Old wood
Encyclopedia
The old wood effect or old wood problem is a pitfall encountered in the archaeological
technique of Carbon 14 dating. A sample will provide misleading or confusing results if materials of different ages are deposited in the same context
.
Stratification
is not always clear cut in practice. In the case of dating megalithic tombs, indirect evidence for the age of the tomb must always be obtained, because stone (or the time of moving a stone) can not be dated. When a number of objects are recovered from one deposit, the terminus post quem
is based on the dating from the 'youngest' find. Even though other items in the same stratum indicate earlier dates, they may have been deposited at the same time. The deposit must be as young, or younger than the youngest object it contains. Thus excavators look to post holes, pits, or find spots under the orthostats for clues to construction dates. The possibility that something (organic) was already in situ must always be considered, especially if the results appear suspiciously early.
The old wood problem can appear in marine archaeology. Researchers need to check if stumps from a Mesolithic
or Palaeolithic submerged forest
are to be found in the area (If they do, the possibility of one sticking up through - for example - a shipwreck and giving misleading dates must be considered).
When radiocarbon ages are combined - especially in instances where samples do not come from the same part of one organism - problems can arise. If compelling archaeological reasons for supposing that the ages come from exactly contemporary samples do not exist then results must be regarded as suspect. If there exists no prior reason to believe that two samples are truly of the same age and even if their ages are statistically indistinguishable, they are as likely to be as far apart in true age as the measured difference between them as they are to be of the same age.
Charcoal
turns out, for many reasons, to be an ideal medium for carbon dating. When long-lived tree species such as oak
and juniper
, are used, however, there is a particular danger of encountering the 'old wood' problem. For example; the date you are measuring may be from heartwood already many centuries old by the time the tree was cut down. Another difficulty is that of possible time-lags between felling and final deposition. The timber may have had an extensive history of use and re-use. An ideal material to date, if available, would be twigs of such trees as hazel
.
And of course, the old adage of 'one date is no date' always applies. A representative spread of dates is required before interpretation can be attempted.
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
technique of Carbon 14 dating. A sample will provide misleading or confusing results if materials of different ages are deposited in the same context
Archaeological context
In archaeology, not only the context of a discovery is a significant fact, but the formation of the context is as well. An archaeological context is an event in time which has been preserved in the archaeological record. The cutting of a pit or ditch in the past is a context, whilst the material...
.
Stratification
Stratification (archeology)
Stratification is a paramount and base concept in archaeology, especially in the course of excavation. It is largely based on the Law of Superposition...
is not always clear cut in practice. In the case of dating megalithic tombs, indirect evidence for the age of the tomb must always be obtained, because stone (or the time of moving a stone) can not be dated. When a number of objects are recovered from one deposit, the terminus post quem
Terminus post quem
Terminus post quem and terminus ante quem specify approximate dates for events...
is based on the dating from the 'youngest' find. Even though other items in the same stratum indicate earlier dates, they may have been deposited at the same time. The deposit must be as young, or younger than the youngest object it contains. Thus excavators look to post holes, pits, or find spots under the orthostats for clues to construction dates. The possibility that something (organic) was already in situ must always be considered, especially if the results appear suspiciously early.
The old wood problem can appear in marine archaeology. Researchers need to check if stumps from a Mesolithic
Mesolithic
The Mesolithic is an archaeological concept used to refer to certain groups of archaeological cultures defined as falling between the Paleolithic and the Neolithic....
or Palaeolithic submerged forest
Submerged forest
Submerged forest is a term used to describe the remains of trees which have been submerged by marine transgression, i.e. sea level rise and petrified. Examples can be found at low tide on the fringes of the submerged landmass known as Doggerland, around the coast of England and Wales, the Channel...
are to be found in the area (If they do, the possibility of one sticking up through - for example - a shipwreck and giving misleading dates must be considered).
When radiocarbon ages are combined - especially in instances where samples do not come from the same part of one organism - problems can arise. If compelling archaeological reasons for supposing that the ages come from exactly contemporary samples do not exist then results must be regarded as suspect. If there exists no prior reason to believe that two samples are truly of the same age and even if their ages are statistically indistinguishable, they are as likely to be as far apart in true age as the measured difference between them as they are to be of the same age.
Charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
turns out, for many reasons, to be an ideal medium for carbon dating. When long-lived tree species such as oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
and juniper
Juniper
Junipers are coniferous plants in the genus Juniperus of the cypress family Cupressaceae. Depending on taxonomic viewpoint, there are between 50-67 species of juniper, widely distributed throughout the northern hemisphere, from the Arctic, south to tropical Africa in the Old World, and to the...
, are used, however, there is a particular danger of encountering the 'old wood' problem. For example; the date you are measuring may be from heartwood already many centuries old by the time the tree was cut down. Another difficulty is that of possible time-lags between felling and final deposition. The timber may have had an extensive history of use and re-use. An ideal material to date, if available, would be twigs of such trees as hazel
Hazel
The hazels are a genus of deciduous trees and large shrubs native to the temperate northern hemisphere. The genus is usually placed in the birch family Betulaceae, though some botanists split the hazels into a separate family Corylaceae.They have simple, rounded leaves with double-serrate margins...
.
And of course, the old adage of 'one date is no date' always applies. A representative spread of dates is required before interpretation can be attempted.