Archaeology Essay, Research Paper
The subject of archeology can open up the yesteryear to us in a manner in which we can come in into a duologue with our ascendants. There are many ways it can make this: stratigraphic digging, clayware typology, socio-historic reading, etc. However, one yarn running through this progressively focussed chase is that of dating the physical findings to a peculiar cultural timeline. This is important if we are to cognize, with every bit much certainty as is allowed, who we are talking with.
Indeed, dating may be the proverbial yarn that holds full chase together, without which the person pieces of the mystifier might be compared to the kids of Israel, who the writer of Judges describes as each traveling off in their ain way. Like the male monarch Judges so wistfully imagines, dating brings coherence and way to a potentially ( or existent? ) helter-skelter state of affairs. In this paper I will research the specifics of carbon 14 dating ; from its background and beginning, to treatment of samples, method, consequences, and calibration.
Background With the detonations of the first atomic bombs repeating in his ideas, Willard F. Libby, working with A.V. Grosse, Ernest Anderson, and several pupils, pioneered the work on a theory that natural C14 non merely existed, but that it could besides be used as a method for dating certain artefacts of antiquity. Working under the premiss of his 1946 paper that suggested C14 might be in all life beings, a squad including Libby and Grosse collected readings from the Baltimore cloaca system. It was discovered that methane collected from these cloacas contained carbon 14 activity, whereas methane derived from crude oil did non. These findings gave strength to the theory suggested in his paper, but several old ages of extra research were needed. After their cloaca experiments, planetary samples of wood were gathered in which the research workers discovered a consistent degree of carbon 14 sedimentations. From that point on, the theory developed until it became widely accepted within the scientific community, climaxing with Libby? s credence of the Nobel award for chemical science in 1960.The Beginning of C14 Natural C14 is formed in the upper atmosphere when N reacts with neutrons. Neutrons are produced by cosmic beams pelting the Earth, and are therefore dependent upon the degree of cosmic beam barrage, every bit good as the Earth? s natural ability to have the beams from infinite. The lone known hindrance to cosmic beam soaking up is the Earth? s magnetic field. The stronger it is, the less the cosmic beams reach the Earth. Once the C14 is produced, it exists in a really little measure in C dioxide, a merchandise of O and C. From here, all life beings take in C14 by either photosynthesis ( works life ) or the nutrient concatenation ( take a breathing life ) . Since C14 is radioactive, and hence destructive to life, it is necessary for all beings to let go of C14 at fundamentally the same rate they consume it. Those that do non let go of radioactive C every bit rapidly as they absorb it, it is assumed, would non last as a species. Consequently, in rule, there exists an equilibrium between the degrees of C14 in the ambiance and that which exists in all life beings. When an being ceases to populate, it ceases besides to take in C14, and the rate of release ( radioactive decay ) can so be measured and compared to values refering to the half life of the isotope. At present, the best estimation for the half life of C14 is 5730! 40 old ages, therefore doing it an about ideal determiner to archeologists, and in peculiar archeologists concerned with diggings in the in-between east.Samples Because of the very nature of carbon 14 dating, the ideal sample pool is limited. Preferably the sample is organic in composing, and is free of any taint, such as exposure to other organic stuff that would skew the readings. This is peculiarly of import in footings of wadding and transporting the sample to a carbon 14 research lab. Below is a list of some possible samples and concerns for each. Charcoal and Wood are prevailing among samples found at archeological sites. Both are preferred because there is small opportunity of taint. However, the possibility of belowground H2O doing a alteration in C14 impregnation demands to be considered with the wood coal. And, while non considered taint per Se, precut growing in wood samples needs to besides be taken into history. For case, if the wood being sampled was cut from the centre of a tree, the day of the month read from the analysis would be the day of the month the tree started to turn, non the day of the month the tree was felled for usage in building. Most of the clip this would account for an mistake on the line of 100-200 old ages. However, it could potentially be greater than that sing the life span of some trees like the Bristle cone Pine is 4000+ old ages. & # 8220 ; Short-lived & # 8221 ; Samples include points such as seeds, fells, paper, fabric, grass, and grains. These are normally preferred to the wood samples because of the possible job of precut growing. They are called & # 8220 ; ephemeral & # 8221 ; due to the fact that they are, or are made from, points with a comparatively short life span. Like the wood and wood coal listed above, there is small opportunity of taint. Ivory is an first-class campaigner for dating because it is rare that the specimen will be contaminated. This is due to compression in its construction and the fact that it, for the most portion, remains in a province of saving comparable to that of modern-day samples. There have been ivories found over 40,000 old ages old that were foremost suspected to hold come from contemporary elephants. Like trees though, attention demands to be taken in determining where in the ivory the sample originated. Whereas in trees, the centre is the oldest, it is merely the antonym for ivories. Boness are frequently found at archeological sites, but they present a unique job for C dating. First, the C found in castanetss is largely inorganic and unsuitable for proving. Second, castanetss are really porous. Unless a good seal is established around the sample, it is really likely the sample will be contaminated by land H2O. This can throw a day of the month off well. The best castanetss to utilize