Browse Search Feedback Other Links Home Home The Talk.Origins Archive: Exploring the Creation/Evolution Controversy

Index to Creationist Claims,  edited by Mark Isaak,    Copyright © 2005
Previous Claim: CD020   |   List of Claims   |   Next Claim: CD101

Claim CD031:

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.


Lubenow, Marvin L. 1995. The pigs took it all. Creation 17(3) (June): 36-38.


  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.

    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.
    Note that different methods give the same results when known sources of error are removed. K-Ar, 40Ar/39Ar, and fission-track methods ultimately all gave the same results. These results were correlated with strata of the same age at other locations on the basis of fossil and trace element analysis.

  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.


MacRae, Andrew. 1998. Radiometric dating and the geological time scale: Circular reasoning or reliable tools?


  1. Brock, A. and G. Ll. Isaac. 1974. Paleomagnetic stratigraphy and chronology of hominid-bearing sediments east of Lake Rudolf, Kenya. Nature 247: 344-348.
  2. Cerling, T. E., F. H. Brown, B. W. Cerling, G. H. Curtis and R. E. Drake, 1979. Preliminary correlations between the Koobi Fora and Shungura Formations, East Africa. Nature 279: 118-121.
  3. Curtis et al. 1975. Age of KBS Tuff in Koobi Fora Formation, East Rudolph, Kenya. Nature 258: 395-398.
  4. Drake, R. E., G. H. Curtis, T. E. Cerling, B. W. Cerling and J. Hampel, 1980. KBS Tuff dating and geochronology of tuffaceous sediments in the Koobi Fora and Shungura Formations, East Africa. Nature 283: 368-372.
  5. Fitch, F. J. and J. A. Miller. 1970. Radioisotopic age determinations of Lake Rudolf artefact site. Nature 226: 226-228.
  6. Fitch, F. J., P. J. Hooker and J. A. Miller. 1976. 40Ar/39Ar dating of the KBS Tuff in Koobi Fora Formation, East Rudolf, Kenya. Nature 263: 740-744.
  7. Fitch, F. J., J. A. Miller and J. G. Mitchell. 1996. Dating of the KBS Tuff and Homo rudolfensis. Journal of Human Evolution 30: 277-286.
  8. Gleadow, A. J. W. 1980. Fission track age of the KBS Tuff and associated hominid remains in northern Kenya. Nature 284: 225-230.
  9. Hillhouse, J. W., J. W. M. Ndombi, A. Cox and A. Brock. 1977. Additional results on paleomagnetic stratigraphy of the Koobi Fora Formation, east of Lake Turkana (Lake Rudolf), Kenya. Nature 265: 411-415.
  10. Hurford, A. J., A. J. W. Gleadow and C. W. Naeser. 1976. Fission-track dating of pumice from the KBS Tuff, East Rudolf, Kenya. Nature 263: 738-740.
  11. Lewin, Roger. 1987. Bones of Contention. New York: Simon and Schuster.
  12. Maglio, Vincent J. 1972. Vertebrate faunas and chronology of hominid-bearing sediments east of Lake Rudolf, Kenya. Nature 239: 379-385.
  13. McDougall, Ian, Robyn Maier, P. Sutherland-Hawkes and A. J. W. Gleadow. 1980. K-Ar age estimate for the KBS Tuff, East Turkana, Kenya. Nature 284: 230-234.
  14. McDougall, Ian. 1981. 40Ar/39Ar age spectra from the KBS Tuff, Koobi Fora Formation. Nature 294: 120-124.
  15. McDouball, Ian. 1985. K-Ar and 40Ar/39Ar dating of the hominid-bearing Pliocene-Pleistocene sequence at Koobi Fora, Lake Turkana, northern Kenya. Geological Society of America Bulletin 96: 159-175.
  16. White, T. D. and J. M. Harris. 1977. Suid evolution and correlations of African hominid localities. Science 198: 13-21.

Further Reading:

Hay, R. L. 1980. The KBS tuff controversy may be ended. Nature 284: 401.

Johanson, Donald and James Shreeve. 1989. Lucy's Child, New York: Avon, pp. 91-101.

Lewin, Roger. 1987. Bones of Contention. New York: Simon and Schuster, chaps. 9-10.
Previous Claim: CD020   |   List of Claims   |   Next Claim: CD101

created 2005-6-28