Radiocarbon dating considerations - Wikipedia
Specifically, there are two types of carbon found in organic materials: carbon 12 ( C) and carbon 14 (C). It is imperative to remember that. Measuring the difference in the radio between carbon and carbon is useful for dating the age of organic matter since a living organism is. When animals and plants are alive they take both ordinary carbon (C12) and radioactive carbon (C14) into their body through their food and.
We stick the garden hose in and turn it on full blast. The water coming out of the hose is analogous to the continuous production of carbon atoms in the upper atmosphere. The barrel represents the earth's atmosphere in which the carbon accumulates. The water leaking out the sides of the barrel represents the loss mainly by radioactive decay of the atmosphere's supply of carbon Now, the fuller that barrel gets the more water is going to leak out the thoroughly perforated sides, just as more carbon will decay if you have more of it around.
Finally, when the water reaches a certain level in the barrel, the amount of water going into the barrel is equal to the amount leaking out the perforated sides. We say that the input and output of water is in equilibrium.
The water level just sits there even though the hose is going full blast. The barrel is made deep enough so that we don't have to worry about water overflowing the rim.
Henry Morris argued that if we started filling up our empty barrel it would take 30, years to reach the equilibrium point. Thus, he concluded, if our Earth were older than 30, years the incoming water should just equal the water leaking out. That is, the equilibrium point should have long since been reached given the present rate of carbon production and the old age of the earth.
The next step in Henry Morris' argument was to show that the water level in our barrel analogy was not in equilibrium, that considerably more water was coming in than leaking out.
Explainer: what is radiocarbon dating and how does it work?
To that end, he quoted some authorities, including Richard Lingenfelter. Having accomplished that, Morris concluded that the barrel was still in the process of being filled up and that, given the present rate of water coming in and leaking out, the filling process began only 10, years ago.
It's a great argument except for one, little thing. The water is not coming out of the hose at a steady rate as our model assumed! Sometimes it slows down to a trickle so that much more water is leaking out the barrel than is coming in; sometimes it goes full blast so that a lot more water is coming into the barrel than is leaking out.
Thus, the mere fact that the present rate of water coming in exceeds that of the water leaking out cannot be extrapolated back to a starting time. And, that destroys the entire argument.
Figure 1 Lingenfelter's paper was written inbefore the cycles of C variation we described had been fully documented. The point is that fluctuations in the rate of C production mean that at times the production rate will exceed the decay rate, while at other times the decay rate will be the larger.
Strahler,p. Henry Morris chose not to mention that portion of the paper!Why Carbon Dating Might Be in Danger
Creationists don't want their readers to be distracted with problems like that -- unless the cat is already out of the bag and something has to be said. Tree-ring dating see Topic 27 gives us a wonderful check on the radiocarbon dating method for the last years.
That is, we can use carbon dating on a given tree-ring the year sequence having been assembled from the overlapping tree-ring patterns of living and dead trees and compare the resulting age with the tree-ring date. A study of the deviations from the accurate tree-ring dating sequence shows that the earth's magnetic field has an important effect on carbon production.
When the dipole moment is strong, carbon production is suppressed below normal; when it is weak, carbon production is boosted above normal. What the magnetic field does is to partially shield the earth from cosmic rays which produce carbon high in the atmosphere.
Contrary to creationist Barnes' totally discredited claims, which I've covered in Topic 11the earth's magnetic field dipole moment has, indeed, increased and decreased over time. Strahler presents a graph of the earth's dipole moment going back years. The curve is roughly fitted to mean values determined about every to 1, years The curve is roughly degrees out of phase with the C curve.
Bucha, who has been able to determine, using samples of baked clay from archeological sites, what the intensity of the earth's magnetic field was at the time in question.
Even before the tree-ring calibration data were available to them, he and the archeologist, Evzen Neustupny, were able to suggest how much this would affect the radiocarbon dates. Therefore, as already noted, Dr. Hovind's claim that carbon has been slowly building up towards a 30, year equilibrium is worthless. You now have the technical reason for the failure of Morris' model.
It may interest the reader to know that within this year period, where the radiocarbon method can be checked by tree-ring data, objects older than BC receive a carbon date which makes them appear younger than they really are! An uncorrected carbon date of years for an object would actually mean that the object was years old.
Seven hundred years or so is about as far as the carbon method strays from tree-ring dating on the average. Individual dates given on a correlation chart Bailey,p.
Carbon - Wikipedia
As it turns out, we have a check on the carbon production which goes back even further than years: Evidence of past history of C concentration in the atmosphere is now available through the past 22, years, using ages of lake sediments in which organic carbon compounds are preserved. Reporting before a conference on past climates, Professor Minze Stuiver of the University of Washington found that magnetic ages of the lake sediments remained within years of the radiocarbon ages throughout the entire period.
