Chronological chart
This outline is intended as a brief guide to how the passage of time is comprehended in archaeological studies and also how accounts of Neolithic history are created by archaeologists from the remains, including structures, deposits, artefacts, and, for example, palaeo-environmental and laboratory analytical data, that they investigate. The outline discusses how chronologies (reckonings of the passage of time and dated sequences) are established and what they mean, historically and in terms of lived lives. It also provides a summary timeline that correlates developments in different parts of Britain across the centuries concerned.
This account of time as it affects our understanding of Neolithic life and history does not set out to survey all the different scientific dating methods used by archaeologists, nor does it explain in any detail the science behind them. Rather, it first provides some basic information about radiocarbon dating and its calibration, and about dendrochronology, since these are the techniques most commonly used, particularly in relation to the Neolithic period (other methodologies are more useful in addressing more ancient, or more recent, eras). It then discusses in general terms how archaeologists set about creating chronologies (meaning, in this context, interpretations of past sequences of activity) both within and between individual ‘sites’. It goes on to set out how historical narratives are derived from these chronologies, and how this relates to and compares with the temporalities (the varied scales and unfolding of time as they relate to lived experience in the past or the present) of individual and social existence. Finally, a chart is provided that maps (in simple terms) the elapsing of time against cultural development as set out especially in the narrative chapters of this book.
Radiocarbon dating (also termed ‘carbon-14 dating’) has been around now for many years, starting in the late 1940s when the American chemist Willard Libby originated a means of establishing how long ago a once-living organism expired and no longer absorbed carbon from the atmosphere. Most carbon comprises two isotopes, carbon 12 and carbon 13, and these are inherently stable. A very small percentage of carbon, however, comprises radiocarbon (carbon 14), and this is unstable, meaning that it decays. A living organism continues to absorb carbon 14 along with the other isotopes, so the lost amount is replenished. When the organism dies, however, the radiocarbon that it has absorbed when living reduces on its decay path logarithmically, and the rate of decrease is by one-half of the quantity at death every 5,730 years. It was Libby’s discovery that this decay is measurable against the elapsing of time since the organism’s death calculated against the constant of the amount of carbon in the Earth’s atmosphere that enabled ‘absolute’ dates to be calculated. As noted in Chapter 1, this revolutionized prehistoric chronology.
A complication was soon noted, however, in that objects in the Near East that were closely dated historically were found to have anomalous returns when dated by the radiocarbon method. This confirmed the suspicion that the ratio of carbon 14 to carbon 12 has varied through time, due to different quantities of carbon in the atmosphere through time (so causing variable rates of absorption). It was realized therefore, that to approximate ‘true dates’, the measurements in ‘radiocarbon years’ would need to be calibrated against the ring-counting of long-lived ancient trees, starting with California’s bristlecone pines. This produces a ‘dating curve’ that indicates the degree of variation from a standard mean through time. When linked to a calculation of probability for individual dates falling within the parameters of the curve at different points, this can provide a close estimate (through programmes such as INTCAL and OxCal) of the likelihood of the date from an individual sample falling within a span of as little as ten years in many cases. A refinement of the processing of carbon 14 samples, involving the application of Accelerator Mass Spectrometry (AMS), has meanwhile enabled much smaller entities, such as seeds, to return radiocarbon dates.
A north-west European tree-ring chronology has been built up by linking the ring-counts and patterns of growth-width from living trees back through an oak-based master chronology derived from archaeological or bog-oak samples. This enables dendrochronology to provide closely reliable radiocarbon calibration for the past 7,429 years in Ireland and 6,939 years in England. In detailed scientific reporting of the dating of radiocarbon samples from wood, bone, seeds, and other organic materials, the standard deviation is normally quoted at different probabilities. However, in books such as this a particular quoted date is stated only as ‘cal bce’ to indicate that this is a calibrated date. Dendrochronology not only depends upon the survival of wood that can be appropriately sampled, but also upon long enough series of growth-rings in trees to enable matching against the master-chronologies. The growth-ring pattern of oaks in western Britain has been highly susceptible to climatic variation through time, so producing more easily matched series. Dendrochronological dates are usually rendered as time before present (bp). Other techniques of dating applicable to the Neolithic period have been developed in recent decades that enable sequences of activity to be ‘bracketed’. An example is Optically Stimulated Luminescence (OSL) dating, which measures the last occasion when particular deposits were exposed to sunlight. See Mike Walker, Quaternary Dating Methods (Wiley, 2005) for details of radiocarbon, dendrochronology, OSL, and other methods.
Paradoxically, an archaeological ‘site’ is regarded by archaeologists as two different things. A site is both any locus of past activity (complex and apparently confined and coherent examples of which are routinely referred to as ‘monuments’), and any location that happens to be a focus for archaeological investigation (referred to in inventories of sites as an ‘archaeological event’ affecting the site concerned). So an archaeological ‘site’ can be either a place that witnessed activity that happened in the past, or a place of archaeological labours in the present (or recent past).
The chronology of a ‘site’ that existed in the past is created by archaeologists in both relative and absolute terms. The first is independent of any dating of the spans of time represented by the sequence of activity on that site, while the capacity to achieve the second depends upon the survival of organic or other material that can be sampled and that is therefore capable of returning a date. However, it is not just survival that matters in producing reliable determination of dates. First, the material to be sampled must relate to a particular event, such as, for example, the digging of a pit or an episode in its infilling; or the digging of a post-hole, the raising of a post within it, the withdrawal or the decay of that post in situ, or the burning of that post. And this context must have been sealed, that is, not affected by later disturbance or contaminating effects from soil processes, up until the point when archaeological excavation and the retrieval of the sample takes place. Moreover, the sample itself must be protected from modern contamination between the archaeological site and the laboratory.
