gordon@uw-june (Gordon Davisson) (08/01/85)
>>> [Ron Kukuk] On the >>> other hand, measurements made at hundreds of sites >>> worldwide [a,b] indicate that the concentration of >>> radiocarbon in the atmosphere rose quite rapidly at some >>> time prior to 3,500 years ago. If this happened, the >>> maximum possible radiocarbon age obtainable with the >>> standard techniques (approximately 50,000 years) could >>> easily correspond to a TRUE age of 5,000 years. >> [Gordon Davisson] >> Wrong! If there used to be more C14 in the atmosphere than there is now, >> it would make radiocarbon dates come out too *young*, not too old. At >> least try to get the direction of the error right! > [Lief Sorensen] > Would you please read that again, Gordon? HE DID NOT STATE THAT THERE USED > TO BE MORE C14 IN THE ATMOSPHERE THAN THERE IS NOW! On the contrary, he > stated that the amount of C14 in the atmosphere has increased sometime > during the last 3-4 thousand years. You are the one in error! Having reread Kukuk's words, I realize that it can be parsed either way. So which did he mean? I don't have access to either of his references (one was unpublished, the other from a creationist journal), so I had to find my own reference. The one I picked was "Radiocarbon Dating," edited by Rainer Berger and Hans E. Suess, published by the University of California Press, 1979. The appendix and several of the articles give plots of C-14 dates versus dendrochronological (tree-ring) dates indicating that earlier than about 0 BC, carbon dates tend to be *too young* (as I said earlier). In fact, a true date of 5,000 BC corresponds to a carbon date around 4,000 BC, not 50,000 BC as Kukuk suggested. Either Kukuk's facts or his logic are in error. -- Human: Gordon Davisson ARPA: gordon@uw-june.ARPA
lief@hpfcla.UUCP (08/13/85)
> [Gordon Davisson] > ...The one I picked was "Radiocarbon Dating," edited >by Rainer Berger and Hans E. Suess, published by the University of >California Press, 1979. The appendix and several of the articles give >plots of C-14 dates versus dendrochronological (tree-ring) dates >indicating that earlier than about 0 BC, carbon dates tend to be *too >young* (as I said earlier). In fact, a true date of 5,000 BC corresponds >to a carbon date around 4,000 BC, not 50,000 BC as Kukuk suggested. >Either Kukuk's facts or his logic are in error. How about Stuart Piggott's report (a British archaeologist) in "The Radio-Carbon Date from Durrington Walls", ANTIQUITY, xxxiii, No. 132, (Dec. 1959), page 289. Here he reports that two radiocarbon tests on a sample of charcoal indicated a date of 2620-2630 BC for an ancient structure at Durrington Walls in England. However, absolutely compelling archaeological evidences called for a date approximately 1000 years later. Another prominent archaeologist, Professor V. Milojcic, states that some radio carbon dates from south-eastern Europe are 1000 years too high -- see H.T. Waterbolk, "The 1959 Carbon-14 Symposium at Groningen," ANTIQUITY, xxxiv, No. 133, (Mar 1960), pages 14-18. Unless Carbon-14 dating techniques have changes dramatically since 1959 I would be inclined to be skeptical about any carbon-14 dates! The fact that it can be 1000 years off for something as recent as 1600 BC suggests to me that Carbon-14 dating is worthless, and any scientist who uses it cannot be taken seriously. If I'm not mistaken, it is rarely used anymore. However, the interesting thing is that many people are still clinging tightly to the data gathered back in the days when Carbon-14 dating was in vogue -- worthless data! Lief Sorensen HP Fort Collins, CO Uucp ...!hpfcla!lief
bill@utastro.UUCP (William H. Jefferys) (08/24/85)
> How about Stuart Piggott's report (a British archaeologist) in > "The Radio-Carbon Date from Durrington Walls", ANTIQUITY, xxxiii, No. 132, > (Dec. 1959), page 289. Here he reports that two radiocarbon tests on a sample > of charcoal indicated a date of 2620-2630 BC for an ancient structure at > Durrington Walls in England. However, absolutely compelling archaeological > evidences called for a date approximately 1000 years later. Another prominent > archaeologist, Professor V. Milojcic, states that some radio carbon dates > from south-eastern Europe are 1000 years too high -- see H.T. Waterbolk, > "The 1959 Carbon-14 Symposium at Groningen," ANTIQUITY, xxxiv, No. 133, > (Mar 1960), pages 14-18. > > Unless Carbon-14 dating techniques have changes dramatically since 1959 > I would be inclined to be skeptical about any carbon-14 dates! The fact that > it can be 1000 years off for something as recent as 1600 BC suggests to me > that Carbon-14 dating is worthless, and any scientist who uses it cannot > be taken seriously. If I'm not mistaken, it is rarely used anymore. > > However, the interesting thing is that many people are still clinging > tightly to the data gathered back in the days when Carbon-14 dating was in > vogue -- worthless data! You are out of date by 25 years. The radiocarbon dates of such artifacts as Stonehenge (I cannot speak to Durrington Walls) were older than the archaeological dates by about the amount you quote, but other evidence has since confirmed the radiocarbon dates. The "compelling archaeological evidence" that caused archaeologists to date Stonehenge, for example, too young, turned out to be preconceived notions about its being too sophisticated for the inhabitants of Britain of the time to have built without outside influence. Assumptions were made about influences from other cultures that have turned out to be wrong. In addition, Stonhenge was not built at once, but over a period of several centuries. Thus there can be significant variations in dates of Stonehenge artifacts, even using reliable techniques. Similar comments may also apply to Durrington Walls. Since 1960, calibration of the radiocarbon dating system by use of tree ring data has considerably strengthened it. Other techniques have also become important, but radiocarbon dating remains an extremely valuable tool, whose dates can now be corroborated by other means. The bottom line is that we are in much better shape, and can rely on physical dating methods with much more confidence, than was possible in 1960. -- "Men never do evil so cheerfully and so completely as when they do so from religious conviction." -- Blaise Pascal Bill Jefferys 8-% Astronomy Dept, University of Texas, Austin TX 78712 (USnail) {allegra,ihnp4}!{ut-sally,noao}!utastro!bill (uucp) bill%utastro.UTEXAS@ut-sally.ARPA (ARPANET)
