Note: this is part of an electronic companion that supplements Kevin Greene's book Archaeology: an introduction (1995); click on the title to start from the home page.
'Dating is the key to organising all archaeological evidence. Furthermore, the development of dating methods, whether 'traditional' or scientific, illustrates the ingenuity and lateral thinking that make archaeological problem-solving such a fascinating exercise. ... At the beginning of the twentieth century it must still have been inconceivable that reliable dates could ever be established for European prehistory, other than those that depended on tenuous connections between Egypt and the Aegean in the second millennium BC. ... Not until 1950 did absolute dates become a reality for prehistoric archaeology in areas outside Scandinavia and the south-west of the United States, where varves and tree-rings had begun to provided a locally applicable dating method some decades earlier.' (p. 101)
'Ultimately archaeologists and historians share the same general objectives; the
principal contrasts lie in the kinds of evidence that they explore, and the different
aspects of the human past that they are able to address most successfully with the
material or documentary information available to them.' (p. 104)
NEW - Roman military sites in Britain 'A non-specialist's introduction to the fortresses, forts, watchtowers, temporary camps, depots and industrial sites, built by the Roman Army in Britain.' (Peter Green). Folow the link to military events to see maps of forts founded in different periods.
Thera and the Explosion A bibliography by Richard Foulkes about a knotty problem in dating a specific site, where historical and archaeological sources are not yet in agreement (Part of Chloris, a searchable bibliography of the Bronze Age archaeology of mainland Greece and Crete).
'Typology has not been superseded, but radiocarbon dates have reduced the burden of
prehistoric chronology that it was once made to carry (fig. 4.5). Type-series remain an
extremely useful means of describing and classifying artefacts of any period, and for
understanding their technology and function.' (p. 105)
'Seriation ... has been applied to finds from grave groups, strata, or other kinds of assemblages, whether found on individual sites or over a wider area. It works best on assemblages that contain a range of definable characteristics, such as types of pottery or flints, especially those that are subject to change rather than continuity. ... Seriation is only a relative dating method, but it remains useful in the study of finds that do not occur on stratified sites where the sequence is revealed by excavation; like artefact typologies, it is now used within an absolutely dated framework.' (p. 107)
'...archaeologists tend to forget that geology had already undergone a revolution in
scientific dating during the first half of the twentieth century. Seen in the context of the
development of dating methods over the previous century, radiocarbon does not seem
quite as dramatic as it is sometimes portrayed.' (p. 107)
Note: for the latest authoritative book on scientific dating see: R. E. Taylor and Martin J. Aitken, eds. Chronometric Dating in Archaeology. Advances in Archaeological and Museum Science, vol.
2. New York: Plenum Press, 1997. xix + 395 pp. Figures, tables, bibliographies, and index. $95.00 (cloth), ISBN 0-306-45715-6. There is also a comprehensive and detailed review:
Reviewed for H-NEXA by Charles C. Kolb, National Endowment for the Humanities,
(part 1),
(part 2).
'Nineteenth-century geologists were preoccupied with the age of the Earth, and Darwin's demand for gradual evolution underlined the length of the time-scales involved. ...estimates of geological time underwent a transition from informed guesswork to scientific precision in the fifty years that followed the publication of Darwin's Origin of Species in 1859. *Accurate knowledge of the age of the Earth was of little direct help to archaeologists, but it emphasised the potential of scientific dating techniques. The first half of the twentieth century witnessed a similar transition that began with the dating of recent geological periods when early humans first lived, and ended with the introduction of radiocarbon dating.' (p. 108-9)
'It had been recognised since at least the fifteenth century that trees produce annual
growth rings, and their physiology was well understood by the eighteenth century. ... Because annual growth rings are subject to seasonal factors that affect their thickness, distinctive patterns recognised in different samples of timber may be compared and used to establish their contemporaneity.' (p. 109)
'Sections cut through lake beds in glacial regions reveal a regular annual pattern of coarse and fine layers, known as varves. Variations in climate produced observable differences in the thickness of sediments, and, like the patterns of variation in tree-rings, this allows comparisons to be made between deposits in separate lake beds. ... Varves allowed the end of the last Ice Age to be dated with confidence to around 6800 BC and provided the first extension of 'calendar' dates into European prehistory.' (p. 112)
6.3 Pollen analysis
'Pollen that has accumulated in deep deposits such as peat-bogs supplies a sequential record of changes in vegetation since the last Ice Age, for variations in temperature and rainfall resulted in periods of markedly different plant and tree populations in the past. ... Since climatic zones established from pollen have been dated absolutely by radiocarbon, they are no longer required as chronological indicators; nevertheless, pollen analysis continues to supply important evidence for the interpretation of the ancient environment.' (p. 112-13)
Palynology Page University of Arizona: 'PALYNOLOGY is the branch of science dealing with microscopic, decay-resistant remains of certain plants and animals. It has many applications including archaeological palynology, Quaternary palynology, and stratigraphic palynology.' There are links to each of these topics.
