Refuting "Radiometric Dating Methods Makes Untenable Assumptions!" | Debunking Denialism
The overall reliability of radiometric dating was addressed in some detail in a recent for countering claims of creationists on the reliability of geologic dating. Radiometric dating methods are very accurate and very trustworthy. Creationist arguments to the contrary are riddled with flaws, as is the. Long-age geologists will not accept a radiometric date unless it Creationists would generally agree with the above methods and use them in their . Critics claimed that the carbon results were 'too young' because the.
In the particular case that Morris highlighted, the lava flow was unusual because it included numerous xenoliths typically consisting of olivine, an iron-magnesium silicate material that are foreign to the lava, having been carried from deep within the Earth but not completely melted in the lava. Also, as the authors of the article were careful to explain, xenoliths cannot be dated by the K-Ar method because of excess argon in bubbles trapped inside [ Dalrymple ].
Thus in this case, as in many others that have been raised by skeptics of old-earth geology, the "anomaly" is more imaginary than real. Other objections raised by creationists are addressed in [ Dalrymplea ]. The overall reliability of radiometric dating was addressed in some detail in a recent book by Brent Dalrymple, a premier expert in the field. He wrote [ Dalrymplepg. These methods provide valid age data in most instances, although there is a small percentage of instances in which even these generally reliable methods yield incorrect results.
Such failures may be due to laboratory errors mistakes happenunrecognized geologic factors nature sometimes fools usor misapplication of the techniques no one is perfect. We scientists who measure isotope ages do not rely entirely on the error estimates and the self-checking features of age diagnostic diagrams to evaluate the accuracy of radiometric ages. Whenever possible we design an age study to take advantage of other ways of checking the reliability of the age measurements.
The simplest means is to repeat the analytical measurements in order to check for laboratory errors. Another method is to make age measurements on several samples from the same rock unit. This technique helps identify post-formation geologic disturbances because different minerals respond differently to heating and chemical changes.
The isochron techniques are partly based on this principle. The use of different dating methods on the same rock is an excellent way to check the accuracy of age results. If two or more radiometric clocks based on different elements and running at different rates give the same age, that's powerful evidence that the ages are probably correct. Along this line, Roger Wiens, a scientist at the Los Alamos National Laboratory, asks those who are skeptical of radiometric dating to consider the following quoted in several cases from [ Wiens ]: There are well over forty different radiometric dating methods, and scores of other methods such as tree rings and ice cores.
All of the different dating methods agree--they agree a great majority of the time over millions of years of time. Some [skeptics] make it sound like there is a lot of disagreement, but this is not the case.
The disagreement in values needed to support the position of young-earth proponents would require differences in age measured by orders of magnitude e. The differences actually found in the scientific literature are usually close to the margin of error, usually a few percent, not orders of magnitude! Vast amounts of data overwhelmingly favor an old Earth. Several hundred laboratories around the world are active in radiometric dating.
Their results consistently agree with an old Earth. Over a thousand papers on radiometric dating were published in scientifically recognized journals in the last year, and hundreds of thousands of dates have been published in the last 50 years. Essentially all of these strongly favor an old Earth. Radioactive decay rates have been measured for over sixty years now for many of the decay clocks without any observed changes.
And it has been close to a hundred years since the uranium decay rate was first determined.
A recent survey of the rubidium-strontium method found only about 30 cases, out of tens of thousands of published results, where a date determined using the proper procedures was subsequently found to be in error. Both long-range and short-range dating methods have been successfully verified by dating lavas of historically known ages over a range of several thousand years. The mathematics for determining the ages from the observations is relatively simple.
Rates of radioactivity One question that sometimes arises here is how can scientists assume that rates of radioactivity have been constant over the great time spans involved. Creationist Henry Morris, for example, criticizes this type of "uniformitarian" assumption [ Morrispg. But numerous experiments have been conducted to detect any change in radioactivity as a result of chemical activity, exceedingly high heat, pressure, or magnetic field. None of these experiments has detected any significant deviation for any isotope used in geologic dating [ Dalrymplepg.
Scientists have also performed very exacting experiments to detect any change in the constants or laws of physics over time, but various lines of evidence indicate that these laws have been in force, essentially the same as we observe them today, over the multi-billion-year age of the universe.
Note, for instance, that light coming to Earth from distant stars which in some cases emanated billions of years ago reflects the same patterns of atomic spectra, based in the laws of quantum mechanics, that we see today.
