Artefacts methods dating face she
Monday, September 18, 2017 by Bone
There are a variety of methods and processes available to archaeologists for the dating of sites and artefacts and in this essay, I shall attempt to review a small selection of these methods, giving a description of how the method works, and the reliability of the results obtained.
There are two overall types of dating: Relative and Absolute. Relative dating is not as accurate as absolute dating, but I shall look at methods from both areas. I will start by looking at relative dating methods.
Relative dating involves ordering things into sequences. The ‘things’ can be artefacts or immaterial things that might occur within the environment. Possibly the simplest method of relative dating is the depth at which artefacts are found. This is called Stratigraphy. Stratigraphy is the study of stratification – the laying down of strata or layers (also called deposits) (Renfrew 2000).
[Figure 1: Strata in the Earth]*
At the bottom of these layers is bedrock. As time progresses, these layers build up one on top of another, providing a relative chronological sequence from bottom (earliest) to top (latest). These layers are distinguishable due to the colour and texture of the soil. When an item is found, it is labelled and details recorded on the label one of which is the depth at which it was found. This gives a very rough idea of the age in which the artefact was deposited. The composition of the soil and rocks found in the layer of interest are also analysed. Fossils can also be found, contained within the rocks, which can also give clues when estimating the period in time.
Another method of relative dating is Pollen Dating. This method uses pollen that has been trapped in bogs, lake sediments and in the strata in the earth. As I have already said, relative dating works by organising things into sequences. Pollen can be organised into such a sequence and this sequence is broken down into areas called zones, in this particular case, pollen zones. As pollen is virtually indestructible, it exists for great lengths of time, meaning we can age a site to as far back as three million years ago. However, the main problem with aging a site by pollen is that the zones are not the same for every site. This means that in most cases, where it is an advantage to age by pollen, it is often better to work with a specialist, who can identify the pollen zones native to that locale.
Absolute dating is far more accurate than relative dating. Absolute dating methods are used when archaeologists wish to know how old an artefact or site is in calendar years. Absolute dating methods range from traditional methods to up-to-date scientific methods.
One of the more traditional methods of absolute dating is Dendrochronology. This involves counting the number of rings in timbers. Every year, most trees grow a new ring of wood, which causes visible rings in a cross-section of a tree. These rings vary in thickness, due to the conditions of that particular year, making this method of dating useful as it tells us that little bit more, other than the age. If the year was a warm, wet year, then the ring in the tree will be thicker then the average diameter, whereas if the year was a cold, dry year, then the band will be thinner than the average diameter.
[Figure 2: Age rings in an Oak tree]*
In order to use dendrochronology, things called tree-ring chronologies have to be constructed for use as references. These are produced by overlapping ring patterns from successively older timbers, starting with living trees, then buildings, and finally samples from archaeological sites and peat bogs. (Sheffield Dendrochronology Laboratory, 2002).
One problem with dendrochronology however, is that different trees grow in different places, and so, as with pollen dating, it often pays to consult a specialist when utilising this method of dating. Another problem is that although there are ‘master sequences’ for different trees in different places, sometimes, local chronologies remain ‘floating’, that is, they have not been included into the master sequences, although this is slowly becoming less of a problem.
The process for dating a timber sample goes like this: first, the rings are measured and the pattern is searched for in the reference chronologies, to hopefully yield a match. Each ring in the sample can then be dated. The degree of accuracy to which a timber sample is dated increases if bark is present as the ring before the bark is the year in which the tree was felled.
A much more up-to-date method of aging artefacts (although dendrochronology is within the past fifty years), is Carbon-14 (14C) dating. Every living thing has a percentage of 14C in it and this amount remains constant while the animal or plant is alive because the uptake of 14C is equal to its rate of decay. However, once the organism dies, the quantity of 14C begins to decrease. It is this ‘feature’ that allows us to date an artefact by measuring the amount of 14C left in the item. However, there are still problems with this method. One of these is that 14C has a half-life of 5568 years. This means that carbon dating can only be used effectively with artefacts older than five thousand years. Another problem is that there has to be some organic material at the site in question, because, as I have already mentioned, Carbon-14 only exists in organic materials. Other than these two problems, carbon dating can be used for just about any artefact.
In conclusion, there are many different ways of aging artefacts and sites, some of which are more effective than others, although each method has an up and a down side. The process used is dependent on whether a relative date or an absolute date is required, and in some cases, the reliability of the method can also depend upon the experience of the person or persons carrying out the process.
Renfrew, C. and Bahn, P. 2000 Archaeology: Theories Methods and Practice, Thames and Hudson
Hawcroft, J. 2002 Unpublished Lecture Notes, University of Central Lancashire
Watson, J. Sheffield Dendrochronology Laboratory,
Ask Yahoo!: How does carbon dating work?,
Stratigraphy on Encyclopedia.com, 2002