KBS Tuff shows the flaws of radiometric dating (Talk.Origins)
- The KBS Tuff is an ash layer in the Koobi Fora Formation east of Lake Turkana in northern Kenya. It is significant because hominid fossils and artifacts were found in and under it, so its age gives a minimum age of the fossils. Various attempts to date it have yielded a wide range of different results, from 0.52 to 220 million years. The dating of the KBS Tuff exposes the fallacies of radiometric dating. "Good" dates are chosen to accord with accepted dates of fossils, while anomalous dates may not be reported at all. And in practice, it is impossible to be sure one has selected uncontaminated samples.
Source: Lubenow, Marvin L. 1995. The pigs took it all. Creation 17(3) (June): 36-38.
CreationWiki response: (Talk.Origins quotes in blue)
1. The KBS Tuff controversy illustrates many of the problems with radiometric dating, but it equally illustrates that the problems are not insurmountable.
The KBS Tuff (for "Kay Behrensmeyer Site," after the geologist who first described it) is a layer of redeposited volcanic ash, so it contains a mixture of older sediments, too. It is still possible to date the layer, but care must be taken to choose only the youngest rocks, else one would be dating the age of older sediments washed into the layer, not the age of the layer itself. This is what happened with the first ages reported from the tuff. In a study to test the feasibility of dating samples from the tuff, the samples were contaminated with non-juvenile components which could not be separated out, giving ages over 200 million years. It was recommended that new samples be collected from which suitable individual crystals could be separated (Fitch and Miller 1970). These new samples were dated at 2.61 +/- 0.26 million years, based on the 40Ar/39Ar dating method (Fitch and Miller 1970).
Discrepancies with this date soon turned up, though. Work with animal fossils, particularly of pigs, showed that the strata in question matched younger strata in the nearby Omo Valley. In its early stages, this fossil work was imprecise enough that the 2.61 Myr date could still be justified (Maglio 1972). However, the fossils continued to point to a younger date as the quality of the work on them improved (White and Harris 1977). And in 1975, another lab, using K-Ar dating, reported dates of 1.82 and 1.60 Myr (Curtis et al. 1975).
Fitch and Miller turned to an independent method to resolve the discrepancy, fission-track dating. Initial results gave an age of 2.44 +/- 0.08 Myr (Hurford et al. 1976). This fit well with the age of 2.42 Myr, which Fitch et al. (1976) recalculated from their original results. Subsequent 40Ar/39Ar measurements they took gave a scattering of ages from 0.52 +/- 0.33 to 2.6 +/- 0.3 Myr. They attributed the spread to reheating of the crystals after deposition. Paleomagnetic studies gave ambiguous results (Brock and Isaac 1974; Hillhouse et al. 1977).
The weight of evidence soon began to converge on an age near 1.9 Myr, though. A study of trace elements in the minerals showed that the KBS Tuff correlates with the H2 tuff in the Shungura Formation, uncontroversially dated about 1.8 Myr (Cerling et al. 1979). The 1.60 Myr age reported by Curtis et al. (1975) was found to be an error due to a faulty balance (Drake et al. 1980). A later fission-track study which took pains to eliminate possible errors gave an age of 1.87 +/- 0.04 Myr (Gleadow 1980). Because the controversy had become quite heated, another expert, Ian McDougall, was called in to do independent dating. He came up with an age of 1.89 +/- 0.01 using K-Ar dating and 1.88 +/- 0.02 using 40Ar/39Ar dating (McDougall et al. 1980; McDougall 1981, 1985). Geological evidence and the consistency of dates derived from various sources indicates that reheating after deposition is unlikely.
This is nothing less than a complete vindication of what creationists have been saying about radiometric dating. It is also an excellent example of just how good evolutionists are at rationalizing away problems. The funny thing is that Talk Origins is clearly totally blind to how well this illustrates the truth of what creationists say about the process of radiometric dating.
Here they have dates all over the place, not only by different methods, but by the same methods. Given this, it was the fossils that led the way. In the end they came up with three dates that agreed with each other and the fossils, all of which had also given erroneous results. Simply put, what happened here is that evolutionists kept making measurements until they found results that they liked.
The lessons to be learned from the KBS Tuff dating controversy are not that radiometric dating does not work, but that it works with some caveats.
- Some formations are easier to date than others. The KBS Tuff was particularly difficult to date because it included volcanic sediments of several different ages. Furthermore, it looked the same as other tuffs, so care was needed to make sure the same layer was being referred to in different areas. All of this requires careful work from knowledgeable geologists. Were it not for its importance to determining the ages of important hominid fossils, geologists probably would not have bothered with dating it at all.
But it still provides an excellent example of the process. The fact that these hominid fossils were so important and the KBS Tuff is particularly difficult, simply made the process more visible.
- Some dating techniques are simply inappropriate in some circumstances. As noted above, paleomagnetic study is not particularly useful at this site.
And those dating techniques that disagree with the fossils of a given location are considered inappropriate for the circumstances.
Discrepant dates are not dismissed out of hand without first looking for the sources of error, but failing this there is evidence that even the best of dates will be dismissed out of hand if they disagree with the fossils. The above statement also implies that if the dates are not discrepant, no one bothers to look for possible sources of error.
The original erroneous date by Fitch and Miller could be an accurate date of a roughly 2.5 Myr ash layer, present in neighboring areas but apparently eroded from the Koobi Fora Formation. Apparently, some pumice from that volcanic event had been incorporated into the KBS Tuff. Samples sent to an independent lab for "blind" dating confirmed its older age (Fitch et al. 1996). Alternatively, this and other discrepant ages may be due to contamination with older material. Such contamination caused ages in the 2.0 - 6.2 Myr range in the analysis of Curtis et al. (1975) until they revised their sample purification procedures. A high atmospheric argon contamination in their samples and analytical errors may have contributed, too (McDougall et al. 1980).
This just serves as another example of how things like contamination and analytical errors can be used to rationalize away any date that disagrees with theory. With the exception of the first one, no objective reason is given for accepting the sources of contamination other than the fact that these dates are older than the fossils say they should be.
The fission-track study which gave the 2.44 Myr age was the first such study to date zircons so young. The reanalysis by Gleadow (1980) noted problems with the standard methods and contributed new methodology for dealing with zircons with low track densities.
But since Gleadow got an age that evolutionists like, it is unlikely that his work will ever be similarly checked for possible sources of error.
The only sets of objective evidence shown by Talk Origins are the types of fossil found in the tuff and the fact that the 2.6 Myr date was close to the accepted date for a nearby formation. It is probably these that influenced all concerned to accept the 1.88 Myr age.
2. The different ages which were seriously debated for the KBS Tuff, from 1.6 to 2.6 million years, were never close to ages required by young-earth creationism.
These dates are at best only valid under uniformitarian geology theory. They are not valid under Flood geology. So this is just another example of "Your theory does not work under my theory, so your theory must be wrong."