Dating Methods In Archaeology Research Paper

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1. Introduction: Estimating Age In The Archaeological Record

Of the twenty or so dating methods employed in twenty-first-century archaeology, the US Congressional Office of Technology Assessment (OTA) report on Technologies for Prehistoric and Historic Preservation (US Congress, OTA 1986) listed only seven and highlighted two radiocarbon and archaeomagnetic techniques; see Taylor 2000, pp. 75–60. In many regions of the world, radiocarbon, dendrochronology, obsidian hydration, and archaeomagnetism are the most common physical dating methods used, presumably in that order, but often together as a group providing redundant checks on one of the most important goals of archaeology—providing a framework of time, a chronology, upon which a rational reconstruction of the past can be built. Regardless of an archaeologist’s theoretical or political perspectives, the first goal is to order regional prehistoric or historic sites, a single site, or a portion of the site into meaningful cultural and chronological segments. Chronology is a primary goal, but should not be confused with the intent of reconstructing the past, regardless of what an archaeologist’s definition of the ultimate purpose may be.

During the formative cultural historic perspective in archaeology in the first half of the twentieth century, constructing regional and site-oriented chronologies became the primary goal of archaeology, particularly in North America and the UK (Trigger 1989). A dissatisfaction with this rather unilineal explanation of the past stirred archaeologists to look beyond simply constructing chronologies and to begin to understand process and social relationships in the past. Dating methods and the construction of cultural chronologies, however, have remained the basement upon which archaeologists build their understanding of social process through time.

While it would be optimal to discuss all the potential dating methods available to archaeologists, this is not possible in a short synopsis. The most commonly used methods, and those showing promise, will be covered here (see Table 1 and Fig. 1). Refer to the publications in the Bibliography: for more detailed treatments.

2. Archaeological Stratigraphy

Stratigraphic relations have always been the primary method to infer the relative age of artifacts within a site. Stratigraphy is defined here as the study of the spatial and temporal relationships between the sediments and the soil (Waters 1992, pp. 60–1). Much of this section’s discussion can be more robustly understood by referring to the entry Geoarchaeology; an awareness of the geological processes of archaeological site formation is crucial to an understanding of dating archeological sediments. Indeed, the methods used by Quaternary geologists to date sediments include most of the methods used by archaeologists and discussed here (see Fig. 1). Stratigraphic studies of archaeological sites are designed to define objectively and categorize the sediments and soils, the contact units between them, and the amount of time they represent, as well as their relationship to the surrounding sediment history.

Archaeological stratigraphy is based on the geological concepts of the law of superposition, which states that older sediments are emplaced at a lower level than more recent sediments. Therefore, sites, features, and artifacts residing in lower levels are, by definition, older than those in upper levels. This conceptual framework in archaeology appears to have begun with John Frere in 1797 attempting to understand the relationship between stone axes in a sedimentary sequence in England: ‘The manner in which…[the hand axes] lie would lead to the persuasion that it was a place of their manufacture and not of their accidental deposit…It may be suggested that the different strata were formed by inundations happening at distant periods’ (Frere in Rapp and Hill 1998, p. 5).

This idea that features or artifacts found within a site in the same stratigraphic level are contemporaneous forms the foundation upon which archaeological stratigraphy is based. In early twenty-first century archaeology, the various relative and absolute dating methods such as radiocarbon or archaeomagnetic dating are used to verify this assumption and produce a site chronology (see Fig. 2). Fig. 2 shows a simple stratigraphic profile of a single excavation unit with the relative positions of natural and cultural features, and the position of radiocarbon dates recovered from the various levels. Note that the radiocarbon dates indicate that, in general, the stratigraphy is intact in that the oldest dates are at the bottom and the latest dates at the top, except for one date (CAMS 43177) at 3690 50 BP which seems to be out of sequence and suggests ‘small-scale’ disturbance probably caused by the digging of the pit structure during the later ceramic period (Shackley et al. 2000).

Time-sensitive artifacts, such as previously dated pottery or projectile point types, can be used as index fossils within the stratigraphic column to create a relative chronology within the site. The stratigraphic example discussed above also used index fossils, in this case projectile point types, to add another chronological piece of information. In Level 8, where the early radiocarbon date as well as some more recent radiocarbon dates were recovered, Middle Archaic as well as Late Archaic projectile point forms were recovered; both confirming the time range suggested by the radiocarbon date ranges (Fig. 2, Shackley et al. 2000). In this instance the stratigraphy, radiocarbon dates, and index fossils all contributed to an understanding of the site chronology and the integrity of the archaeological deposit.