so, are 1s that have been preserved within a heavy bed of coaling from a fire or volcanic activity. Collagen in castanetss can besides bring forth C, but to day of the month it has performed ill in set uping a dependable consequence. Pottery and Iron are non normally used as samples in C14 testing, but there are times when they can bring forth accurate day of the months. However, clayware must be contain at least 1 % organic C to hold with normal control samples. Other trials utilizing the same or even higher per centum, nevertheless, produced inconsistent consequences. Certain types of Fe can be used, but requires a high temperature furnace to burn the C in the Fe. Iron from meteors can non be used. As I have already alluded to above, transporting involves particular attention in how the sample is prepared, and what the sample is sent in. Below are stairss for consideration in acquiring a sample from the site of the excavation to the research lab for a successful day of the month. Collection of the sample to be analyzed is the first measure. Care should be taken non to pollute the sample with contact of human tegument or other organic stuffs. However, this is non ever a troublesome undertaking. Large pieces of wood covered with earthen stuff, and storages of grain and such can normally be dealt with with small fright of taint by human contact. Nevertheless, proper tools such as trowels, pincers, spades, and the similar should be present to cover with smaller points like pieces of wood coal embedded in soil. Particularly with the smaller samples, it is wise to divide them from as much of the earthen stuff as is possible to avoid farther dislocation and homogenisation during the transportation. And, as with all samples collected from a site, it is of import that some elaborate record be maintained of the carbon 14 sample? s stratigraphic context so that its readings might be cross-checked with other readings refering to a peculiar degree. Boxing the sample is comparatively easy, but the importance can non be overstated. The container one chooses truly depends on what organize the sample is in. If the sample is big and/or sufficiently solid, even cloth or paper will make. However, most samples necessitate something like the organically impersonal environment of plastic or metal, sealed with a strongly adhesive tape. If possible, samples should be dried before transporting to forestall the growing of mold. Finally, each container should be labeled on the exterior to guarantee proper designation. Contamination at this point needs to be better defined. There are many factors that may lend to a sample going contaminated. When stating & # 8220 ; contaminated, & # 8221 ; I am mentioning to the consequence of any procedure that causes a theoretically pure sample to go impure, and therefore bring forth a skewed reading. So far we have merely dealt with the human component. However, events such as atmospheric C14 fluctuations, natural alterations due to glaciation promotion or retreat, human activity, deep Marine effects, exposure to difficult H2O, and volcanic activity can all lend to a sample? s taint. Acknowledging these factors as potentially being present in the stratigraphic context of a discovery is important to obtaining an accurate date.Methods of Dating Solid-Carbon dating was the first method developed back in the early 1950? s by Libby and some of his pupils. It is no longer used to three drawbacks ass
ociated with it. First is self- soaking up. When its beta atom disintegrates, the energy degree produced by the dislocation is really low, and hard to observe. Thus it required a big sample to observe something more than a fraction of the decomposition. Second, C absorbs instead good. Many samples were contaminated due to the radioactive dust in the air from atomic trials in the 50? s. The samples could be cleaned, but non with the certainty needed for accurate readings. Last, the reaction rate of C dioxide varied when exposed to Mg during the process, possibly giving manner to a few day of the months that were clearly excessively old for the control sample. Gas-Counting was the method that replaced the solid-carbon method. This method was popular for a clip in the late 50? s, after which clip many research labs switched to utilizing relative numeration or scintillation numeration. Gas-counting fundamentally involves the rapid burning of a sample ( acidification in the instance of inorganics ) , and so many phases of chemical remotion of negatively charged and radioactive drosss. Then, because of the presence of Rn ( half life of 3.82 yearss ) , the sample is stored for two hebdomads until this dross has decayed below the bound of sensing. This can do the full procedure stretch out to every bit much as a month for a reading. Liquid Scintillation Techniques are besides used in some research labs. Though the chemical science involved is well more complicated, it normally achieves the same quality of consequences as obtained with the gas numeration method. However, there are two advantages to the scintillation procedure. One is that the equipment needed for numeration is more readily available than is for the gas numeration method. This is an of import cost factor because, while the gas numeration method requires much human intercession and processing, the equipment used for scintillation is normally semiautomatic, and hence utilizations less manpower. Second, there is a much greater flexibleness with the scintillation procedure. With the somersault of a switch, the research lab can alter from standardization to a reading for an unknown sample. Accelerator Mass Spectrometry is the latest technique being used to day of the month samples. Whereas the other three are based on detecting the decay merchandises of C14, AMS counts the figure of C14 atoms present comparative to the figure of C12 and C13 atoms in a peculiar sample. To make this, the AMS system was built on the engineering of the mass spectrometer. With the MS, a magnetic field is applied to a traveling charged atom, and the atom is deflected from the consecutive way along which it was going. If charged atoms of different mass, but the same speed, are capable to the same magnetic field, the heavier atoms are deflected the least. The AMS works likewise, nevertheless, the charged atoms are driven to really high velocities by big electromotive forces of electricity. This allows the minute degrees of C14 to be detected among the higher degrees of elements such as N14 and CH13. The AMS system has two major disadvantages. The first is the high building and care costs. Constructing the installation entirely can run every bit much as $ 2 million. The 2nd is the demand for strict pretreatments ( such as the remotion of Ca hydroxyapatite from bone, and cellulose from wood ) to maintain even infinitesimal degrees of taint from doing major mistakes in dating consequences. However, AMS is more efficient than the conventional methods for several grounds. 