In recent years the crucial importance of dating short-lived organisms, and bones that have entered the ground articulated together (and therefore discarded at a single point in time, rather than having derived from earlier deposits), has come to be fully appreciated. Further, it has been realized that the obtaining of a multiple series of samples taken from different contexts within the span of activity represented by the stratigraphic sequence within a site are vital to the creation of a reliable site chronology. It is this, combined with Bayesian statistical analyses, that identifies and hopefully removes ‘anomalous’ dates from the series, that has enabled the close estimates of the likely beginnings and endings of episodes of construction and abandonment of structures (components of monuments or major phases of activity) to be defined for sites like the long barrows or causewayed enclosures mentioned especially in Chapter 3 of this book.
How, then, do we correlate activity that has taken place, or patterns of change or development, between sites in different locations, to build up regional or supra-regional narratives? This is, of course, dependent in the first instance upon the availability of master-chronologies, and the increasing numbers of reliable radiocarbon determinations in different areas. So it continues to improve as more samples are retrieved and date-series and sequences are developed. To tighten the correlations and relate them to cultural sequences, it is helpful to be able to match these absolute dates recording closely similar practices and structures (for example) from different areas, and it is also helpful to be able to link artefacts with dated events and sequences. This is one reason why one of the most exciting developments of recent years has involved the dating of organic residues that have survived actually adhering to the surface of pots.
Historical narratives, as will have been evident from the main text of this book, can relate either to broad trends and the unfolding of cultural change across substantial spans of time and space, or to the intricacies of the trajectories of particular practices or cultural phenomena. For the former, what correlations between sequences of actions between sites, within regions, and across Britain as a whole enable is the identification of significant historical developments that otherwise might not be so evident. What this does not automatically imply, as we have been at pains to point out at various points in our account, is that change proceeds either very slowly or rapidly as a ‘wave of advance’. Rather, change occurs at different rates in different places, tending towards the stochastic (random, unpredictable), and with movements and moments that may be syncopated (with weaker or stronger pulses, abbreviated or extended durations) and/or staccato (with abrupt disconnections). The reasons for these discontinuities are human and social, and concern also the inheritance of cultural practices within descent groups. As a result a change that may be registered at one geographical location may be expressed simultaneously some distance away, while much of the cultural ‘landscape’ in between may be devoid of such indication. The reason for this ‘leap-frogging’ is best sought in the patterns of connectivity created and sustained through kinship ties and the time-honoured exchange of marriage partners between affines spread out across the landscape in the interstices of the settlements of other, non-related kin-groups.
For the latter, the correlations made between sites and sequences, aided by refined individual site chronologies and their comparison and summation, enable a more sophisticated understanding of pattern in changing practices. This, for example, makes it possible for archaeologists to move beyond the idea of ‘fashions’ (for instance for building particular kinds of tomb) to the correlation of trends in changing practices such as the beginning of the building, and the ceasing of the building, of trough-like chambers contained within large timber uprights in the first half of the fourth millennium.
Time as lived is complex. At its simplest, the elapsing of time is experienced within one’s own life-experience at its briefest as the time spent in performing an individual task, or engaging in a particular social intercourse (a conversation, for example). The lifespan of a transaction, however (such as the barter-exchange of a sheep for some timber, for example), can take place elastically—either completed within the span of a conversation or protracted over months or years. In this case, the passage of time is not that of time calibrated mechanically or digitally, but in terms of the understanding of change as lived, or more especially as reflected upon as time passes. Traditional societies, therefore, have a variety of mechanisms such as initiation (including coming-of-age ceremonies or entry into secret societies), age-grades (the identification of age-based cohorts), and extended mortuary ceremony (such as the practice of second-burial in which corpses are reprocessed and reburied at intervals of certain durations following decease) by which they reckon time’s passing. And they have developed social and historical devices through which ‘history’ has been both reckoned and expressed. Such devices include genealogy used for the reckoning of descent, and oral literature reflective of times past that have been used to register both significant events (such as volcanic eruptions or visitations of plague) and mythic individuals and histories.
Archaeological deposits and the artefacts retrieved from them ‘capture’ or embody these various contrasting temporalities. This means that although we may be limited in our means of representation of time either in narrative, or graphically, we are constantly dealing with the biographies not only of people (aided nowadays by the studies of dentition and DNA that we have mentioned at various points in the main text of this book) but of the objects they have created, used, and discarded.
It is extremely difficult, in the light of these complexities, to create simple graphic illustrations of the passage of time and the advent (let alone experiencing) of cultural changes. We do think, however, that it may be useful, especially for those readers less familiar with archaeological chronologies in general, and the British Neolithic in particular, to have a ‘ready-reckoner’ tabulation of change as registered in the currency (duration) of many of the individual cultural phenomena discussed in the book (see the chart on page 366).
At the top of this chart is a bar that gives an approximation of the elapsing of time reckonable via individual lifespans. In these terms, and using a standardized single generational turnover of twenty-five years, the period of ‘scientifically calibrated’ time from 4000 bce to 3500 bce would have witnessed twenty human generations (or approximated lifespans). This is the equivalent in modern British historical terms of the span between the dawning of the ‘Age of the Tudors (monarchy)’, and the mid twentieth-century ending of the Second World War. The elapsing of ‘absolute’ time is shown in the bar at the bottom of the chart. In totality, the period of approaching 2,000 years within which the Neolithic occurred witnessed the passing of eighty generations of people, approximating to the breadth of history from the birth of Christ (as registered in Christian calendars) and the present day.