6.4 Sea bed deposits
'Deep sediments exist on the sea-bed, representing a slow accumulation of shells and skeletal material from dead marine creatures. Cores ... extracted from these deposits reveal variations in oxygen isotopes in the shelly material, caused by fluctuations in the volume of the ocean that reflect global temperatures and ice ages. A pattern of climatic variation is derived from temperature-sensitive species of marine fauna and from measurements of oxygen isotopes. It correlates with geological evidence for cold and warm periods that are dated according to deviations in the Earth's orbit around the sun.' (p. 113)
Paleolimnology/Diatom Home
Pages Biology Department, Indiana University. These deal mainly with fresh-water rather than marine deposits, but the principles are similar.
6.5 Ice sheet cores
'Each winter's snowfall creates a distinct layer, and the annual layers have been counted back almost 6000 years in a core more than two kilometres in depth, with an excellent level of reliability within around 50 years... The thickness of each layer varies, as do the proportions of different oxygen isotopes whose formation is known to reflect temperature; thus, long-term patterns of variation reflect changes in climatic conditions. ... Some layers of ice contain high levels of dust and acidity caused by volcanic eruptions. Volcanoes known from historical records, such as Krakatoa (1883) or Vesuvius (AD 79), can be correlated with ice-cores; further undocumented eruptions in prehistoric times may also be detected.' (p. 113)
National Ice Core Laboratory University of Colorado: '...a facility for storing, curating, and studying ice cores recovered from the polar regions of the world'.
Mount St. Helens volcano A typical volcano that has a long history of eruptions - part of the superb Volcano World site
'...by 1950, a number of dating techniques had emerged that could offer chronological frameworks for the study of prehistory at least as reliable as those used by historical archaeologists. Unfortunately, all required special circumstances, such as the survival of timber for tree-rings, the proximity of glacial lakes for varves, or the existence of soil conditions that favoured the preservation of pollen. However, the successful development of dating methods for geological periods ... offered the possibility that a similar, generally applicable, technique might one day be found that would give absolute dates for prehistoric archaeology.' (p. 114)
7.1 Radioactive decay
'Several scientific dating techniques exploit the phenomenon of radioactive decay, including those first used to date the age of the Earth in the early years of the twentieth century. Many elements occur in different forms, and some are unstable; these isotopes have extra neutrons besides their standard number of protons and they are designated by a number representing their atomic weight (carbon-14 or 14C). Unstable isotopes are radioactive and emit rays of particles at a known rate. The speed of decay is expressed as the half-life, the time taken for half of the total radioactivity to decay; this may vary from seconds to millions of years.' (p. 114)
PRIME Lab Purdue Rare Isotope Measurement Laboratory: explanations of the principles of Accelerator mass spectrometry, and a wider look at the uses of radioacive isotopes.
7.2 Radiocarbon dating
'The rate of decay of carbon-14, which has a half-life of 5730 years, is long enough to
allow samples of carbon as old as 70,000 years to contain detectable levels of
radioactive emissions, but short enough for samples from periods since the late Stone
Age to be measured with reasonable precision. However, the feature of carbon-14 that
makes it exceptionally important is that it is absorbed naturally by all living organisms,
but ceases to enter them when they die.' (p. 115)
Radiocarbon This is the principal periodical for C14 dating - follow the links to further information and individual laboratories.
