Introduction Essays (3116 words) - Isotopes Of Carbon, Radioactivity

Introduction The discipline of archaeology can open up the past to us in a way in which we can enter into a dialogue with our ancestors. There are many ways it can do this: stratigraphic excavation, pottery typology, socio-historic interpretation, etc. However, one thread running through this increasingly focused pursuit is that of dating the physical findings to a particular cultural timeline. This is crucial if we are to know, with as much certainty as is allowed, who we are speaking with. Indeed, dating may be the proverbial thread that holds entire pursuit together, without which the individual pieces of the puzzle might be compared to the children of Israel, who the author of Judges describes as each going off in their own direction. Like the king Judges so wistfully imagines, dating brings cohesiveness and direction to a potentially (or real?) chaotic situation. In this paper I will explore the particulars of radiocarbon dating; from its background and origin, to discussion of samples, method, results, and calibration. Background With the explosions of the first atomic bombs echoing in his thoughts, Willard F. Libby, working with A.V. Grosse, Ernest Anderson, and several students, pioneered the work on a theory that natural C14 not only existed, but that it could also be used as a method for dating certain artifacts of antiquity. Working under the premise of his 1946 paper that suggested C14 might exist in all living organisms, a team including Libby and Grosse collected readings from the Baltimore sewer system. It was discovered that methane collected from these sewers contained radiocarbon activity, whereas methane derived from petroleum did not. These findings gave strength to the theory suggested in his paper, but several years of additional research were needed. After their sewer experiments, global samples of wood were gathered in which the researchers discovered a consistent level of radiocarbon deposits. From that point on, the theory developed until it became widely accepted within the scientific com munity, culminating with Libby's acceptance of the Nobel prize for chemistry in 1960. The Origin of C14 Natural C14 is formed in the upper atmosphere when nitrogen reacts with neutrons. Neutrons are produced by cosmic rays bombarding the earth, and are thus dependent upon the level of cosmic ray bombardment, as well as the earth's natural ability to receive the rays from space. The only known deterrent to cosmic ray absorption is the earth's magnetic field. The stronger it is, the less the cosmic rays reach the earth. Once the C14 is produced, it exists in a very small quantity in carbon dioxide, a product of oxygen and carbon. From here, all living organisms take in C14 by either photosynthesis (plant life) or the food chain (breathing life). Since C14 is radioactive, and therefore destructive to life, it is necessary for all organisms to release C14 at basically the same rate they consume it. Those that do not release radioactive carbon as quickly as they absorb it, it is assumed, would not survive as a species. Consequently, in principle, there exists an equilibrium between the leve ls of C14 in the atmosphere and that which exists in all living organisms. When an organism ceases to live, it ceases also to take in C14, and the rate of release (radioactive decay) can then be measured and compared to values pertaining to the half-life of the isotope. At present, the best estimate for the half life of C14 is 5730! 40 years, thus making it an almost ideal determinant to archaeologists, and in particular archaeologists concerned with excavations in the middle east. Samples Because of the very nature of radiocarbon dating, the ideal sample pool is limited. Preferably the sample is organic in composition, and is free of any contamination, such as exposure to other organic material that would skew the readings. This is particularly important in terms of packing and shipping the sample to a radiocarbon laboratory. Below is a list of some potential samples and concerns for each. Charcoal and Wood are predominant among samples found at archaeological sites. Both are preferred because there is little chance of contamination. However, the possibility of underground water causing a change in C14 saturation needs to be considered with the charcoal. And, while not considered contamination per se, precut growth