He reported that the concentration of C in the atmosphere during that long interval did not vary by more than 10 percent Stuiver,p. Thus, the available evidence is sufficient to validate the radiocarbon method of age determination with an error of about 10 percent for twice as long a period as the creation scenario calls for.
The dipole moment of the earth's magnetic field, sunspot activity, the Suess effect, possible nearby supernova explosions, and even ocean absorption can have some effect on the carbon concentration. However, these factors don't affect the radiocarbon dates by more than about percent, judging from the above studies.
Of course, when we reach the upper limit of the method, around 40, years for the standard techniques, we should allow for much greater uncertainty as the small amounts of C remaining are much harder to measure. Tree-ring data gives us a precise correction table for carbon dates as far back as 8, years. The above study by Stuiver shows that the C fluctuations in the atmosphere were quite reasonable as far back as 22, years ago.
The earth's magnetic field seems to have the greatest effect on C production, and there is no reason to believe that its strength was greatly different even 40, years ago. For a refutation of Barnes' argument see Topic Therefore, atmospheric variation in C production is not a serious problem for the carbon method. The evidence refutes Dr. Hovind's claim that the C content of our atmosphere is in the middle of a 30,year buildup.
Thus, we can dismiss this young-earth argument. The C decay rate is not constant. Several factors, including the year sunspot cycle, affects its rate of decay. It is painfully obvious that Dr. Hovind knows next to nothing about carbon dating! Changes in the sunspot cycle do have a noticeable, short-term effect on the rate of C production inasmuch as sunspots are associated with solar flares, which produce magnetic storms on Earth, and the condition of the earth's magnetic field does affect the number of cosmic rays reaching the earth's upper atmosphere.
Carbon is produced by energetic collisions between cosmic rays and molecules of nitrogen in the upper atmosphere. Sunspots have absolutely nothing to do with the rate of C decay, which defines the half-life of that radioactive element. Hovind has confused two completely different concepts. Quantum mechanics, that stout pillar of modern physics, which has been verified in so many different ways that I couldn't begin to list them all even if I had them at hand, gives us no theoretical reason for believing that the C rate of decay has changed or can be significantly affected by any reasonable process.
We also have direct observation: That radiocarbon ages agree so closely with tree-ring counts over at least years, when the observed magnetic effect upon the production rate of C is taken into account, suggests that the decay constant itself can be assumed to be reliable.
We also have laboratory studies which support the constancy of all the decay rates used in radiometric dating. A great many experiments have been done in attempts to change radioactive decay rates, but these experiments have invariably failed to produce any significant changes. It has been found, for example, that decay constants are the same at a temperature of degrees C or at a temperature of degrees C and are the same in a vacuum or under a pressure of several thousand atmospheres.
Measurements of decay rates under differing gravitational and magnetic fields also have yielded negative results. Although changes in alpha and beta decay rates are theoretically possible, theory also predicts that such changes would be very small [ Emery, ] and thus would not affect dating methods. There is a fourth type of decay that can be affected by physical and chemical conditions, though only very slightly.
This type of decay is electron capture e. Because this type of decay involves a particle outside the nucleus, the decay rate may be affected by variations in the electron density near the nucleus of the atom.
For example, the decay constant of Be-7 in different beryllium chemical compounds varies by as much as 0.
The only isotope of geologic interest that undergoes e. Measurements of the decay rate of K in different substances under various conditions indicate that variations in the chemical and physical environment have no detectable effect on its e. Dalrymple,p. Harold Slusher, a prominent member of the Institute for Creation Research, claimed that "Experiments have shown that the decay rates of cesium and iron 57 vary, hence there may be similar variations in other radioactive decay rates. This statement merely reveals Slusher's ignorance of nuclear physics.
Gamma decay of an excited state of iron 57 has been studied, but this has nothing to do with the kinds of decays used in radiometric dating. Brush,p. These changes are irrelevant to radiometric dating methods. They will switch tracks faster than you can say "tiddlywinks.
Morris claimed that free neutrons might change the decay rates. However, Henry Morris, that icon of creationism, only demonstrated that he knew no more about radiometric dating than does Dr. Free neutrons might change one element into another, but the decay rates all remain true to their elements.
How Accurate is Carbon Dating?
Another attempt by Morris invokes neutrinos. Morris [ ] also suggests that neutrinos might change decay rates, citing a column by Jueneman 72 in Industrial Research. The subtitle of Jueneman's columns, which appear regularly, is, appropriately, "Scientific Speculation.
