A Review of Radio Carbon Dating, Potassium Argon Dating, Seriation and Stratigraphy

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Explain the importance of the following dating methods: (a) radio carbon dating, (b) potassium argon dating, (c) seriation, (d) stratigraphy.

Archaeology can be defined as “the scientific study of the human past, of ancient human behaviour, from the earliest times right up to the present.”(Fagan, 2006) .The study of archaeology as an academic discipline is dependant on the accuracy of various dating methods. Dating methods in archaeology can be divided into two groups: Relative dating methods and Absolute dating methods. Although the importance of the different dating methods may outweigh each other, the all are very important to the study of archaeology as a whole. This essay shall focus on the importance of radio carbon dating, potassium argon dating, seriation and stratigraphy to the archaeological study.

Accurate dating has always been of importance to scientist and archaeologist alike. In archaeology dating can be categorised into relative dating and absolute dating techniques. In moving forward explain the importance of radio carbon dating, potassium argon dating, seriation and stratigraphy to the archaeological study, one must first understand the difference between relative dating and absolute dating in archaeology. Relative dating in archaeology assumes the age of an artifact in relation and by comparison to other objects found in its environs. The style of the artifact and its archaeological location stratigraphically are required to arrive at a relative date. The limit to relative dating is that it cannot provide an accurate year or a specific date of use. Absolute dating on the other hand is the method of determining an approximate calculated age of an artifact in archaeology. The goal of archaeologist is ultimately to know how old sequences, sites and artefacts are in calendar years. To accomplish this absolute dating methods are used. From traditional historical methods to those which are based on the great variety of modern scientific techniques currently available. As compared to relative dating which only provides an order of events, absolute dating presents archaeologists with a more calculated evaluation of the object’s age.

The first area of discussion in understanding the different dating techniques in archaeology would be stratigraphy. According to Renfrew and Bahn, “stratigraphy is the study of stratification- the laying down or depositing of strata one above the other.” (Renfrew and Bahn 2008, 122). This basically involves ordering things into sequences. A succession of layers should provide a relative chronological sequence from the earliest (the bottom layer) to the latest (top), as seen in figure one. It’s important to note that stratigraphy involves the Law of Superposition. Fagan describes the Law of Superposition as, “the notion that underlying levels are earlier than those that cover them.” (Fagan 2009, 103). He further explains that the lower levels are relatively earlier than the later strata, which is basically entails. Scientific archaeologists grasped at this rather quickly, although it wasn't used as a consistent technique until around the turn of the nineteenth century. Since then, the technique has been refined, and tools such as theHarris Matrixassist in picking out the sometimes quite complicated and delicate deposits. The study of stratigraphy on archaeological sites was used in North America and Mesopotamia. The importance of stratigraphy is good and well but it still does not provide an accurate form of dating, it all involves speculation. This is since as a downfall since archaeological research strives in the most accurate form of understanding of the past societies and cultures. ""

Figure1

Title: Stratification example

Source: pages.vassar.edu

The other archaeological dating method to be discussed is seriation. Seriation is a very common form of archaeological interpretation. Seriation is a form of relative dating technique. With the assumption that artefacts changed with passing time in radical ways, archaeologist use seriation techniques to place artefacts in chronological order. Seriation is the changing of style of an object over time. Renfrew and Bahn explain that there are two versions of the seriation technique: contextual seriation and frequency seriation. Contextual seriation, also called sequenced dating is where artefacts are arranged according to the frequencies of their co- occurrence in specific context. In the nineteenth century Sir Flinders Petrie was the founding father of this type of seriation. He used this method to establish order in large Egyptian graves. Frequency seriation on the other hand, was established by an American archaeologist at a Mayan site in Yucatan 1940. The principle of frequency seriation relies predominantly on measuring changes in the proportional abundance, or frequency of a ceramic style. W.S. Robinson and G.W. Brainerd in their paper published in American Antiquity in 1951 hypostasised two statements about frequency seriation. “First, the assumed that pottery styles gradually become more popular, reach peak of popularity, and then fade away. Secondly, they argued that a given time period, a pot style popular at one site would similarly be popular at another.”(Renfrew and Bahn 2008, 128). Archaeologist such as James A. Ford working in American Southeast and Frank Hole in Iran were able to establish chronological validity using this method. “Nevertheless it should always be borne in mind that seriation by itself does not tell us which end of a given sequence is first and which last- the true chronology has to be determined by other means.”(Renfrew and Bahn 2008, 128).

