Carbon dating - RationalWiki
Radioactive decay of naturally occurring and human generated 14C allows us to determine age by measuring the amount of radiocarbon left in a sample compared to how much An interactive introduction to radiocarbon dating via AMS at NOSAMS. Problems or questions about the site, please contact. The possibility of radiocarbon dating would not have existed, had not 14C had the The statement of the Nobel Committee represents an unusual degree of foresight, The problem was that, even at 10 dpm/g, the 14C would be unmeasurable! .. 7 shows, for example, that the excess atmospheric 14C injected in the. 14C Dating History: Early Days, Questions, and Problems Met. 3 given as ± .. Remarks on Normal Pretreatment and Special Samples. The reservoir.
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.
- Radiocarbon Data & Calculations
- What is Carbon Dating?
- How Good Are Those Young-Earth Arguments?
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.
Carbon 14 Dating - Math Central
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.
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!
By the way, shouldn't the creationist be worried over the old, carbon age of the limestone? Why is it that limestone has so little C in it? Partial contamination, say of a block of wood, may affect its different parts to different degrees. Insect burrows, cracks, and partial decay may allow contamination later on to affect those portions of the sample unequally. However, there are laboratory techniques, often ingenious, for dealing with such problems.
If the sample shows evidence of being hopelessly contaminated it is pitched. Some samples, such as a section of a tree trunk, may well contain material of considerably different ages. The interior portion of a tree trunk could easily be several hundred years older than the outer portions. In summing up this point, we do know within good limits what the initial C was for any reasonable sample.
A sample will not have different ratios of carbon unless it has been contaminated or reflects a genuine range of ages. It is very difficult or impossible to prove that a given sample has not been contaminated. Parent or daughter products could have leached in or out of the sample. In the case of carbon dating, the daughter product is ordinary nitrogen and plays no role in the dating process. We are only interested in tallying the original C still present in the sample, the surviving "parent" isotope.
The C that is incorporated in the carbon structure of cellulose and the other structural materials of living plants and animals is not going to do much migrating after burial. If structural carbon migrated easily there soon wouldn't be any cellulose, lignin, chitin or other structural carbon compounds left in the soil!
A piece of wood, for example, would soon turn into a formless cloud of graphite or soot in the soil, with perhaps a little ash marking the original shape! Clearly, that is not something which normally happens. Residues or solutions which do migrate can usually be washed out of the structural matrix of the sample with various chemicals. To put it another way, we might imagine a piece of buried wood as being something like a sponge. Any carbon-containing liquid originally possessed by that sponge might well leak over time and be replaced by something else.
However, unless the sponge itself disintegrates, the carbon which holds its fibers together must stay put. Thus, by choosing a sample that is structurally intact, one may rule out any significant loss of C If the liquid impurities in our sponge can be washed and squeezed out, or estimated in some way, then we may be able to date the sponge structural component of our sample itself and get a good date even if non-structural carbon had been lost in a manner that would upset the isotope ratio.
A sample, of course, can be contaminated if organic material rich in fresh atmospheric C soaks or diffuses into it. Such contamination may occur in the ground or during the processing of the sample in the laboratory. However, such contamination will make the sample appear younger than its true age. Consequently, with regards to carbon dating, creationists are barking up the wrong tree on the contamination issue!
Laboratories, of course, do have techniques for identifying and correcting contamination. There are various methods of cleaning the material, and the activity of each rinse can be measured. Lab contamination and technique can be checked by running blanks.
A careful choice of samples will often minimize contamination. Dating various portions of a sample is another kind of check that may be performed. Often there are cross-checks. Samples from top to bottom of a peat bog gave reasonable time intervals Science, vol.
The calibrated C method confirmed Egyptian records, and most of the Aegean dates which were cross-dated with Egyptian dates were confirmed American Scientist, May-June The marvelous agreement with tree-ring data, after correction for variations in the earth's magnetic field, has already been mentioned.
Carbon dating thus presents a deadly challenge to young-earth creationists. If an old date is reasonably accurate, they're out of business; if an old date is bad due to contamination, then they are still out of business because the true date is most likely older still. It hardly seems fair, but that's the way it is. With that in mind, let's look at a few carbon dates.
Egyptian barley samples have been found which date to 17, years old Science, April 7, On page the author explains some of the professional care which stands behind his use of the carbon method.
A wooden walkway buried in a peat bog in England has been dated to about BC by the carbon method Scientific American, Augustp. Odd, that Noah's flood neither destroyed it nor deposited thick sediments on top of it!
Jennifer Hillam of the University of Sheffield and Mike Baillie of Queen's University of Belfast and their colleagues were able to date the walkway by a second method, i.
They found out that the walkway, known as the Sweet Track, was built from trees felled in the winter of BC. Organic materials, which require the most processing, are limited to younger ages by their corresponding process blank. Due to counting and measurement errors for the blanks and samples, statistical errors are higher for very old samples. Thus, ages are limited by the age of the process blanks more on that below and by the statistical uncertainty of the 14C measurement. For small samples, blank contribution as a fraction of sample mass becomes a more important term, so a mass balance blank correction is applied.
This correction is performed as follows: AMS results are calculated using the internationally agreed upon definition of 0.
Calibration of radiocarbon dates
The value used for this correction is specified in the report of final results. Fractionation is the term used to describe the differential uptake of one isotope with respect to another. While the three carbon isotopes are chemically indistinguishable, lighter 12C atoms are preferentially taken up before the 13C atoms in biological pathways. Similarly, 13C atoms are taken up before 14C. The assumption is that the fractionation of 14C relative to 12C is twice that of 13C, reflecting the difference in mass.
Fractionation must be corrected for in order to make use of radiocarbon measurements as a chronometric tool for all parts of the biosphere. Using this measurement also corrects for any mass-dependent fractionation within the AMS system.
The Remarkable Metrological History of Radiocarbon Dating [II]
An external error is calculated from the reproducibility of multiple exposures for a given target. The final reported error is the larger of the internal or external error, propagated with errors from the normalizing standards and blank subtraction.
It should be noted that the reported error is an estimate of the precision repeatability of measurement for a single sample. Due to variability in sample homogeneity, sample collection, and sample processing, the variability of replicate samples reproducibility is generally greater than the reported error for a single sample.