OCR Procedure for Dating Archaeological Features 'The effect of the biochemical degradation of charcoal and soil humic material can be measured by the ratio of the total carbon to the readily oxidizable carbon in the sample. This ratio is called the Oxidizable Carbon Ratio, or OCR.' (Douglas S. Frink)
7.3 Presenting and interpreting a radiocarbon date
'Because interpretation is so complex, all radiocarbon dates included in an
archaeological publication must be presented in a standard manner. ... Archaeologists must know exactly what is being dated and, in the case of samples from excavations, their precise stratigraphic relationship to the site. The nature of charcoal and wood samples is very important - twigs or nuts are ideal, because they only contain carbon-14 taken in during a short growing season, whereas the central portion of a large tree will obviously give a date decades (or even centuries) earlier than its use for fuel or construction.' (p. 119-21)
Calibration program"We are pleased to announce the HTML version of the radiocarbon program CALIB 4.2. ... Please refer to the on-line CALIB 4.1 manual for details about the calibration datasets and calculations. The HTML version uses the 1998 international radiocarbon calibration datasets..." (Paula Reimer & Minze Stuiver)
Der Tod startet die Stoppuhr Death starts the stop-watch: 'Everytime a living being dies a stop-watch starts ticking. Science can read this watch and thus determine the age of a find.' A superbly illustrated description of radiocarbon dating from WebMuseen (Germany)
7.4 Potassium-argon dating
'...so few radioactive carbon-14 isotopes remain in a sample more than 40,000 years old
that it is difficult to measure the small number of particle emissions. The technique is
therefore unsuitable for studying most of the Palaeolithic period; fortunately, a related
method based on an isotope of potassium allows the examination of early hominid
developments beyond the range of radiocarbon.' (p. 122)
7.5 Uranium series dating
'Thorium-230 is a useful isotope because it has a half-life of 75,400 years. Although coral
is the ideal sample material, calcite crystals contained in stalagmite may also be sampled, and this makes it suitable for dating early human activity in caves, anywhere between 5000 and 350,000 years ago... In any case, the precise relationship between the sample and an archaeological event or activity must always be established. Uranium series dating is frequently used in conjunction with ESR (electron spin resonance), for the latter may also be carried out on the kinds of samples typical of cave finds, such as teeth, shells and
stalagmite calcite.' (p. 123)
'The following absolute techniques do not simply measure radioactive emissions or the
products of radioactive decay; instead, they examine the effects of radioactive impurities
on the crystal structure of minerals.' (p. 123)
8.1 Thermoluminescence dating
'The most important material for TL is fired clay; hearths, kilns and especially pottery
form an important part of the archaeological record in most parts of the world. Since pots
are fired at a temperature well above that required to release all the electrons that have
been trapped in their crystal lattices, the energy released in the laboratory today will
have built up from the date of their firing. The older the pots, the more energy that should
have accumulated.' (p. 123)
Luminescence Dating Laboratory, Aberystwyth 'The method was initially developed in the 1960's for dating pottery. However, since 1979 the method has also been applied to dating geological sediments, and this is the application that has been worked upon most extensively in the Aberystwyth luminescence laboratory. The method can produce ages from as low as 30-50 years, up to almost a million years'.
Optically Stimulated Luminescence (OSL) dating Sheffield Centre for International Drylands Research: 'OSL is a relatively new alternative approach to chronological problems. Both quartz and feldspar rich sediments, which are otherwise undateable by conventional radiocarbon methods, can be absolutely dated (± ~10%) within a range of 100 to 200,000 years.'