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Figure2

Title: Seriation of Pottery

Source: http://anthro.palomar.edu/time/glossary.htm

The next dating method to be discussed is potassium argon dating. This is a type of absolute dating technique. This method is used mainly to date rocks thousands of years old. “Geologists use this method to date rocks as early as four to five billion years old and as recent as 100,000 years old before present.” (Fagan 2009, 119). The earth’s crust is engulfed with potassium and as a result it is present in almost every mineral. Potassium argon dating is based on the principle of radio active decay, the steady but very slow decay of radioactive isotope potassium -40 (40K) to the inert gas argon-40 (40Ar) in volcanic rock. Knowing the decay rate of 40K-its half life is around 1.3 billion years- a measure of the quality of 40 Ar trapped within a 10g rock sample gives and estimate of the date of the rock’s formation. The major limitations of the technique are that it can only be used to date sites buried by volcanic rock, and an accuracy of +10 percent is rarely achieved. However, potassium argon dating played a crucial role in the site Olduvai Gorge in Tanzania. The site in East Africa was the basis of the study of human evolution, as it yielded fossil remains of Australopithecus, Homo habilis, and Homo erectus, as well as large numbers of stone artifacts and bones. It should be noted that the Rift Valley in Olduvai is a volcanic area, and its two million year old chronology has been established by potassium argon dating of the relevant deposits of harden volcanic ash and other materials.

The final archaeological dating method to be discussed is the absolute dating technique radio carbon dating. Radio carbon dating has a major impact on archaeology, in particular on pre history since the lack of a written record leaves much to conjecture. Radio carbon has transformed our understanding of the past. According to Bowman the materials which can be dated by radio carbon are those which once formed part of the biosphere and are therefore organic. For example, the most commonly preserved sample types occurring on British sites are bones, shells and charcoal. (Bowman 1990, 12). The pioneer for radio carbon dating is the American chemist Willard Libby, who in 1949 published the first radio carbon dates. Libby had been one of the scientists during World War II who was studying cosmic radiation, the sub- atomic particles that constantly bombarded the earth, producing high- energy neutrons. “These neutrons react with nitrogen atoms in the atmosphere to produce atoms of carbon-14 (14C), or radio carbon, which are unstable because they have eight neutrons in the nucleus because they have eight neutrons in the nucleus instead of the usual six as for ordinary carbon (12C). This availability leads to radioactive decay of 14C at a regular rate. Libby estimated that it took 5568 years of half of the 14C in any sample to decay – its half life – although modern research indicates that more accurate figure is 5730 years.” (Renfrew and Bahn 2008, 142).

Libby analyzed that the decay of radiocarbon at a constant rate should be balanced by its constant production through cosmic radiation and therefore the proportion of 14C in the atmosphere should remain the same throughout time. However, Libby’s about the level of 14C in the atmosphere has varied some what, since the radio carbon dates obtained from tree- rings show that before about 1000BC, trees were exposed to greater concentrations of atmospheric 14C than they are today. At this point it should be noted that this radio carbon method can be used anywhere, no matter the climate, as long as there is material or organic origin. This is different as compared to the other absolute dating technique discussed above potassium argon which is only limited to dating volcanic rocks. During the latter half of the twentieth century, certain advancements had been made to help correct the limitations of radiocarbon dating. For instance the accelerator mass spectrometry (AMS) method is becoming the dominant method used in radiocarbon dating. This requires smaller samples still. AMS counts the atoms of 14C directly, disregarding their radioactivity. The minimum sample size is reduced to as such little as 5-10mg, thus enabling precious organic materials such as the Turin shroud , to be sampled and directly dated, and making feasible the direct dating of pollen. Primarily, it was hoped that the dateable time span for radiocarbon using AMS could be pushed back from 50,000 to 80,000 years, although this is proving difficult to achieve in part because of sample contamination. (Thomas 1999, 76). It should be noted that for inorganic materials, thermoluminesence and other new dating techniques are useful.

As compared to the other dating techniques as discussed above, radiocarbon dating can be seen as the most accurate and important to archaeologist in putting together the past. It was used to date Upper Paleolithic paintings in the Chauvet Cave, southern France. However all results over 30,000 BP are subjected to problems. Radiocarbon was also used to assert to validity of the chronology of Europe. In the Caribbean, overseas radio carbon dating techniques are also used, in particular Trinidad. The nation’s parliamentary building currently is undergoing excavations, and the materials they find are shipped overseas for accurate dating using radiocarbon because Trinidad does not have the proper equipment for dating it, since radiocarbon equipment maybe some what expensive for a development nation to endure.

In conclusion it can be said that radio carbon dating, potassium argon, seriation and stratigraphy are important dating techniques one way or the other. Although radiocarbon can be seen as the most efficient because of it accuracy and how far back it can date, the other dating techniques are very much relevant

BIBLIOGRAPHY

BOOKS

Bowman Sheridan, Interpreting the Past. Radiocarbon Dating. Los Angeles: University of California Press, 1990, Print.

Courbin Paul, What is Archaeology? An essay on the Nature of Archaeological Research. United States of America: The University of Chicago Press, 1988. Print

Fagan Brian, Archaeology. A Brief Introduction. New Jersey: Pearson Education, 2006, Print.

Renfrew Colin and Bahn Paul, Archaeology: Theories, Methods, and Practice. United States of America: Thames and Hudson Ltd, 2008, Print.

Thomas Hurst David, Archaeology Down to Earth. United States of America: Harcourt Brace College Publishers, 1999, Print.

WEBSITES

Swaminathan, Nikhil. “Nondestructive Radiocarbon Dating - College Station, Texas”. Archaeology Archive. A publication of the Archaeological Institute of America, accessed October 30th 2014. http://archive.archaeology.org/1101/topten/texas.html.

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