Feb 09, · Radiocarbon dating is a technique used by scientists to learn the ages of biological specimens – for example, wooden archaeological artifacts or ancient human remains – from the distant past Author: Earthsky. Carbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis.. Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere.
How Does Carbon Dating Work Carbon is a weakly radioactive isotope of Carbon; also known as radiocarbon, it is an isotopic chronometer. C dating is only applicable to organic and some inorganic materials not applicable to metals. Gas proportional radioactive carbon dating is useful for the past, liquid scintillation counting and accelerator mass spectrometry are the three gor radiocarbon dating methods. What is Radiocarbon Dating? Radiocarbon dating is a method that provides objective age estimates for carbon-based materials that originated from living organisms. The impact of the radiocarbon dating technique on modern man has made it one of the most significant discoveries of the 20th century. Archaeology and cadbon human sciences use radiocarbon dating to prove or disprove theories.
Carbon 14 is continually being formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms.
It is rapidly oxidized in air to form carbon dioxide and enters the global carbon cycle. Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes.
When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay. Radiocarbon dating is essentially a method designed to measure residual radioactivity. By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known.
It must be noted though that radiocarbon dating results indicate when the organism was alive but not when a material from that organism was used. Measuring Radiocarbon — AMS vs Radiometric Dating There are three principal techniques used to measure carbon 14 content of any given sample— gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry. Gas proportional counting is a conventional radiometric dating technique that counts the beta particles emitted by a given sample.
Beta particles are products of radiocarbon decay. In this method, the carbon sample is first converted to carbon dioxide gas before measurement in gas proportional counters takes place. Liquid scintillation counting is another radiocarbon dating technique that was popular in the s. In this method, the sample is in liquid form and a scintillator is added. This scintillator produces a flash of light when it interacts with a beta particle.
A vial with a sample is passed between two photomultipliers, and only when both devices register the flash of light that a count is made. Accelerator mass spectrometry AMS is a modern radiocarbon dating method that is considered to be the more efficient way to measure radiocarbon content of a sample.
In this method, the carbon 14 content is directly measured relative to the carbon 12 and carbon 13 present. The method does not count beta particles but the number of carbon atoms present in the sample and the proportion of the isotopes. Carbon Datable Materials Not all materials can be radiocarbon dated.
Most, if not all, organic compounds can be dated. Samples that have been radiocarbon dated since the inception of the method include charcoal , wood , twigs, seeds , bones , shells , leather, peat , lake mud, soil , hair, pottery , pollen , wall paintings, corals, blood residues, fabrics , paper or parchment, resins, and water , among others.
Physical and chemical pretreatments are done on these materials to remove possible contaminants before they are analyzed for their radiocarbon content. Carbon Dating Standards The radiocarbon age of a certain sample of unknown age can be determined by measuring its carbon 14 content and comparing the result to the carbon 14 activity in modern and background samples.
The principal modern standard used by radiocarbon dating labs was the Oxalic Acid I obtained from the National Institute of Standards and Technology in Maryland. 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. This information is then related to true historical dates. Is Carbon Dating the Right Method? 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. Radiocarbon Scientists—Archaeologists Liaison 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.
It must be stressed that archaeologists need to interact with radiocarbon laboratories first before excavation due to several factors. Sample type, size and packing Laboratories have limitations in terms of the samples they can process for radiocarbon dating. Some labs, for example, do not date carbonates.
Laboratories must also be consulted as to the required amount of sample that they ideally like to process as well as their preference with certain samples for carbon dating.
Other labs accept waterlogged wood while others prefer them dry at submission. Sample collection Contaminants must not be introduced to the samples during collection and storing. Hydrocarbons, glue, biocides, polyethylene glycol or polyvinyl acetate PVA must not come in contact with samples for radiocarbon dating.
Other potential contaminants include paper, cardboard, cotton wool, string and cigarette ash. Sample storage Samples must be stored in packaging materials that will protect them during transport and even during prolonged storage.
Labels attached to the packaging materials must not fade or rub off easily. Glass containers can be used when storing radiocarbon dating samples, but they are susceptible to breakage and can be impractical when dealing with large samples. Aluminum containers with screw caps are safe, but it is still best to consult the radiocarbon laboratory for the best containers of carbon dating samples. Errors and calibration It is recommended that archaeologists, or any client in general, ask the laboratory if results have systematic or random errors.
They should also ask details about the calibration used for conversion of BP years to calendar years. Cost Clarify the costs involved in radiocarbon dating of samples.