What's more, in observed supernova events that we observe in telescopes today, most of which occurred many millions of years ago, the patterns of light and radiation are completely consistent with the half-lives of radioactive isotopes that we measure today [ Isaakpg.
As another item of evidence, researchers studying a natural nuclear reactor in Africa have concluded that a certain key physical constant "alpha" has not changed measurably in hundreds of millions of years [ Barrowpg. Finally, researchers have just completed a study of the proton-electron mass ratio approximately Thus scientists are on very solid ground in asserting that rates of radioactivity have been constant over geologic time. The issue of the "uniformitarian" assumption is discussed in significantly greater detail at Uniformitarian.
Responses to specific creationist claims Wiens' online article, mentioned above, is an excellent resource for countering claims of creationists on the reliability of geologic dating. In an appendix to this article, Wiens addresses and responds to a number of specific creationist criticisms. Here is a condensed summary of these items, quoted from Wiens' article [ Wiens ]: Radiometric dating is based on index fossils whose dates were assigned long before radioactivity was discovered.
This is not at all true, though it is implied by some young-earth literature. Radiometric dating is based on the half-lives of the radioactive isotopes. These half-lives have been measured over the last years. They are not calibrated by fossils. No one has measured the decay rates directly; we only know them from inference. Decay rates have been directly measured over the last years.
In some cases a batch of the pure parent material is weighed and then set aside for a long time and then the resulting daughter material is weighed. In many cases it is easier to detect radioactive decays by the energy burst that each decay gives off. For this a batch of the pure parent material is carefully weighed and then put in front of a Geiger counter or gamma-ray detector.
These instruments count the number of decays over a long time. If the half-lives are billions of years, it is impossible to determine them from measuring over just a few years or decades.
The example given in the section [in Wiens' article] titled, "The Radiometric Clocks" shows that an accurate determination of the half-life is easily achieved by direct counting of decays over a decade or shorter.
Additionally, lavas of historically known ages have been correctly dated even using methods with long half-lives. The decay rates are poorly known, so the dates are inaccurate. Most of the decay rates used for dating rocks are known to within two percent.
Such small uncertainties are no reason to dismiss radiometric dating. Whether a rock is million years or million years old does not make a great deal of difference. The second worry is that extra amounts of the daughter element may enter the system after the original formation of the rock, thus giving the impression that more of the parent element has undergone radioactive decay than has actually been the case.
In both the examples I have described, there are ways of checking that such intrusions have not occurred. Minerals can be tested for their capacity to absorb extra argon under experimental conditions designed to resemble their natural environment, and geologists can screen out, in this way, minerals that are liable to give erroneous results. In the second case, the existence of two separate decay processes provides a check on the assumption that the system has not been contaminated.
If extra lead were to have been absorbed in the rock after the original formation, the new lead would have caused the calculated ages of the rock to diverge unless it contained the right proportion of lead to lead If the ratio of lead to lead in the newly introduced rock were greater than the ratio of lead to lead found in an uncontaminated system, the method of dating based on the decay of uranium to lead would give a relatively higher value than the method of dating based on the decay of uranium to lead Obviously just the opposite holds when the ratio of lead to lead is too small.
Hence someone who supposes that concordant ages are inflated must believe that the contaminating lead contained just the right proportion of the two isotopes.
I want to emphasize that I have only dealt with two of the commonly used radiometric methods, and I have only outlined the most elementary of the checks that geologists use in applying them. More details can be found in Eicherchapter 6; and Faul From what I have said it might seem that the assignment of ages to rocks is still a bit uncertain. However, I hope that it will help to quell anxieties when I point out that a large number of independent methods have been applied to a vast array of different rocks.
The result of this enormous array of tests is a consensus. The ages assigned to various rock strata bearing distinctive types of fossils show extraordinary agreement.
The many independent computations of the age of the earth during the last three decades almost invariably yield a figure between 4. Of course, there are occasional puzzling discrepancies. But geologists take these as signs that unanticipated factors have affected the system from which the result was obtained. They know that geological clocks, like other clocks, can go wrong. Frequently, further investigation dissolves the anomaly by showing what the interfering factor has been.
Radiometric Dating and Creation Science
Let us now take up some of the Creationists' attempts to criticize radiometric dating. The main lines of attack are laid down by Morris. He begins by identifying three assumptions of the use of radiometric techniques: The system must have been a closed system. The process rate must always have been the same" Morris a, We have already discussed statements akin to Morris's first and second assumptions. As will become clear shortly, the status of the third is a little different.
