agricultural fi elds that could individuals, who were all adults when they died. nitrogen isotope values, and that eating corn from the neigh- 2. Did you fi nd any clusters or groups in your scatterplot? How have been used to grow corn, beans, and cotton. After receiv- boring agricultural fi elds would lead to higher carbon isotope did you interpret the scatterplot of your data? ing permission from the Peruvian government to export the Sample Number Sex C:N δ13C δ15N values. What did people who were buried at Huaca Blanca eat? 3. What did the people buried at Huaca Blanca eat? Did you samples and analyse them in your laboratory, you prepared the Did females and males have different diets? fi nd one or more groups in the dataset, based on diet and/ 1 F 3.2 -14.9 15.6 archaeological human bone samples and analysed the stable Given your analysis of the isotope data and thearchaeological or sex? How did you interpret these groups? carbon and stable nitrogen ratios in the collagen extracted 2 M 3.2 -14.6 4.9 from the bone samples using a mass. Now, after months of preparing and analysing the samples, it is time to interpret 3 F 3.6 -16.8 14.7 Table 15.1 your data, which are shown in . 4 F 3.4 -10.2 15.7 First, you need to decide if the samples were well pre- STUDY QUESTIONS served, or if they were contaminated by groundwater or the 5 F 3.2 -17.9 18.0 burial environment (diagenesis). When you excavated the bone 6 F 3.5 -12.0 14.3 1. What kinds of materials are studied in 4. Discuss three isotope ratios and samples, you noted that they resembled fresh, healthy bone, archaeological chemistry laboratories? how they are used in archaeological rather than fossilized bone. The carbon:nitrogen (C:N) ratio of 7 PM 3.8 -17.4 13.4 chemistry. pure, fresh collagen is 3.2. A carbon:nitrogen value between 2. Elemental analysis is one of the 2.9 and 3.6 is considered necessary for a sample to be reliable. 8 F 2.9 -17.8 12.7 primary methods of archaeometric 5. Organic residues are a potentially Now it is time to analyse the carbon and nitrogen isotopic research. What methods are available important but diffi cult to analyse 9 F 3.1 -23.0 16.0 data. One way to do this is to make a scatterplot so you can to measure elemental composition in source of information about the compare two variables at the same time (the carbon isotope 10 F 2.8 -17.6 15.5 archaeological samples? past. Discuss these materials and 13 15 techniques for analysis. data, or δ C, and the nitrogen isotope data, or δ N). To make 3. How do archaeologists and 11 M 3.2 -22.8 6.3 a scatterplot, draw two lines on the graph paper, one hori- archaeological chemists learn about zontal and one vertical. The vertical line should rise from the 12 M 3.3 -17.0 6.5 past human diets? left end of the horizontal line. The horizontal line will be the carbon isotope values. Mark the left end of the line with the 13 F 3.2 -19.0 14.7 minimum value in the dataset and the right end of the line with the maximum value. You will need to indicate some of the 14 M 3.2 -15.6 5.6 FURTHER READING values for the grid lines between the minimum and maximum 15 M 3.1 -16.5 4.3 values to make it easier to plot the bone samples. Now do the D. R . Brothwell and A. M. Pollard (eds.), Archaeology (Cambridge: Cambridge University Handbook of Archaeological Sciences Press, 2007). same thing for the nitrogen isotope values along the vertical 16 M 3.0 -14.9 7.4 (Chichester, England: Wiley, 2001). line. Minimum value at the bottom; maximum value at the top. A. Mark Pollard and Carl Heron, Archaeological Put values on some of the grid lines in between. 17 F 3.2 -19.7 16.2 M. Buckley, M. J. Collins, J. Thomas-Oates, Chemistry, 2nd edn (Cambridge: Royal Society Now you are ready to make a scatterplot. Look at the fi rst 18 F 3.4 -19.8 7.4 and J. C. Wilson, “Species identifi cation by of Chemistry, 2008). sample; read the value for the carbon isotope value (δ13C) and analysis of bone collagen using matrix-assisted T. Douglas Price and James H. Burton, An fi nd this point on your horizontal line. Now read the value for 19 F 3.2 -18.9 8.3 laser desorption/ionisation time-of-fl ight mass Introduction to Archaeological Chemistry (New the nitrogen isotope value ( 15N) for the same sample. Find this spectrometry,” Rapid Communications in Mass δ York: Springer, 2011). point on your vertical line. Now draw an imaginary horizontal 20 M 3.2 -8.9 4.3 Spectrometry 23 (2009): 3,843–54. line from your nitrogen isotope value and an imaginary vertical J. Thomas-Oates and M. J. Collins, 21 M 3.2 -22.7 5.2 Julian Henderson, The Science and Archaeology “Distinguishing between archaeological sheep line from your carbon isotope value. Mark a dot or small circle of Materials: An Investigation of Inorganic and goat bones using a single collagen peptide,” at the point where those two imaginary lines cross. Now you 22 M 3.3 -22.9 5.7 Materials (London: Routledge, 2000). have reduced two numerical values to a single point on the Journal of Archaeological Science 37 (2010): graph. Continue this process for the rest of the bone samples. 23 M 3.2 -21.4 4.0 Joseph B. Lambert, Traces of the Past: Unraveling 13–20. the Secrets of Archaeology through Chemistry You should end up with one dot on the graph for each sample. 24 F 3.4 -21.4 6.6 N. L. Van Doorn, “ by Mass (New York: Addison Wesley Longman, 1997). If you want to add another variable to your scatterplot, you Spectrometry (ZooMS),” Encyclopedia of Global A. Mark Pollard, Catherine Batt, Ben Stern, and Archaeology (New York: Springer, 2014), Suzanne M. M. Young, Analytical Chemistry in pp. 7,998–8,000.

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