2.1 Constructing Stratigraphic Chronologies: Competing Ideas

It is important to note, however, that there is considerable recent controversy over the proper method to employ in the interpretation of archaeological stratigraphy (Farrand 1984, Harris et al. 1993, Stein 1987, Waters 1992). Archaeological stratigraphic codes similar to geological stratigraphic codes and methodologies have been proposed but not generally adopted, since many geoarchaeologists are convinced that the existing geological code is adequate for archaeological research (see Stein 1987). More recently, Harris has proposed an ‘archaeological tool’ to understand archaeological stratigraphy called the ‘Harris Matrix,’ essentially a simple postexcavation way in which to understand the relationships between stratigraphic units in a single diagram as reflected on paper, or more recently in digital form (see Harris et al. 1993). Farrand (1984) and others, mainly geologists, have questioned Harris’s assumption that archaeological stratigraphy is primarily culturally conditioned rather than geologically determined. In a Harris Matrix analysis the relationship between stratigraphic units is based mainly on index fossils, for example the relationship between artifacts and features, rather than geological features or context— essentially emphasizing content rather than structure. Despite criticism from many geoarchaeologists, the Harris Matrix analysis has become increasingly popular with archaeologists working in varieties of geological and cultural contexts worldwide, particularly in Europe. The growing popularity of the Harris Matrix approach will probably continue, particularly in small site settings where a larger geological view is difficult to obtain or not necessarily relevant.

3. Sidereal Dating Methods

Sidereal dating methods include historical records, glacial varve dating, and dendrochronology. While only dendrochronology will be discussed here, glacial varve dating is quite useful in the upper latitudes, and in some cases may be quite precise. Historical records are a basic dating tool in historic and ethnohistoric archaeology, in addition to the social information they may contain.

3.1 Dendrochronology

The science that uses annual tree rings for dating past events and reconstructing past environmental conditions has undergone explosive growth in recent decades (Dean 1997). While dendrochronology as an archaeological dating tool enjoyed tremendous expansion in the 1990s, particularly in western North America, Europe, Siberia, and the eastern Mediterranean, it is used wherever appropriate trees occur and a sequence has been established. Most importantly, directly dated tree rings have been instrumental in the calibration of the radiocarbon timescale discussed below. This process indicated that the radiocarbon chronology underestimates the true ages of materials older than 2,000 years and that ¹⁴ C dates must be corrected.

The technique is based on the concept that each year (four seasons) a tree will accumulate one growth ring, and that that ring’s attributes reflect the specific climatic regime of that year. Since each year is essentially a unique climatic record, the attributes of the tree ring (thickness of inner and outer bands) are correspondingly unique. In trees, particularly fast- growing conifers, the progression of rings from pith to circumference presents an ‘unalterable temporal order, and the production of but one ring per year provides the incremental regularity necessary to establish a fixed [and absolute] time scale’ (Dean 1997, p. 34). More than 180 tree and shrub species worldwide possess the attributes required for successful dendro-chronological studies: visible and unambiguous ring definition, production of a set number of rings (generally only one) per year, mainly climate-con- trolled growth, and the presence of useable morphological features that allow for ring comparison. Cross-dating, matching patterns of ring variation among trees, is the necessary principle of dendrochronology. A sequence within a region is derived from overlap between cut trees as well as archaeological specimens, sometimes with great time depth into the thousands of years. While this process is apparently simple, the application necessarily requires precision. At the turn of the twenty-first century, image analysis technology was being used to develop electronic workstations, including image databases in laptop computers, perform routine comparisons between the database and archaeological wood samples similar to techniques used in obsidian hydration analysis.

Today, in a number of regions of the world (upper altitudes in the North American Southwest, Western Europe, the Eastern Mediterranean) dendrochronology forms the backbone of chronometric dating. When available, dendrochronology provides an absolute chronology that anchors other dating techniques.

4. Isotopic Dating Methods

Perhaps the one area of dating that has seen the greatest advances recently are techniques based on radioactive decay: ¹⁴C, K-Ar, and ⁴⁰Ar / ³⁹Ar. Advances in accelerator mass spectrometry and laser fusion have propelled these techniques into the forefront of the arsenal of methods used to deal with time in the archaeological record. Importantly, ¹⁴C is g enerally restricted to dating the last 50,000 years and ⁴⁰Ar/³⁹Ar , previously restricted to time periods near and over one million years, are now nearly overlapping with ⁴⁰Ar/³⁹Ar using the laser fusion method and yielding younger and younger ages. These methods do have limitations, but the organic and mineral restrictions are being transcended almost daily.