Jueneman describes a highly speculative hypothesis that would account for radioactive decay by interaction with neutrinos rather than by spontaneous decay, and he notes that an event that temporarily increased the neutrino flux might "reset" the clocks. Jueneman, however, does not propose that decay rates would be changed, nor does he state how the clocks would be reset; in addition, there is no evidence to support his speculation.
Those mysterious neutrinos seem to be a hot topic! Slusher and Rybka also propose that neutrinos can change decay rates, citing an hypothesis by Dudley 40 that decay is triggered by neutrinos in a "neutrino sea" and that changes in the neutrino flux might affect decay rates.
This argument has been refuted by Brush 20who points out that Dudley's hypothesis not only requires rejection of both relativity and quantum mechanics, two of the most spectacularly successful theories in modern science, but is disproved by recent experiments. Dudley himself rejects the conclusions drawn from his hypothesis by Slusher and Rybkanoting that the observed changes in decay rates are insufficient to change the age of the Earth by more than a few percent Dudley, personal communication,quoted in 20, p.
Thus, even if Slusher and Rybka were correct--which they are not--the measured age of the Earth would still exceed 4 billion years. Judging from the above, it is easy to see that creationists are indulging in wild fishing expeditions. Compare their flighty arguments to the solid support provided by theoretical work, laboratory testing, and, for the shorter half-lives, actual observation, and add to that the statistical consistency of the dates obtained, including numerous cross-checks between different "clocks," and only one conclusion is left.
The radiometric decay rates used in dating are totally reliable. They are one of the safest bets in all of science.
The initial C content cannot be known. Various living samples give very different ratios. With at least one notable exception on the books, plants and animals get their carbon from the atmosphere. Plants take it in directly, and animals eat the plants. Thus, it gets passed up the food chain. It is not surprising, therefore, to find that the carbon in living plants and animals is in reasonable equilibrium with the atmospheric carbon Some creationists, however, have claimed that certain plants can reject carbon in favor of carbon Because of the chemical similarity of carbon and carbon, it is unlikely that such plants could deviate much from the ratio of C to C found in the atmosphere.
Neither freak cases nor small deviations pose much of a problem for radiocarbon dating, which, after all, works well with a wide variety of plant and animal species. Hence, we only have to worry about the initial concentration of C in the atmosphere.
Topic R1 shows that the level of C in the atmosphere has not varied appreciably over tens of thousands of years. Therefore, the initial C content is known for any reasonable sample! The notable exception involves certain mollusks, which get much of their carbon from dissolved limestone. Since limestone is very old it contains very little carbon Thus, in getting some of their carbon from limestone, these mollusks "inherit" some of the limestone's old age!
That is, the limestone carbon skews the normal ratio between C and C found in living things. If one dates such mollusks, one must be extra careful in interpreting the data. Not every mollusk shell presents such problems, and the dating of other material might yield a cross-check.
Further study might even allow correction tables. The discovery has strengthened the carbon method, not weakened it!
Over time 14C decays to nitrogen 14N. Most 14C is produced in the upper atmosphere where neutrons, which are produced by cosmic raysreact with 14N atoms. This CO2 is used in photosynthesis by plants, and from here is passed through the food chain see figure 1, below. Every plant and animal in this chain including us! Dating history When living things die, tissue is no longer being replaced and the radioactive decay of 14C becomes apparent.
Around 55, years later, so much 14C has decayed that what remains can no longer be measured. In 5, years half of the 14C in a sample will decay see figure 1, below. Therefore, if we know the 14C: Unfortunately, neither are straightforward to determine. Carbon dioxide is used in photosynthesis by plants, and from here is passed through the food chain. The amount of 14C in the atmosphere, and therefore in plants and animals, has not always been constant.
For instance, the amount varies according to how many cosmic rays reach Earth. Luckily, we can measure these fluctuations in samples that are dated by other methods.
Tree rings can be counted and their radiocarbon content measured. A huge amount of work is currently underway to extend and improve the calibration curve. In we could only calibrate radiocarbon dates until 26, years. Now the curve extends tentatively to 50, years. Dating advances Radiocarbon dates are presented in two ways because of this complication.
The uncalibrated date is given with the unit BP radiocarbon years before The calibrated date is also presented, either in BC or AD or with the unit calBP calibrated before present - before The second difficulty arises from the extremely low abundance of 14C.
Many labs now use an Accelerator Mass Spectrometer AMSa machine that can detect and measure the presence of different isotopes, to count the individual 14C atoms in a sample. Australia has two machines dedicated to radiocarbon analysis, and they are out of reach for much of the developing world. In addition, samples need to be thoroughly cleaned to remove carbon contamination from glues and soil before dating.
This is particularly important for very old samples.
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