8.2 Electron spin resonance ('ESR')
'...ESR has much in common with thermoluminescence, for both measure electrons that have become trapped in the crystal lattice of minerals. It differs from TL in the nature of suitable samples, which include teeth, shells and stalagmite calcite. ... ESR sample materials favour the study of the Palaeolithic period, for stalagmites may be related to cave occupation, and fossil teeth from large mammals such as mammoths may provide effective dating.' (p. 124-5)
'This method involves counting microscopic damage trails in minerals such as zircon, and glass, whether volcanic (e.g. obsidian) or of human manufacture. The trails are caused by fission fragments when the nucleus of uranium-238 splits during radioactive decay. ... Fission-track dating, along with potassium-argon, has also assisted in checking the age of volcanic deposits associated with early hominid remains in East Africa.' (p. 125)
'...the level of thorium-230 found in a sample of stalagmite is a product of its uranium content, and the sample's age is calculated from the known radioactive half-life of thorium-230, which is not affected in any way by its environment; this method can therefore be described as absolute. In contrast, measurement of one form of amino acid changing to another is a derivative method, for the rate of alteration is entirely dependent on the temperature of the context where the sample has been buried.' (p. 125)
9.1 Fluorine, uranium and nitrogen tests
'Buried bone absorbs water containing elements that react chemically with the bone,
adding fluorine and uranium, while nitrogen decreases through the decay of bone protein
(collagen). Bones found in a single context should have been subjected to the conditions
that cause these changes in a uniform manner, and their levels of these three elements
should therefore be very similar. Older survivals and recent intrusions should therefore
be distinguishable because of unusually high or low levels.' (p. 125)
9.2 Amino acid racemization
'Samples taken from bone, teeth or shells contain detectable amino acids that undergo
gradual change (racemization) from L-form to D-form over time; the ratio of the two is
measured to indicate age. Since the rate of change is highly dependent on temperature it
is necessary to use an independent method, such as radiocarbon, to date a sample from
the same burial context. Once this has been done, the speed of racemization may be
determined and other samples may be dated by this means alone.' (p. 126)
9.3 Obsidian hydration dating
'Obsidian is a natural volcanic glass that was a popular alternative to flint for making flaked tools in many parts of the world. As soon as a fresh surface of obsidian is exposed, for example during the process of making it into a tool, a microscopically thin 'hydration rim' begins to form as a result of the absorption of water. Furthermore, obsidian from different geological sources may weather at different rates.' (p. 126)
'Fine grains of iron oxide are present in most clay and soil, and they take on a new magnetic alignment in two main ways. Thermoremanent magnetism is acquired when they realign according to the Earth's magnetic field after having been disoriented by heating above 650 degrees C; some grains may retain the new field for hundreds of thousands of years. Magnetism is also acquired by means of the deposition of sediments, for instance in lake beds, where particles may settle into alignment with the prevailing magnetic field. ... Magnetic dating measures the alignment in an ancient sample and attempts to relate it to
a record of past changes in the magnetic field.' (p. 127)
9.5 Cation-Ratio dating ('CR')
'Prehistoric rock carvings (petroglyphs) ... are commonly covered by a so-called 'rock varnish', a chemically changed layer that builds up after around 100 years through weathering, enhanced by the action of micro-organisms. ...samples are taken by scraping the 'varnish' from petroglyph surfaces back to original rock surface. A separate cation (positively charged ion) leaching curve must then be established for different geographical areas, because local soil and moisture conditions affect the speed of its formation.' (p. 128)
Rock Art World-wide list of links including Europe, the US, India, and Australia
'It is inevitable that major museums that buy items for their collections become involved
in expensive commercial dealings in the fine art market. The profits to be made not only
stimulate illicit plundering of ancient sites, but encourage skilful forgeries. Scientific
dating techniques bring obvious benefits, for precise dates are rarely required, simply
an assurance that an artefact is not a modern fake.' (p. 129)
'Traditional forms of archaeological dating have been strengthened immeasurably by the
growth of an extraordinarily diverse range of scientific techniques that helps to
demonstrate the truly multi-disciplinary nature of modern archaeology. Traditional
methods have not been replaced, however. The definition of sequences by
means of stratigraphic excavation remains the basis for observations about sites and for
typological studies of artefacts. Scientific dating techniques add precision and allow
specific hypotheses about the relationships of sites, regional cultures or forms of
artefacts to be tested.' (p. 129)
Please remember that all paragraphs of text from my book included in this web site are copyright, and should not be quoted without acknowledgement or copied without my permission.