4.1 Radiocarbon Dating ( ¹⁸C)

Given that the greatest level of human activity occurred after the evolution of modern Homo sapiens, in the last 45,000 years or so, radiocarbon dating has become the most commonly relied upon dating method in archaeology (Taylor in Taylor and Aitken 1997). Radiocarbon dating, now in its fifth decade of general use, is a primary tool used by archaeologists and Quaternary geologists to date the past.

4.1.1 The Radiocarbon Method. There are three p r in-cipal isotopes of carbon which occur naturally: ¹²C, ¹³C (both stable), and ¹⁴C (unstable or radioactive). The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 ( ¹⁴C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14. The reaction is: ¹⁴N+n→¹⁴C+p (where n is a neutron and p is a proton).

The ¹⁴C formed is rapidly oxidized to ¹⁴CO₂ and enters the Earth’s plant and animal life-ways through photosynthesis and the food chain. Plants and animals which utilize carbon in biological food chains take up ¹⁴C during their lifetimes. They exist in equilibrium with the ¹⁴C con centration of the atmosphere; that is, the number of ¹⁴C atoms and nonradioactive carbon atoms stays approximately the same over time. As soon as a plant or animal dies, they cease the metabolic function of carbon uptake; there is no replenishment of radioactive carbon, only decay.

Libby, Anderson, and Arnold (Taylor and Aitken 1997) first discovered that this decay occurs at a constant rate. They found that after 5,568 years half the ¹⁴C in the original sample will have decayed, and that after another 5,568 years half of that remaining material will have decayed, and so on. The half-life (t₁/₂) is the name given to this value, which Libby measured at 5568±30 years. This became known as the Libby half-life. After 10 half-lives, there is a very small amount of radioactive carbon present in a sample. At about 50,000 to 60,000 years, then, the limit of the technique is reached (beyond this time, other radiometric techniques must be used for dating, such as ⁴⁰Ar/³⁹Ar, as discussed above). By measuring the ¹⁴C concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the number of decay events per gram of carbon. By comparing this with modern levels of activity (1890 wood corrected for decay to AD 1950) and using the measured half-life, it becomes possible to calculate a date for the death of the sample.

It follows from this that any material which is composed of carbon may be dated. Herein lies the true advantage of the radiocarbon method—it is able to be uniformly applied throughout the world. A list of the tremendous quantity of organic material that can be dated by radiocarbon is available at the University of Waikato’s radiocarbon Web site, a standard for understanding the technique: http: //c14.sci.waikato.ac.nz/webinfo/int.html.

4.1.2 Calibration And Radiocarbon Dating. As mentioned above, there are a number of effects that can cause errors in the measurement of radiocarbon dates. For example, shell, in constant contact with more recent atmospheric carbon, will generally yield young dates; conversely a shell artifact deposited in older limestone sediments will obtain a much older date than its actual death. These reservoir effects are in part mitigated by the use of various calibration algorithms, such as the CALIB (2001) and OxCal (2001) programs, both available on-line.

When a radiocarbon lab returns a date from a sample such as 5568 BP, it does not mean that it dates to 3619 BC, because the true half-life of radiocarbon is 5730 years, and, more importantly, the proportion of radiocarbon in the atmosphere has varied through time, as discussed above. So the calibration utilities are written to allow for differential in the absorption of ¹⁴C by different materials (i.e., marine shell versus wood charcoal), and to allow for different atmospheric effects. Using the CALIB 4.2 calibration, a radio- carbon assay of 5568 BP with a 1 standard deviation of 55 years on wood charcoal yields a date of:

Note that there are two dates with ranges of a number of years. The range includes the one standard deviation, and the two dates are due to multiple intercepts on the calibration curve. We can be 68.3 percent certain that the dates fall either from 4454 to 4416 BC or from 4408 to 4354 BC. There are multiple possible dates because the radiocarbon date of 5568 BP intercepts the calibration curve at more than one point. Due to the perturbations in the absorption of radiocarbon over the millennia, the variance is sometimes full of ‘wiggles’ on the curve, so placement can occur at two or more points.

Radiocarbon dates are reported in a standardized method, as shown in Table 2. The convention calls for reporting the provenience of the sample, the laboratory number, the radiocarbon age, and then the calibrated (in this case dendrocalibrated) age at one or two standard deviations (note that most of these dates yielded multiple intercepts). The calibration method used and any further contextual information should also be supplied.