1 ) It can accurately day of the month a sample 1000 times smaller than can conventional techniques. This means smaller artefacts or specimens can be, for the most portion, preserved by the archaeologist alternatively of being destroyed in the dating procedure. 2 ) Other chemicals can be detected more easy in a sample. This allows the research lab to observe the effects of taint on the consequences. 3 ) With AMS a research lab can run every bit much as 1000 trials per twelvemonth because of the 2-3 hr proving clip. With conventional methods, it can take 1-3 days.Test Results Most of the contention and misconstruing environing carbon 14 dating revolves around the trial consequences indicating to a day of the month or day of the months that person does non hold with. As with all scientific methods, there are bounds to what radiocarbon dating can and can non make. Besides, there are inquiries refering mistakes, answerability, and a consistence of criterions to be considered. The Maximal age bound for conventional methods is about 40 000 old ages, whereas the bound for AMS is controlled by the single machine? s stableness and taint introduced or missed during the processing of little samples. As the sample gets older, degrees of C14 can drop to the point where it is hard to mensurate against the background degree of course present. When this is the instance, consequences are quoted as either “infinite” or “background.” The Minimum age bound for all methods is non less than 200 old ages. Consequences indicating to an age of less than 200 old ages are reported as “modern.” Contaminations here can happen due to the universe? s dodo fuel and atomic bomb activity, and consequences demoing more C14 than would usually be seen in modern-day samples have been quoted. Error is present in every scientific procedure. Normally, experimental mistake is calibrated by reiterating the measurement procedure. However, this is non really practical in carbon 14 dating due to the sample size, clip, and cost factors. The error term ( s ) , so, is estimated for each sample and applied as a known measuring. Traveling with the normal distribution curve, the true consequence is expected to hold a 68.3 % opportunity of being within 1s of the experimental consequence, a 95.4 % opportunity of being within 2s of the experimental consequence, and a 99.7 % opportunity of being within 3s of the experimental consequence. To day of the month there is no recognized convention as to merely how a research lab should use the mistake appraisal. All research labs include an appraisal based on Poisson statistics ( industry broad criterion based on known counts ) . But how those statistics are applied will differ from lab to lab. This is because, over a short clip period, the decay rate for C14 is non precisely predictable. However, the per centum of mistake can be reduced significantly by an addition in count clip in the conventional methods. Liquid Scintillation gives eight counts per minute per gm for a modern sample. To see a maximal mistake of 1 % ( an mistake term of about 80 old ages ) , a five gm sample would necessitate to be counted for approximately 250 proceedingss. The older the sample, the longer it takes to bring forth the same error term. Increasing the proceedingss of numeration, or the size of the sample will besides impact the result in the manner of a more accurate consequence. In add-on, several samples must be sent out to different research labs so that a “blind” and impartial consequence will be produced. Finally, truth and preciseness are frequently used interchangeably when talking in footings of mistake. However, they are rather different. Accuracy refers to systematic mistakes in relationship to a true consequence. There may or may non be preciseness associated with these consequences. Precision, on the other manus, refers to how tightly associated the consequences are with each other. It fundamentally measures the entropy of mistakes. These consequences may or may non be accurate in footings of the true consequences in this instance. Thus, an accurate consequence is more desirable than a precise consequence because of the relationship between it and the true consequence. If possible, though, both are pursued. Last, a statistical theoretical account will be applied to extinguish any utmost consequences before a trial consequence day of the month is settled upon.Calibration Radiocarbon dating plants really good when seeking to set up a wide estimation of age. The jobs start when seeking to set up calendar day of the months. This is where standardization, specifically that of dendrochronology, is most helpful. Dendrochronology, the establishing of calendar day of the months through the survey of tree rings, can graduate with great truth carbon 14 dating so that it can more expeditiously be used to set up specific ages and day of the months for the archeologist. Long chronologies can be plotted by get downing with life trees and overlapping them with older, felled trees. This procedure is continued as far back as possible. Through usage of trees like the Bristle Cone Pine, we now have chronologies dating back 8 000 old ages. Dating these findings by carbon 14 methods so gives us a statistical curve of standardization based on the comparing of absolute day of the months ( tree rings ) and approximative ages ( carbon 14 ) . Labs can so utilize this statistical theoretical account to account for any natural mistake inherent in the carbon 14 procedure.
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Graduate Paper written in Spring of 1998.Grade received: A9.5 pages plus bib.
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