Fission Track Dating as a Current Scientific Clock

By Frank Leibfarth

The Institute for Creation Research (ICR) has recently completed their multi-year project dealing with a scientific evaluation of the age of the earth and produced two book publications and an accompanying DVD. Within their research, the ICR research team makes many claims that geological evidence, including their findings dealing with dating rocks using the fission track dating method, provides substantial evidence for a young earth. In order to evaluate ICR's findings, one must first establish a proper methodology for fission track dating and compare ICR's methodology and finding to previous results.

Fission tracks, as physical structures, are simply linear tracks in rock crystals usually about 10-6 meters long. Fission tracks are most often caused by the spontaneous fission of the parent Uranium-238 atom into two daughter atoms of palladium-119. 238U is well documented in radiometric dating methods, with its decay into 206Pb with a half-life of 4.5 billion years. The spontaneous fission of 238U is much more rare, however, having a fission constant of λf = 8.46 * 10-17a-1, which is actually a number measuring the total number of fissions per year (Geochronology Group 2005).

Fission track dating is somewhat of an anomaly in the field of radiometric dating. All other radiometric dating techniques rely on the relative abundances of a known parent isotope of an element and its corresponding concentration of daughter decay products. Fission track dating, on the other hand, does not involve the measurement of daughter products, and the concentration of its parent isotope can be misleading because the parent element goes through other types of decay much more often than it goes through spontaneous fission. Unlike any other dating methods, however, fission tracks leave physical evidence of a radioactive process. Instead of comparing the ratio of isotopes, the age of a rock is determined by visually counting fission tracks of 238U. Fission track dating, although an unusual radiometric dating process, is accurate when used correctly and correlated with other dating methods.

In order to make fission tracks a useful method to date the earth, it must fit the criteria of good a natural clock. A note must be made that fission tracks are extremely thermally unstable (Geochronology Group 2005). The rock crystals will realign upon slight heating, either erasing or greatly shrinking most fission tracks. Therefore, fission tracks can only date the age of the last cooling of the rock, not necessarily the rock's correct geologic age of formation.

The first condition of a good natural clock is that it has a known initial condition. Fission track dating has a very good initial condition, being there are no fission tracks evident in a newly formed rock. A natural clock must also have a process with a constant rate with which measurements of age can be made. Once again, fission track dating fulfils this requirement, as the spontaneous fission of 238U atoms occurs at a constant rate under natural conditions.

The other two requirements for a natural clock are that the process of the clock must be irreversible, and it must have a known final condition. The spontaneous fission of 238U is irreversible, as there is no know process in the Universe that can fuse two palladium atoms together. The evidence of fission tracks, however, can be considered somewhat reversible, as they easily disappear with heating. This is why fission tracks can only measure the last cooling of the rock, not its age of formation. Fission track dating also has a known final condition; when all of the 238U atoms undergo fission, the constant rate of the clock will cease and no new tracks will appear.

As for the procedures used in fission track dating, first rock samples must be collected from a desired study location. According to the research done by ICR in their book Radioisotopes and the Age of the Earth, they collected various samples from "stratigraphically well-constrained volcanic ash or tuff beds from which Zircons would be extracted" (Snelling 2005:214). The samples were collected at various sites across the Western United States, including Arizona, Utah, and California. The ICR research team sent the collected samples to Geotrack International Laboratory in Melbourne, Australia, because of its specialization in fission track dating of minerals (Snelling 2005:229).

While in Melbourne, minerals were separated from the rock sample because only the hard minerals such as apatite, zircon, sphene, and natural glasses (including obsidian and pitchstone) can be accurately dating using fission tracks. The zircon grains were chosen for testing and, after a number of grinding and chemical treatment steps in order to prepare the sample, a thin grain (0.25 micro-meters wide) was then put into intimate contact with a mica resin and put into a reactor which irradiated the sample with neutrons in order to induce fission of the remaining Uranium-238 molecules (Geochronology Group 2005). As these molecules underwent fission, their tracks were etched into the mica resin, as the zircon grain was in effect made two-dimensional because of its small width.

In order to determine the density of zircon tracks within the crystal compared to the mica, which will correlate to the age of the grains, the researchers in Melbourne used a light microscope with a linear magnification of 1068 times. The researchers found the average values for the spontaneous track densities and compared them to the induced track densities to determine the ratio of parent to daughter fission isotopes. The ratio, when contrasted with the decay constant for spontaneous fission of Uranium-238 atoms, gives an estimate of the rock's last cooling date (Snelling 2005:232).