4.1.3 Accelerator Mass Spectrometry (AMS) And Radiocarbon. From the inception of radiocarbon dating, ¹⁴C ages of samples were calculated by decay counting in mainly scintillation counters. This requires a relatively large sample, depending on the amount of carbon remaining in that sample. By the late 1970s a number of researchers discovered that when accelerating sample atoms in the form of ions to much higher energies in particle accelerators, a much smaller sample was required to derive confident dates—in most cases only milligrams instead of tens of grams for scintillation counting. Both cyclotron and tandem accelerator mass spectrometers have been used to accomplish this, with tandem accelerators becoming the most popular. One additional advantage of acceleration is that the ‘stripping process’ disassociates all molecular species with the result that carbon isotopes can be isolated, and contamination minimized. AMS ¹⁴C dating theoretically may push the time frame back to 100,000, effectively overlapping ⁴⁰Ar/³⁹Ar laser fusion dating (Taylor and Aitken 1997).

5. Radiation Dating Methods

As with most of the other types of dating methods, radiation dating methods have undergone tremendous advances in the last decade, although many of these methods remain somewhat controversial in their applications. Electron spin resonance (ESR) and thermoluminescence (both based on the accumulation of trapped electrons in minerals), and fission track dating (produced when alpha particles are created by spontaneous fission of ²³⁸U leaving a damage trail), have all had their detractors, but have recently gained recognition as techniques that are useful in dating materials not readily possible with the more accepted technology, for example glass, tooth enamel, and pigments (see Table 1). Archaeomagnetic dating has gained wide acceptance in many regions of the world and deserves some discussion.

5.1 Archaeomagnetic Dating

Archaeomagnetic and paleomagnetic dating both rely on the phenomenon of the frequent and predictable shifts in the Earth’s magnetic polarity in space and time. The premise for the method states that the Earth’s magnetic poles wander (show secular variation) or flip (reverse direction), and that these variations provide a temporal fingerprint that can be detected in rock and sediments. Iron dipoles in minerals in soft sediments align themselves parallel with the Earth’s magnetic field at the time of deposition until the sediment solidifies, for example as baked clay in a hearth. This creates detrital remnant magnetism whose direction and intensity precisely reflects the Earth’s magnetic field at the time of deposition; and by matching their magnetic orientation to a master record, it is possible to derive a relatively accurate date. This master curve has been derived for the last 10,000 years. Archaeomagnetism is useful in dating material, as appropriate, when other useful dating material, appropriate for other techniques is absent.

6. Chemical, Temperature, And Water Affected Dating Methods

Some of the more controversial dating methods are those that are based upon changes in chemicals, temperature, and or water for calibration. Amino acid racemization held great promise for dating organic materials, but is not generally reliable, while obsidian hydration dating, which was also promising, has become equally problematic.

6.1 Obsidian Hydration Dating

Obsidian, a quenched rhyolite glass is common along plate boundaries and volcanic arcs where crustal remelting has occurred. A glassy brittle rock with remarkable cutting properties, it has been used throughout human history in the production of stone tools (Shackley 1998). Obsidian is a noncrystalline glass, and therefore a disordered substance, and moves toward an ordered state by crystallization or, more precisely, perlitization (Friedman et al. 1997, Stevenson et al. 1998). This is accomplished by the absorption of water and a breaking of silicon and aluminum bonds, ultimately devitrifying the glass and forming perlite. As the process proceeds, an absorption front and hydration rim forms that theoretically occurs at a regular, linear rate through time. Measuring this rim with a petrographic microscope in microns theoretically yields an absolute date. On the surface, this would seem to be a remarkable method, resolving a number of dating issues in archaeological contexts in which organic datable material does not occur, but obsidian artifacts are abundant. More recently, the intervening negative effects of variable temperature and humidity through time have been found to influence the rate at which glass will hydrate. Due to this a number of researchers have rejected the method in toto (see Morgenstein et al. 1999, Ridding 1996). Still, a number of researchers have continued to utilize the method, and it has a number of devoted followers, even in the face of discrepancies between radiocarbon dates and obsidian hydration dates in the same stratigraphic position. Stevenson, and others have attempted to derive intrinsic hydration models based on the premise that each single obsidian nodule contains a different proportion of water than any other, and this will produce ages compatible with other dating methods (see Stevenson et al. 1998). Most do agree that obsidian hydration is a useful relative dating method which can be used to determine the extent of mixing in a stratigraphic column; given the model, one expects to see larger rim measurements at the bottom of a site than at the top. If this is not the case, then stratigraphic mixing is indicated. Obsidian hydration holds great promise, but most archaeologists are hesitant to include it in the arsenal of absolute dating methods.

