To: All Nov-23-93 07:39PM Subject: Re: Shroud of Turin on EWTN last night Followup-To: sci

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To: All Nov-23-93 07:39PM Subject: Re: Shroud of Turin on EWTN last night Organization: NIST Electricity Div From: (Richard Steiner) Message-ID: Followup-To: sci.skeptic Newsgroups: sci.skeptic In article , (Bo Parker) wrote: > Greetings > > I watched the show "Focus" on the Eternal Word Television Network last > night (11/22/93). The show concerned the claims of (Dr.?) John Jackson and > his wife (Rebecca?), including their carbon-dating of the Shroud of Turin > to the time of Jesus. The Jacksons are from an organization called, I > believe, the Shroud Center of Colorado. > > The main point the Jacksons presented was that earlier carbon-dating which > placed the Shroud's origin in about the 15th century hadn't taken into > account the "fact" that the fire that partially burned the Shroud many > years ago (when?) had altered the C14/C12 ratio used in C dating, thus it > is necessary to apply the results of a Russian scientist (don't remember > the name) to "correct" the C dating results. When this correction is > applied, lo and behold, the Shroud dates to the time of Jesus. But > wouldn't the carbon from the burned cloth have the same C14/C12 ratio as > the unburned cloth? Someone also brought up the fact (?) that the Shroud > had been at least partially boiled in oil for some reason. Jackson said > that this would not affect the carbon dating at all. Any net.experts [tm] > on C dating have comments on this? > Rest of article deleted. Hoo boy, I pass, on the questions from the rest of the original article. As for the carbon dating issue, here's a stab at clarifying what C-dating is. I am not an "expert" on either of these topics, but I am familiar with them. Forgive me if the technical details are overkill, but better to read and then judge for yourself. In whatever a plant grows in any single year, be it flax leaves, cotton bolls, or tree rings, the carbon grown (carbon-dioxide photosynthesis) into just that material has exactly the same ratio of C14/C12 as the atmosphere for that year. Forever after and unaffected by ANYTHING short of relativistic time dilation, the ratio decreases exponentially via regular C14 radioactive decay, that is, half the C14 disappears every 5370 years. Parts like animal hair or skin that are constantly replenished or derive carbon from other animals will average the ratio over the lifetime of the part grower, which can complicate things but doesn't apply here. I don't remember whether the shroud cloth was linen(I think), cotton, or what; it doesn't make much difference. (Aside: Old methods counted the number of C14 decay products emmanating from a vaporized sample of large mass, while newer methods separate the isotopes in a mass spectrum analyzer using a very small mass sample. These new methods are what convinced the shroud keepers to allow the tests.) The big complication in C-dating arises because C14 formation takes place only in the upper atmosphere from hard radiation (a gamma ray changes an occasional N14 atom to C14) and is related to solar activity. Consequently, the ratio varies slightly over long time periods (many decades) and is measurable. Yet even this variability can be accounted for when recent items are dated. A curve plotting the ratio vs the year of origin has been derived from C-dated layers of tree rings that literally can be counted year by year as far back as about 10,000 years. With experimental error and the variability correction, the uncertainty for "recent" items is relatively small, i.e. on the order of 100 years or so, increasing drastically with ages beyond this correction curve. With regard to this particular case, I can think of three relevant possibilities that could have affected the carbon-dating uncertainty. One, the fabric in the tested threads was not representative of the main part of the cloth. But then again, single threads run continuously across an entire sheet, a spool of thread is usually made from fresh fibers harvested at the same time and place, and the testers chose threads which could not have been "added later" as a border. As I recall, different labs around the world each tested several samples from different shroud areas, including control samples not from the shroud. Every lab reported similar results. Two, if the cloth were chemically contaminated (boiled in vegetable oil? petroleum oil is too old to contain much C14.), then the measured age could be "more recent", since it would be the average of the new and old carbon, weighted according to the carbon mass of the two kinds of material. However, C12 and C14 are chemically identical, but oil and fiber have different chemical properties, so presumably, chemists could detect this and either find pure fibers or separate them while not affecting the ratio within either original fibers or contaminate. Three, exposure to certain kinds of radioactive emissions changed the ratio, as in, the picture effect itself. Heat or chemical changes from the fire would have no effect (charcoal remnants from prehistoric fires are good items for dating the fire users.) It would have taken a very unusual radiation, though, to have caused the picture in the middle, but altered only the carbon ratio at the edges, AND not physically damaged or made any other part of the shroud radioactive. To counter this and other arguments, I know they tested the pollen in dust taken from the cloth as an independent check on the C-dating technique. By comparing the pollen to existing samples from different places and times, a date of nearly the same era of around 1500 AD was found (I think), and may have even been from a different area of Europe (I'm not absolutely sure about this. I recall that the pollen interpretation was somewhat subjective, and one could argue that the pollen was trapped later, but where did the earlier pollen go?). Judge for yourself. Richard Steiner


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