Archaeologists, on the other hand, provide proof of authenticity of a certain artifact or debunk historical or anthropological findings. Studying the material remains of past human life and activities may not seem important or exciting to the average Joe unlike the biological sciences. It is in knowing what made past cultures cease to exist that could provide the key in making sure that history does not repeat itself. Over the years, archaeology has uncovered information about past cultures that would have been left unknown had it not been with the help of such technologies as radiocarbon dating, dendrochronology , archaeomagnetic dating, fluoride dating, luminescence dating, and obsidian hydration analysis, among others.
Radiocarbon dating has been around for more than 50 years and has revolutionized archaeology. Carbon 14 dating remains to be a powerful, dependable and widely applicable technique that is invaluable to archaeologists and other scientists. The unstable and radioactive carbon 14, called radiocarbon, is a naturally occurring isotope of the element carbon.
When a living thing dies, it stops interacting with the biosphere, and the carbon 14 in it remains unaffected by the biosphere but will naturally undergo decay. Decay of carbon 14 takes thousands of years, and it is this wonder of nature that forms the basis of radiocarbon dating and made this carbon 14 analysis a powerful tool in revealing the past.
The process of radiocarbon dating starts with the analysis of the carbon 14 left in a sample. Calibration is then done to convert BP years into calendar years.
AMS Carbon Dating Lab Pretreatment Protocols
This information is then related to true historical dates. Before deciding on using carbon dating as an analytical method, an archaeologist must first make sure that the results of radiocarbon dating after calibration can provide the needed answers to the archaeological questions asked. The implication of what is represented by the carbon 14 activity of a sample must be considered. The sample-context relationship is not always straightforward. Date of a sample pre-dates the context it is found.
Some samples, like wood, already ceased interacting with the biosphere and have an apparent age at death and linking them to the age of the deposits around the sample would not be wholly accurate. There are also cases when the association between the sample and the deposit is not apparent or easily understood. Great care must be exercised when linking an event with the context and the context with the sample to be processed by radiocarbon dating.
An archaeologist must also make sure that only the useful series of samples are collected and processed for carbon dating and not every organic material found in the excavation site.
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- Pretreatment and Contamination;
It is important that the radiocarbon scientists and archaeologists agree on the sampling strategy before starting the excavation so time, effort, and resources will not be wasted and meaningful result will be produced after the carbon dating process. The constituents of bone include proteins , which contain carbon; bone's structural strength comes from calcium hydroxyapatite , which is easily contaminated with carbonates from ground water.
Removing the carbonates also destroys the calcium hydroxyapatite, and so it is usual to date bone using the remaining protein fraction after washing away the calcium hydroxyapatite and contaminating carbonates. This protein component is called collagen. Collagen is sometimes degraded, in which case it may be necessary to separate the proteins into individual amino acids and measure their respective ratios and 14 C activity.
It is possible to detect if there has been any degradation of the sample by comparing the relative volume of each amino acid with the known profile for bone. If so, separating the amino acids may be necessary to allow independent testing of each one—agreement between the results of several different amino acids indicates that the dating is reliable. Hydroxyproline , one of the constituent amino acids in bone, was once thought to be a reliable indicator as it was not known to occur except in bone, but it has since been detected in groundwater.
Waikato Radiocarbon Dating Laboratory
For burnt bone, testability depends on the conditions under which the bone was burnt. The proteins in burnt bone are usually destroyed, which means that after acid treatment, nothing testable will be left of the bone. Degradation of the protein fraction can also occur in hot, arid conditions, without actual burning; then the degraded components can be washed away by groundwater. However, if the bone was heated under reducing conditions , it and associated organic matter may have been carbonized. In this case the sample is often usable. Shells from both marine and land organisms consist almost entirely of calcium carbonate, either as aragonite or as calcite , or some mixture of the two.
Calcium carbonate is very susceptible to dissolving and recrystallizing; the recrystallized material will contain carbon from the sample's environment, which may be of geological origin. The recrystallized calcium carbonate is generally in the form of calcite, and often has a powdery appearance; samples of a shiny appearance are preferable, and if in doubt, examination by light or electron microscope, or by X-ray diffraction and infrared spectroscopy, can determine whether recrystallization has occurred. In cases where it is not possible to find samples that are free of recrystallization, acid washes of increasing strength, followed by dating part of the sample after each wash, can be used: Contaminated samples, naturally, will have inaccurate results.
Sample Contamination and Pretreatment
The specific effect of the contaminant on radiocarbon dating results depends on the type of contaminant, the degree of contamination, and the relative ages of the sample and the contaminant. Limestone is of geological origin and would be much older than any archaeological sample; hence, inclusion of limestone during the carbon 14 dating would make the sample older than its true age. Humic and fulvic acids are naturally present in soil where microbial degradation of plants and animals has occurred.
The effect of these organic acids on the sample, whether they would make the sample older or younger, depends on the age of their original organism.
When roots of plants penetrate wood, charcoal, soil, or bones, modern carbon is already introduced to them. This occurrence can make the samples seem younger than their true age. The degree of contamination affects the magnitude of the inaccuracy in the carbon 14 dating results. In general, infinite-age contamination can make a sample considerably older while modern contamination can make the sample significantly younger than its true age. Regardless of the carbon dating methodology employed, be it radiometric dating or the accelerator mass spectrometry AMS method , a process must be done before analysis to get rid of all possible contaminants.
This process is called pretreatment. Radiocarbon dating labs receive various materials for analysis but not all portions of the samples can be used. It must be noted that radiocarbon dating is only applicable to materials that were once part of a living organism. Bones, shells, wood, charcoal, peat, linen, wool, and parchment are the common materials submitted for radiocarbon testing.
Metal and stones cannot be directly dated unless they have organic materials embedded in them.
There is no standard method for pretreatment applicable to all samples for radiocarbon dating. The pretreatment method employed depends on the type of sample and the possible contaminants.
Radiocarbon dating labs must therefore be informed of the environmental conditions and preservation techniques done to the sample before carbon analysis. There are two types of pretreatment usually applied to samples for carbon dating—physical and chemical. The physical pretreatment of samples for radiocarbon dating is generally done by removing contaminants without the use of chemicals followed by the reduction in sample size.
Physical pretreatment usually involves the removal of rootlets that intruded on the sample using tweezers or forceps. This is a straightforward method for most samples sent to carbon dating labs except for peat samples that have been dried where the rootlets may not be easily distinguished from the rest of the sample. Another physical pretreatment done on samples for carbon dating involves the removal of contaminants by scraping off the exterior layers using the applicable equipment.
Related radiocarbon dating samples
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