Appendix:  Radiometric Dating

by | Mar 17, 2023 | Age of the Earth, Geology and the Flood, Jesus and Science

The rock shown is Calcite with inclusions of Uranophane, a uranium silicate from my thesis area in Mexico.

Appendix:  Radiometric Dating

Stephen Mitchell

From: A Texas-Sized Challenge to Young Earth Creation and Flood Geology,

Published 2018, Meadville, PA;  Christian Faith Publishing, Inc.

When a murder has been committed and a medical examiner arrives at the scene, one of the most important questions that he has to answer is: When was the time of death? The TV programs show over and over again that measuring the body temperature is one method that is used. If the death was recent enough, its temperature may still hold remnants of its temperature from life. That temperature often will decay at a predictable rate: 1.5° (2.7°F) per hour until it reaches the temperature of its environment (Claridge 2015). TV detective shows also point out that murderers have numerous ways to trick the medical examiners. The basic predictable rate requires that the conditions be right for the measurement to be accurate. If the body is put in extra cold conditions, the temperature will drop more quickly. Smaller bodies cool more quickly than larger bodies. The fact that there are situations when this method does not work does not mean that the method is not useful. The time of death based on the decay in body temperature uses very straightforward measurements of physical properties and changes that are well understood and the method has been tested repeatedly. One can be confident that if the proper conditions existed, this measurement will give a trustworthy answer. Even in the best of cases, the examiners recognize that the measurements are not perfect and the ambient conditions were variable to some extent. There is always a time range given because the measurements just cannot be precise enough to tell the precise moment of death.

 The forensic medical examiner is quite analogous to the physicist using radiometric dating. Certainly, the time ranges that they are attempting to measure are radically different. Instead of hours, the physicist uses different methods to date things that might be hundreds or even billions of years old. Fortunately, normally knowing the exact year for rocks is not that important in most cases. Both are using physical measurements of properties that varied over time. In each case, the process that leads to the change is well understood. Although the decay in body temperature may be easier for nonscientists to understand, radioactive clocks should give more consistent answers for the time ranges that they are trying to measure. This may seem surprising but they are just less susceptible to environmental changes and thus more predictable as clocks. Without giving in any sense a thorough explanation, I will give my perspective on this valuable scientific approach.

How does a radiometric clock work? First it is important to understand what radioactivity is. Atoms of the same element all have the same number of protons and electrons. However, they can still be different, based on the number of neutrons. Thus, elements may take different forms, known as isotopes, based on differing numbers of neutrons. Some isotopes are stable for long periods of time, but others are unstable. The unstable atoms break down, emitting radiation and in the process, change into other elements that are also usually unstable, a process known as decay. From a human standpoint, it is impossible to say when a particular atom will decay and change into another element. That would seem to make such a process particularly badly suited for use as a clock. However, what is totally unpredictable for one particular atom turns out to be extremely consistent for large populations of atoms. For large sets of atoms, each isotope will decay at an average rate such that for a particular time, known as the isotope’s half-life. Half of the atoms will decay, emitting radiation and changing from one element to another. Isotopes that decay faster have shorter half-lives. The most common isotope of uranium, 238U, is unstable. It decays, sending out an alpha particle and changes into the thorium isotope, 234Th. It is not a fast process. We still have 238U around. If you had one gram of 238U, then 4.468 million years later, you would have 0.5 grams of 238U. The rest would have decayed into 234Th. The thorium isotope is also unstable, so part of it would have decayed into protactinium. Unstable 238U is transformed through fourteen steps into lead, 208Pb (Figure 108).

Figure 108. The decay series for 238U, showing the element isotopes, the decay half-lives and the type of radiation emitted at each transition (Duval et al. 2004).

    Such reaction chains have been developed for many different radioactive isotopes. In fact, many different chains are documented and are candidates for use as radiometric clocks. A fair question might be, do we understand the physical decay process well enough to consider radioactive clocks reliable, even theoretically? Could this be some sort of “black box” where an analysis is performed and numbers generated, but scientists are really totally wrong about what is happening? How stable is the process of radioactive decay? Many experiments have been devised to evaluate the constancy of the rate of decay. Probably many investigators wanted to be the first to find the exception, the situation, or conditions that would give a different answer. It would have been much more exciting to be able to announce that they had discovered a way to slow or speed the decay rate. The actual result was to confirm that the decay rate is very constant regardless of extremes in temperature, pressure, electromagnetic field or gravity field. Why? Dr. G. Brent Dalrymple, a recognized expert on radiometric dating, helps with this explanation:

There are two basic reasons why significant changes in rates of decay are not expected. First, the nuclei of atoms are extremely small and well insulated by their cloud of orbiting electrons. These electrons not only separate nuclei sufficiently that they cannot interact, but also provide a “shield” that prevents ordinary chemical or physical factors from affecting the nucleus. Chemical activity in an atom, for example, occurs almost entirely among the outermost electrons and does not involve the nucleus at all. Likewise, the “compressibility” of a substance may result in slight changes in the configuration of electrons but has no effect on the nucleus.