pamp@bcsaic.UUCP (pam pincha) (08/27/85)
In article <14600041@hpfcrs.UUCP> lief@hpfcla.UUCP writes: > > > Unless Carbon-14 dating techniques have changes dramatically since 1959 >I would be inclined to be skeptical about any carbon-14 dates! Yep it has. The technique between now and then has changed drastically. The collection techniques,preparation techniques and analysis have gotten dramatically better. What has been determined is that there are certian conditions that can contaminate a specimen. Regional differences can also play a factor in the dates determined. STILL,within the limitations and with reasonable precautions this technique is quite usefull AND IS STILL BEING USED. It's just that its limitations are much betterknown and more care is taken before results are bandied about. ----------------------------------------------------------------- P.M.Pincha-Wagener (bcsaic!pamp) (usual disclaimer) ----------------------------------------------------------------
michaelm@3comvax.UUCP (Michael McNeil) (08/28/85)
> >... indicating that earlier than about 0 BC, carbon dates tend to be *too > >young* (as I said earlier). In fact, a true date of 5,000 BC corresponds > >... > > ... of charcoal indicated a date of 2620-2630 BC for an ancient structure at > Durrington Walls in England. However, absolutely compelling archaeological > evidences called for a date approximately 1000 years later. Another > archaeologist, Professor V. Milojcic, states that some radio carbon dates > from south-eastern Europe are 1000 years too high ... > > Unless Carbon-14 dating techniques have changes dramatically since 1959 > I would be inclined to be skeptical about any carbon-14 dates! The fact that > it can be 1000 years off for something as recent as 1600 BC suggests to me > that Carbon-14 dating is worthless, and any scientist who uses it cannot > be taken seriously. If I'm not mistaken, it is rarely used anymore. > > However, the interesting thing is that many people are still clinging > tightly to the data gathered back in the days when Carbon-14 dating was in > vogue -- worthless data! Well, Carbon-14 dating *has* changed dramatically since 1959! I never cease to be amazed at how old data and theories are tossed around as the latest scientific word in this group. (One recent article referred to a scientific paper from *1907* for its anti-evolutionist arguments!) Sorry to have to clue you in like this, but science is *not* a subject based on ``truths'' revealed far in the past, to be unquestioned ever after. Science is a process of continual change and growth. Always there is error, but steadily the weight of evidence reveals errors, and these are weeded out in an evolutionary process of its own. Carbon-14 dating in its early days did incorporate an error, which caused many datings to be off by values such as has been described. This was due to the over-simplistic assumption that Carbon-14 was created in the upper atmosphere (by cosmic rays) at a constant rate over the last few tens of thousands of years (I yawn at any flames that all but the last of these didn't exist). This mistaken assumption was recognized due to the archeological inconsistencies. The dating errors were made precise as a result of the advance in tree ring dating techniques which has occurred in the last couple of decades. Tree ring studies have allowed Carbon-14 dating to be recalibrated on the basis of exactly what the Carbon-14 deposition rate was during each temporal period. For those who are not familiar with the science of tree ring dating, every tree records a unique record of the climatic changes that have occurred during its lifetime. The width of each ring tells how well the tree did that year, and that in turn reflects the water, sunlight, and weather that it experienced. Year after year the rings record the climate, the changes in which form a pattern in the tree rings as unique as a fingerprint. The tree ring scientists started with living trees, and charted the story of the climatic changes that they told. Then, using wood from trees no longer living but whose ages were generally known, climatic ``fingerprints'' were located which matched those on living trees. Matching patterns proved that these trees were alive when living trees were alive. Their rings, however, often extended even further in the past than those of any trees now living, and from them the chart of climate ``fingerprints'' could be extended further back. Ever older wood samples were cross-correlated with the climatic record, and the climatic record extended ever further into the past. By this technique, not only have the climatic changes for many thousands of years been mapped, but the Carbon-14 technique has been calibrated and made precise. Far from being ``worthless,'' Carbon-14 dating is more useful and powerful than ever. Many contributing to this group seem to think that Carbon-14 and other scientific dating techniques are accepted blindly. This is not so. Every dating method is carefully checked wherever and whenever possible against dates derived by other techniques. Only when a dating technique stands the test of time, and data from different methods reinforces rather than conflicts with it, is it generally accepted. However, when a useful method *is* found to be flawed, it usually isn't just tossed away -- instead, if possible the problem is fixed! Michael McNeil 3Com Corporation ..!ucbvax!hplabs!oliveb!3comvax!michaelm
