Isotope analysis is the examination and identification of isotopic signatures or the distribution of stable isotopes within chemical compounds. In archaeology it is useful when applied to the food web, making it possible to acquire direct estimates concerning diet, tropical level and subsistence.
Scottish Nobel Prize Winner
One fine Scottish day in 1913, Dr Margaret Todd was discussing chemistry matters with her distant relative, Fredrick Soddy. Soddy was a chemistry scientist at Glasgow University and was explaining to Margaret that from his investigations it appeared as if numerous elements of the periodic table occupied the same position. Margaret suggested that all good chemical discoveries should have a Greek name and she offered the Greek word for ‘at the same place’ as suitable to describe the discovery. Soddy was pleased to use it and, in 1921, went on in his career to win the Nobel Prize for Chemistry.
Carbon, Nitrogen and Oxygen in Palaeodiets
The palaeontologist or the archaeologist, at an archaeological excavation, may discover whole bones or bone fragments from human or animal species. These bones can be consulted to provide assumptions about the diet (known as a palaeodiet) of their ancient owner. Bone, recovered from archaeological sites, can be used to gather information about original diet and possible migration trends by analysing the samples isotopically.
The nitrogen and carbon compositions within the target bone sample are used to reconstruct possible diet while oxygen isotopes provide data used to determine geographic location and origin. Oxygen isotopic analysis utilises what is called the hydroxyl group.
It is always important for analysts to understand the processes of diagenesis that can affect the original isotopic signal in order to obtain an accurate representation of palaeodiets.
Archaeology and Anthropology
Teeth, recovered from archaeological digging sites, can also be analysed. The enamel of teeth and also the immediate soil or matrix that they are discovered in (specially soil still clinging to the tooth) can be used in isotope analysis, therefore, archaeologists and/or palaeontologists will take great care when retrieving bone remains from the floor of the dig to ensure that the maximum analysable material is brought back to the laboratory.
Because isotopic oxygen is introduced into the body through ingestion, archaeologists can measure the oxygen incorporated into the hydroxylcarbonic appetite of tooth enamel. Teeth, unlike other bones, are not remodelling continuously throughout the organism’s lifetime and their isotopic oxygen ratios will remain constant from the time of their maturation.
Teeth are relatively resistant to physical and chemical changes due to environmental factors over time, but they remain vulnerable to post-depositional diagenesis. For this reason isotopic analysts show preference for the more resistant phosphate groups over the abundant diagenetic carbonate or the plentiful hydroxyl groups.
The Science of Isotope Analysis
Isotopes imbue animals and humans during their lifetime via eating, drinking, and the inhalation of particles. The imbued isotope process ceases with the death of the creature, and from this point isotopes no longer accumulate in any tissue or body remnant. However, as isotopes do undergo degradation, it is preferable for accurate results, for the researcher to know with some certainty the original timeframe and in particular a good estimation of the isotopes present at the time of death.
Isotope analysis is a very specialised branch of science and it is highly unlikely that any archaeological excavation will host a resident analyst. University laboratories are where most of the isotope analysis will be performed and experts will analyse the material brought by archaeologists for them to investigate and provide expert opinions about diet, subsistence and origin.