      Second, the energies involved in nuclear changes are 109 times greater than those involved in chemical activity and 104 to 105 times greater than the energies that bind the electrons to the nucleus . . . Except for nuclear reactions, such energies are generally unavailable in natural processes such as those that form, change, and destroy rocks on the earth and in the Solar System. (Dalrymple, 1991)

 Overall, it seems that the physics required to explain radiometric dating is well understood and is constantly used in many other processes. The rate of decay has been experimentally tested rigorously for variations based on natural changes and found to be constant. We see good theoretical explanations for why the experimental data should be this way. If there are problems with this clock, they must come from somewhere other than the theory.

 

Does this prove that radiometric dating is valid? Hardly. Not all theories work in the real world. It is conceivable that one could theoretically date materials using some physical change, but it might be practically impossible to make meaningful measurements. For example, real measurements might be made useless because the measurements would be too difficult to make, or technology might not be available to measure the properties consistently. It also is important to look at what assumptions are necessary for the methodology to give meaningful measurements. It could be that the necessary assumptions would be so unjustified and untestable that the results could not be believed. Let’s look at radioactive decay and consider its methodology.

 

The first test of radiometric dating was published by Ernest Rutherford in 1905. He recognized that helium is a byproduct of radioactive decay and that it would otherwise be virtually absent from many minerals. His early measurements were encouraging but demonstrate some of the concerns. He proposed that by knowing the rate of helium production and the amount of helium in rocks, one could calculate an age for a rock. Measuring equipment at the time was far less accurate and reliable than today, but that was perhaps the smaller problem. He had to make the assumption that all the helium generated by radioactive decay stayed in the rock. He recognized this concern, knowing that helium, as an inert gas, is just too mobile. Rutherford published a date of 497 Ma (millions of years ago) for a fergusonite mineral for his first published example and called it a minimum age. The assumption that all the helium remained was not necessarily valid and could not be proven. If some of the helium escaped the rock, then the ratio of uranium to helium would be higher and the rock would seem younger than it actually is. At best, this could only be used for a few pristine igneous rocks where one could make the case that they had been undisturbed since formation. Rutherford’s analysis also had the problem that as one standalone measurement, there was no way to validate it by comparing it to other methods. If no other possibilities had come forward, radiometric dating would have been of limited value and its conclusions been controversial and often unaccepted.

I will not try to give a technical explanation for the many techniques used in modern radiometric dating methods. Good resources for such would include The Age of the Earth by G. Brent Dalrymple, the University of Wisconsin Green Bay PowerPoint: https://www.uwgb.edu/…PPT/340Ra…; The Bible, Rocks and Time by Davis A. Young; and Ralph F. Stearley, The Dynamics of Dating (http://www.reasons.org/articles/the-dynamics-of-dating ) and Radiometric Dating: A Christian Perspective (http://www.asa3.org/ASA/resources/Wiens.html ) by Roger C. Wiens. The last three are particularly good because they are by Christians and give good Christian perspectives. This is useful for those who have concerns and difficulties when reading answers from scientists that are not Christians.  We recognize that there are many reasons why radiometric dating might not work for a particular rock. Many rocks have had complex histories that may have involved partial melting, alteration that occurred as groundwater and other fluids percolated through them and other processes. With so many things that could go wrong, is it possible to really trust this methodology? Here are some simplified points to consider when evaluating the validity of the methodology used to date rocks using radiometric techniques.