michaelm@3comvax.UUCP (Michael McNeil) (09/27/85)
[Oh, *please* don't eat me, Brer Line Eater Monster, Sir!] Reference: article <180@3comvax.UUCP> > Pray tell, then, how we can trust things like U-235 or U-238 since we > don't have any supporting evidence to test it against? > > If C-14 can be off by so much, so can methods that supposedly date > things much older. One should note well the studies (Michigan State, I > believe) which found major differences in dates provided by different > long-term (e.g., K-Ar, Rb-Sr, U-Pb, Th-Pb) methods. > > Larry Bickford, {amd,sun,decwrl,idi,ittvax,cbosgd}!qubix!lab Thanks for writing, Larry. Sorry to be long in answering, but I had intended to take more time researching my reply, with the thought of posting it for others who might also be interested. Unfortunately, I don't have time to do it well right now, so I'll reply briefly. The original article discussed carbon-14 dating rather than other, longer-term radioactive dating methods, but I grant you that the question of the one method leads quite naturally to the others. There is an important qualification which it's necessary to keep in mind when discussing variances in C-14 deposition over time. The rate of *decay* of carbon-14 does not vary, rather the rate of the *creation* of C-14 changes as the flux of cosmic rays changes. Once created, carbon-14 -- and all other radioactive isotopes -- decay at a constant rate. (Radioactive decay stems from the "weak" nuclear force, which so far as is known, is affected by practically nothing.) Unlike carbon-14, the other radioactive isotopes such as uranium and radium all derive, with the exception of a trifling amount of matter which arrived on meteorites, from the origin of the Earth. Either elements are left over from the beginning, such as uranium and thorium are, or the element is derived from the decay of other radioactive elements, such as is the case for radium, tritium, etc. Uranium is a particularly good candidate for dating with, since due to its long half-life, much uranium still exists on the Earth. Also, uranium-235 and uranium-238 are naturally mixed in constant proportions on Earth, so they provide a check against each other. When this is done, the results generally check out consistently. Comparing uranium-derived dates with dates found using other radioactive elements also generally cross-checks consistently. In addition, radioactive dating is continually checked against other, non-radioactive dating methods, such as the fossil and geologic record. These records in a way are quite similar to tree-ring dating. Like the tree rings, sequences of datable events are interspersed with the events of interest. The "tree rings" in this case are the alternating sequences of lava flows and sediment layers found all over the world. The lava flows contain the radioactive materials, trapped in their exact proportions as of the time the lava cooled. The sediments contain fossils, which identify the epoch when the sediments were deposited. When it is the radioactive clock that is being calibrated, known fossils provide dating which calibrates the degree of radioactive decay which has occurred. Then, when the radioactive-decay clock is properly calibrated, unknown fossils located in other sediments can be dated using it. Finally, to show that rates of radioactive decay *have* remained constant over time, several years ago a *natural reactor* was discovered in Africa. Geologically dated to a period several billions of years ago, the reactor -- a bed of uranium ore -- went critical, heated up, and quietly melted down a number of times over a long interval. Now, no uranium ore *can* approach critical nowadays, since uranium-238 can't fission normally, and the proportion of fissionable uranium-235 is too low in uranium today. No, the reason that the ore could go critical back then is simply due to the relative decay rates of U-235 and U-238 -- the shorter half-life of U-235 resulted in a higher proportion of U-235 to U-238 in that epoch. As for the Michigan State study you mentioned, I'm not familiar with it. It's a frequent occurrence on the frontiers of science, however, for preliminary results to be ambiguous or at variance with other researchers' results, only for the problem to be resolved later with better equipment and experiments. I suspect that's what has happened here. I assure you that scientists cannot forever ignore *genuinely* contradictory evidence -- too many of their colleagues would *love* to catch them at it! However, if you would like to forward me more information about the Michigan study you mentioned, I'll attempt to evaluate it. -- Michael McNeil 3Com Corporation "All disclaimers including this one apply" (415) 960-9367 ..!ucbvax!hplabs!oliveb!3comvax!michaelm Who knows for certain? Who shall here declare it? Whence was it born, whence came creation? The gods are later than this world's formation; Who then can know the origins of the world? None knows whence creation arose; And whether he has or has not made it; He who surveys it from the lofty skies, Only he knows -- or perhaps he knows not. *The Rig Veda*, X. 129