In ICR's research, 20 grains from each sample were tested, and an average age for each rock was calculated from these grains. As for the methods used by the ICR research team, they seem to be consistent with other research groups that do fission track dating. Also, there is absolutely no reason to doubt the credibility of the Geotrack International Laboratory. Overall, it appears the ICR research team was thorough and had solid scientific data, in the form of realistic ages with relatively small standard deviations, of the fission track dates for the rock samples which they collected.

Now that a method has been established, the data and results of the ICR research are able to be analyzed. The first conclusions that ICR mentioned, which can be found in Table 1, samples MT-3 and TT-1, is that the results for the Middle Cambrian samples "fail to agree with previously published results, showing major disagreement or discordance" (DeYoung 2005:105). The research team then explained that the discordance was probably related to the thermal histories of the rock and differences in measurement technique described by Snelling (2005:251). Furthermore, DeYoung (2005:105) discussed the regional history from the area where the samples were collected and asserted that some of the discordance could be attributed to the fact that tectonic movement in the Colorado plateau long after the Middle Cambrian caused the rocks to be heated above their annealing temperature and the clocks to be reset. The ICR team went on to state that almost all other results are concurrent with dates previously obtained for the rocks using other dating techniques. From this statement, ICR admits to believing that millions of years of decay appears to have occurred in these rocks assuming a constant rate of fission. ICR appears to have followed standard procedures and obtained typical results from the rock samples they collected, as one cannot find any serious flaw with their methodology or the results which they obtained.

Sample Name Location Published Ages (Ma) Fission Track Age Estimates (Ma)
PST-1 Snaggletooth area, CA 18.7 + - 1.5 24.6 + - 1.2
PST-2 Kingman , AZ 17.3 + - 0.4 20.9 + - 0.9
PST-3 Kingman , AZ 18.5 + - 0.2 20.9 + - 0.8
MMF-4 Montezuma Creek , UT 149.4 + - 0.7 148.7 + - 7.0
MMF-1 Montezuma Creek , UT 147.6 + - 0.8 137 + - 9
NMF-64 Notom , UT 106 + - 6 132 + - 10
MT-3 Grand Canyon , AZ 535 + - 48 74.6 + - 3.9
TT-1 Grand Canyon , AZ 563 + - 49 75 + - 7

With convincing scientific evidence, it appears ICR has found evidence for an earth with an age of millions or billions of years rather than one which supports their view of a young earth. The ICR research team concluded, however, that in order for the rocks tested to show millions of years of decay through fission track analysis, at some point in history there must have been accelerated nuclear decay because, according to scripture, the earth is only 6,000 years old. In summery, the ICR team found physical evidence of millions of years of nuclear decay and fit that data into a view of creation which they believe, on faith, to be true. Fission track dating shows absolutely no evidence for accelerated decay at any point in the earth's history.

ICR's hypothesis has one major question surrounding it: if the annealing temperature of a rock is very low for fission tracks, in the order of magnitude of 200o plus or minus 40o Celsius (Snelling 2005:250), how does the heat caused by accelerated nuclear decay not realign the rock crystals and erase the fission tracks? Any increased amount of nuclear decay, especially the large amount proposed by ICR, would be expected to considerably heat a rock and erase any evidence of fission tracks. Therefore, the hypothesis that ICR proposes makes no real sense as an attempt to fit millions of years of nuclear decay into the framework of 6,000 years.

The completion of the Institute for Creation Research studies had some solid scientific groundwork, as exhibited by the careful methods they used to test numerous rock samples using fission track dating. ICR once again fails to establish any credibility to their claim that the earth is only 6,000 years old, however, because they make outrageous claims about the scientific evidence which they have discovered. There is absolutely no physical evidence for a young earth or accelerated nuclear decay in the fission track analysis which ICR preformed. ICR's claims will have no significant impact on changing the modern scientific community's belief about the age of the earth.

Sources:
  1. DeYoung, Don. 2005. (pp100-106) Thousands not Billions. Master Books
  2. Geochronology Group. 2005. Fission Track Dating. http://www.minpet.ugent.be/fission.htm. Accessed November 27, 2005.
  3. Snelling, Andrew A. 2005. Fission tracks in zircons: evidence for accelerated nuclear decay. Chapter 4 (pp. 209-324) in L. Vardiamn, A. A. Snelling, and E. F. Chaffin (eds.) Radioisotopes and the Age of the Earth, Volume II: Results of a Young-Earth Creationist Research Initiative, Institute for Creation Research, El Cajon, California, 818 p.