  1. Over forty different measurement techniques are used. In many cases, the same rock can be dated using multiple independent methods. Such cross-checks provide strong validation that such dates are valid.
  2. Today’s instruments are extremely precise and capable of measuring isotopic concentrations in tiny, microscopic minerals. This helps both in terms of the precision of the measurement and by allowing measurement of elements within the lattice of crystals that are far less altered and more pristine than were available in earlier days. Zircon is the favorite mineral because, though it forms as only traces in most rocks, it is very durable and typically has uranium and thorium incorporated into its crystal structure. Isotopes within tiny crystals of zircon can be measured today and provide valuable data.
  3. Techniques are available that do not demand major assumptions about the original isotopic composition of the rocks. The assumption that we know the original composition is usually difficult to test. Removing this assumption raises confidence in dates. One way is to measure the isotopic ratios in different minerals within the same rock and from different rocks within a given igneous body. When no other processes have intervened, the ratios can be plotted to align and point to a date without knowing the original composition. If they do not align, this provides clues about what other processes have occurred.
  4. Several techniques are self-checking. That is to say that when the data are plotted, bad data can be identified and often corrected.
  5. Most alterations tend to make a rock appear to be younger than it is. Many of the “daughter” isotopes, those that result from decay, tend to be somewhat more mobile than the original isotope. If less of the daughter is found, then the resulting ratios will tend to be enriched in the parent isotope and make the rock look as though less time has elapsed than really did. This was the case with helium in Rutherford’s early work.

 What might make rocks look older than they are? In this case, we are talking about not just a bit older. We mean radically older. What would make a rock that is only ten thousand years old have measurements that appear to be one hundred million years old? YEC scientists have spent much effort trying to identify any possible explanations. They dug into every aspect of the theory and the methodology. YEC geologist John Woodmorappe has extensively searched the literature for examples of radiometric dates that are questionable (Woodmorappe 1999). It is common for scientific writers to express concerns and uncertainties about their data and interpretation. Woodmorappe has a large collection of such comments and other inconsistencies. It would be quite a job to investigate each of his interpretations.

 The most extensive YEC study was the “Radioisotopes and the Age of the Earth” (RATE) study initially published in 2000, and then in 2005 as a final report (Vardiman 2000; Vardiman 2005). Did the studies demonstrate any serious problems with radiometric dating assumptions or methodology? A reader might ask, did the RATE investigators come into their study with open minds to learn whether or not the method was valid? Perhaps it is more likely that, given their interpretation of the Bible, that their conclusions were forgone. They certainly gave their financial contributors a lot of material as each report is over six hundred pages long. I suspect that those convinced that the earth is young prior to the report were thoroughly pleased. Scientists in general and particularly those who are experts in nuclear physics were not impressed. Perhaps more telling, there does not seem to be any evidence that technically minded individuals with no prior position see the RATE report as raising any particular doubts in radiometric dating.

 

In my opinion, they have not found any evidence that really causes any substantial doubt in radiometric dating. A number of Web sites are available that provide specific critiques of their report. For example, Jeff Zweerink of Reasons to Believe here: http://www.reasons.org/articles/comments-on-the-rate-project and Randy Isaac of the American Scientific Affiliation, an organization of scientists who are Christians: http://www.asa3.org/ASA/education/origins/rate-ri.htm

 

The researcher’s extensive efforts in effect demonstrate several positive points that support conventional dating:

  1. Large numbers of measurements have been made from around the world consistently point to the dated rocks being much older than the YEC time frame allows. These are not flukes. They are the rule not the exception.
  2. Most measurements are stratigraphically consistent. They are not randomly distributed.
  3. No easy errors in either the theory or methodology exist that invalidate this methodology. The hope for an Achilles’ heel that will make radiometric dating just go away does not seem to be coming.

 

For example, DeYoung (2000) lists the following proposals to address the problem of these old dates:

  1. Conventional assumption: Constant rate of decay in the past. If one assumes that today’s rates worked in the past, then this is a major problem, given the preponderance of older dates.

DeYoung proposal: a dramatic temporary increase or increases in decay at some point in the past, creating a large rapid increase in daughter products (during creation and Noah’s flood). This would be a bit more tenable if (a) the earths strata supported such a flood interpretation, but the first part of this book demonstrated that they do not and (b) there was physical evidence consistent with such an increase, such as melting or evidence of the heat associated with such rapid decay. Most radioactive dating of rocks commonly uses igneous rocks such as granites. Even so, potassium feldspars are major components of arkosic sandstones. If such a dramatic increase in radioactivity occurred in them, then these sedimentary beds would show dramatic evidence of the associated heating.

 

  1. Conventional assumption: Isotope composition has not changed by fractionation over time. There does not seem to be any physical explanation for why we should expect isotopes to be fractionized significantly, let alone routinely. If they are not, then it is fair to assume that radioactive decay is the major mechanism responsible for today’s isotopic composition.

DeYoung proposal: isotopes ratios altered, not just by decay but by fractionation. Evidence for this significant fractionation is apparently missing, but it would be necessary for the YEC timeline. There seems to be no particular logic to use to assume that ages that fit the stratigraphic order are due to fractionation.