Unsurprisingly, Morris believes that he can provide good reasons for doubting each of these assumptions in the case of every application of every method. He claims that none of the assumptions is "provable, testable, or even reasonable" Morris a, Here are the reasons: There is no such thing in nature as a closed system. The concept of a closed system is an ideal concept, convenient for analysis but non-existent in the real world.
The idea of a system remaining closed for millions of years becomes an absurdity. It is impossible to ever know the initial components of a system formed in prehistoric times. Obviously no one was present when such a system was first formed. Since creation is at least a viable possibility, it is clearly possible that some of the "daughter" component may have been initially created along with the "parent" component. Even apart from this possibility, there are numerous other ways by which daughter products could be incorporated into the systems when first formed.
No process rate is unchangeable. Every process in nature operates at a rate which is influenced by a number of different factors.
If any of these factors change, the process rate changes. Rates are at best only statistical averages, not deterministic constants. Morris a, These rejoinders make it apparent that Morris's formulations of the assumptions underlying radiometric dating are only akin to the assumptions examined above. When geologists calculate the ages of rocks, they do assume that the system under consideration has remained closed in one particular respect. They suppose that none of the daughter element has been added or subtracted.
However, this does not commit them to the idea that the system was completely closed, that it engaged in no exchange of matter or energy with the environment. Like his memorable argument about the evolving junkyard, Morris's first reply only demonstrates his lack of understanding of basic concepts of physics. The crucial question is whether we can ever be justified in believing that the system was never contaminated by extra amounts of the daughter element.
I have tried to explain how geologists can sometimes obtain good evidence for this conclusion. Similarly, the second point is misguided.
Geologists do not have to suppose that the system originally contained none of the daughter element. What is important is that they be able to compute the amount of the daughter element originally present.
Clearly, it is required only that D0 be known, not that it be zero. It is perfectly possible to have excellent evidence for statements about events and situations that no human has observed. Geologists draw conclusions about the composition of original rocks by applying claims about the possibilities of incorporating elements into minerals, claims that can be tested in the laboratory.
So, for example, the thesis that certain minerals would have contained no original argon rests on a perfectly testable and well-confirmed claim. While those minerals were in the molten state, prior to the solidification of the rock, argon would have diffused from them.
It is only after the molten rock has solidified that the argon formed through radioactive decay becomes trapped within it. Obviously, what is being applied in this case is our knowledge of the physical and chemical interactions of minerals and elements. Morris's third assumption, and his attempt to undermine it, raises a new issue.
In deriving equation 4from which rock ages can be computed, I employed equation 1the equation of radioactive decay. I asserted that l, which measures the rate of decay, is a constant.
How Good Are Those Young-Earth Arguments?
Morris suggests that the assertion is unwarranted. However, the claim that l is a constant does not descend out of thin air. It is the result of our knowledge of nuclear physics. Although the sciences sometimes teach us that the rate at which a process occurs can be affected by a number of factors, as when we learn that the rate at which water boils is affected by the pressure or that the rate at which mutations occur varies with X-ray irradiation, what we sometimes discover is that a process is impervious to outside influence.
Precious little affects the time of passage for a light ray between two points. Similarly, nuclear physics tells us that radioactive decay is well insulated against external interference. The reason is that the emission of particles from an atomic nucleus is under the control of forces that are enormously more effective at short distances than the forces at work in most physicochemical reactions. Extensive attempts to modify these rates under a variety of physicochemical conditions have produced no effects.
For example, his chief weapon in arguing for the possibility of variable decay rates is a vague proposal that the capture of free neutrons or the impact of neutrinos could affect decay constants Morris a, The latter idea is linked to a paragraph quoted from a "Scientific Speculation" column. But neither of these processes would affect rates of decay; even granting the possibility of change by neutrino impact or the practical likelihood of neutron capture, the result of these processes would be a modification not of the decay rate, but of the decaying nucleus.
How Good are those Young-Earth Arguments: Radiocarbon Dating
The old nucleus, which had been decaying at its specific rate, would be changed to a new nucleus, which would then change at its specific rate. Note that if processes like these were to occur, they would be detectable since two separate sets of daughter elements would be produced. Morris's speculations are based on confusion.
Morris then goes on to ignore the methods that geologists employ to ascertain the original amount of daughter element present in the rocks they attempt to date. His discussion of uranium-lead dating contains no mention of the simple technique for computing the initial abundance of lead that I described above. Needless to say, nothing is said about more sophisticated methods.
His treatment of potassium argon dating includes the statement: However, argon is an inert gas, which does not become chemically bound to potassium minerals.