Bibliography:

1. CALIB Radicarbon Calibration Software (2001) http://depts. washington.edu/qil/calib/
2. Carver M O H 1990 Digging for data: Archaeological approaches to data definition, acquisition and analysis. In: Francovich R, Manacorda D (eds.) Lo scavo archaeologica: della diagnosi all’edizione. Edizioni all’Insegna del Giglio, Firenze, Italy, pp. 45–120
3. Colcutt S N 1987 Archaeostratigraphy: A geoarchaeologist’s viewpoint. Stratigraphica Archaeologica 2: 11–18
4. Dean J S 1997 Dendrochronology. In: Taylor R E, Aitken M J (eds.) Chronometric Dating in Archaeology. Kluwer Plenum Publishers, New York, pp. 31–64
5. Farrand W R 1984 Stratigraphic classification: Living within the law. Quarterly Review of Archaeology 5: 1–5
6. Freeman A K L 1997 Middle to Late Holocene stream dynamics of the Santa Cruz River, Tucson, Arizona: Implications for human settlement, the transition to agriculture and archaeological site preservation. Ph.D. thesis, University of Arizona, Tucson, AZ
7. Friedman I, Trembour F W, Hughes R E 1997 Obsidian hydration dating. In: Taylor R E, Aitken M J (eds.) Chronometric Dating in Archaeology. Kluwer Plenum Publishers, New York, pp. 297–322
8. Goksu H Y, Oberhofer M, Regulla D 1991 Scientific Dating Methods. Kluwer Academic Publishers, Dordrecht, The Netherlands
9. Gregory D A, Adams J L (eds.) 1999 Excavations in the Santa Cruz River Floodplain: The Middle Archaic Component at Los Pozos. Center for Desert Archaeology, Tucson, AZ
10. Hard R J, Roney J R 1998 A massive terraced village complex in Chihuahua, Mexico, 3000 years before present. Science 279: 1661–4
11. Harris E C, Brown M R III, Brown G J (eds.) 1993 Practices of Archaeological Stratigraphy. Academic Press, London
12. Herz N, Garrison E G 1998 Geological Methods for Archaeology. Oxford University Press, Oxford, UK
13. Morgenstein M E, Wicket C L, Barkatt A 1999 Considerations of hydration-rind dating of glass artefacts: Alteration morphologies and experimental evidence of hydrogeochemical soil-zone pore water content. Journal of Archaeological Science 26: 1193–210
14. OxCal Radiocarbon Calibration Software (2001) http://units. ox.ac.uk/departments rlaha/orau/06/frm.htm
15. Rapp G Jr., Hill C L 1998 Geoarchaeology: The Earth Science Approach to Archaeological Interpretation. Yale University Press, New Haven, CT
16. Ridding R 1996 Where in world does obsidian hydration work? American Antiquity 61: 136–48
17. Shackley M S (ed.) 1998 Archaeological Obsidian Studies: Method and Theory. Kluwer Academic Plenum Publishing, New York
18. Shackley M S, Huckell B B, Huckell L W 2000 Late Preceramic farmer foragers at the foot of the Mogollon Rim: The McEuen Cave Archaeological Project Testing Report (AZ W:13:6 ASM). Report prepared for the Bureau of Land Management, Safford Area, AZ, US Department of Interior
19. Stein J K 1987 Deposits for archaeologists. Advances in Archaeological Method and Theory 11: 337–95
20. Stevenson C M, Mazer J J, Scheetz B E 1998 Laboratory obsidian hydration rates: Theory, method, and application. In: Shackley M S (ed.) Archaeological Obsidian Studies: Method and Theory. Kluwer Academic/Plenum Press, New York, pp. 181–204
21. Stuiver M, Reimver P J 1993 Extended ¹⁴C data base and revised CALIB 3.0 ¹⁴C age calibration program. Radiocarbon 35: 215–30
22. Taylor R E 2000 Science-based dating methods in historic preservation. In: Williamson R A, Nickens P R (eds.) Science and Technology in Historic Preservation. Kluwer Academic Plenum Press Publishers, New York, pp. 75–96
23. Taylor R E, Aitken M J (eds.) 1997 Chronometric Dating in Archaeology. Kluwer Academic Plenum Publishers, New York
24. Trigger B G 1989 A History of Archaeological Thought. Cambridge University Press, Cambridge, UK
25. US Congress, Office of Technology Assessment 1986 Technologies for Prehistoric and Historic Preservation, OTA-E-319. US Government Printing Office, Washington, DC
26. Waters M R 1992 Principles of Geoarchaeology: A North American Perspective. University of Arizona Press, Tucson, AZ