 

  1. Conventional assumption: It is possible to find rock samples that have been closed systems for eons of time. That is not to say that all rocks were closed or even that they were closed for all elements. Geochronologists do say that it is possible to identify clean, unaltered samples and their analysis give valid results and that it is also possible to distinguish between valid and invalid results.

DeYoung proposal: parent or daughter atoms have moved into or out of rocks. Again, all recognize that many processes alter rocks. The geochronologist’s assumption is that samples and scenarios can be identified that give meaningful results. The YEC proponent must believe that all the scenarios identified are off in major ways.

 

Radiometric dating methods have been through heavy scrutiny both by the regular scientific community and YEC skeptics. There seems no consistent reason to doubt its general credibility. So far, 14C dating has not been discussed here. Is it to be believed? Many nonscientists think of this method as the only form of radiometric dating, while in fact, it was not even discovered until 1949 and not used for dating until the 1960s. The method recognizes that living plants and animals have nearly constant ratios of 14C and 12C and that ratio is fixed at death. At that point, the radioactive 14C begins to decay and the ratio begins to change. With a half-life of 5,730 years, 14C dating does not help much for most of the geologic column. It can be used only for samples younger than fifty to sixty thousand years. While that is old enough to be a significant problem for YEC positions, it does not hit much of the geologic record by the conventional timeline. This method has a well-known set of possible problems that can invalidate it, but it offers opportunities for testing it with material of known dates. While not every analysis has proven to be correct, even YEC geologist, Andrew Snelling admits that “radiocarbon ‘dates’ for the last 2,000 years seem to show a generally good correlation with historically verified artifacts and specimens” (Snelling 2009). It seems a bit convenient to me for a technique to be valid until it begins to give problems for the YEC position. Snelling again appeals to accelerated decay during creation and the flood.

 

It is the position of this book that the geologic record alone, without any of the radiometric dating demonstrates that the earth is far older than the YEC position demands. Radiometric methods do not rely on standard geologic methods. They are independent evidence for the antiquity of the earth. The RATE study recognized two problems for which they have no answers for today: the heat and radiation that their accelerated radioactive decay model demands. Such heat and radiation would not just leave evidence; it would end life on the planet. It is as always recognized that it is not beyond God’s power to decay elements rapidly and make the world appear old radiometrically. However, so far it looks like the only purpose would have been for God to have made the earth appear old. Such effort at deception seems far out of character for the God of the Bible.

 

 

References Cited:

Claridge, J. 2015. Measuring Body Temperature. Retrieved October 12, 2015, from Explore Forensics: http://www.exploreforensics.co.uk/measuring-body-temperature.html

Dalrymple, G. B. 1991. The Age of the Earth. Stanford: Stanford University Press.

DeYoung, D. 2000. “Radioisotope Dating Review.” In A. S. L Vardiman, Radioisotopes and the Age of the Earth (pp. 42–47). El Cajon, CA: Institute for Creation Research, Creation Research Society.

Duval, J., Fukumoto, L., Fukumoto, J., and Snyder, S. 2004. “Uranium.” Retrieved from: Geology and Indoor Radon in Schools of the Palos Verdes Peninsula Unified School District, Palos Verdes Peninsula, California School District, Palos Verdes Peninsula, California: https://pubs.usgs.gov/of/2004/1050/uranium.htm

Isaac, R., 2007, “Assessing the RATE Project; Essay Review”; Perspectives on Science & Christian Faith, https://www.asa3.org/ASA/education/origins/rate-ri.htm

Snelling, A. 2009. Earth’s Catastrophic Past, Vol. 1 and 2. Dallas: Institute for Creation Research.

Vardiman, L., Snelling, A., Chaffin, E., 2000. Radioisotopes and the Age of the Earth: A Young-Earth Creationist Research Initiative. El Cajon, CA: Institute for Creation Research and the Creation Research Society.

———. 2005. Radioisotopes and the Age of the Earth: A Young-Earth Creationist Research Initiative, Vol II. El Cajon, CA: Institute for Creation Research and the Creation Research Society.

Wiens, R.C., 1996, “The Dynamics of Dating” Reasons to Believe website: https://reasons.org/explore/publications/articles/the-dynamics-of-dating

Wiens, R.C., 2002, “Radiometric Dating: A Christian Perspective”, https://www.asa3.org/ASA/resources/Wiens.html

Woodmorappe, J. 1999. The Mythology of Modern Dating Methods. El Cajon, CA: Institute for Creation Research.

Young, D., and Stearley, R. 2008. The Bible, Rocks and Time. Downers Grove, IL: IVP Academic.