Tree ring dating (dendrochronology)3 February 2006
Tree ring dating (dendrochronology) has been used in an attempt to extend the calibration of carbon-14 dating earlier than historical records allow, but this depends on temporal placement of fragments of wood (from long-dead trees) using carbon-14 dating.
Tree ring dating (dendrochronology) has been used in an attempt to extend the calibration of carbon-14 dating earlier than historical records allow. The oldest living trees, such as the Bristlecone Pines (Pinus longaeva) of the White Mountains of Eastern California, were dated in 1957 by counting tree rings at 4,723 years old. This would mean they pre-dated the Flood which occurred around 4,350 years ago, taking a straightforward approach to Biblical chronology.
However, when the interpretation of scientific data contradicts the true history of the world as revealed in the Bible, then it’s the interpretation of the data that is at fault. It’s important to remember that we have limited data, and new discoveries have often overturned previous ‘hard facts’.
Recent research on seasonal effects on tree rings in other trees in the same genus, the plantation pine Pinus radiata, has revealed that up to five rings per year can be produced and extra rings are often indistinguishable, even under the microscope, from annual rings. As a tree physiologist I would say that evidence of false rings in any woody tree species would cast doubt on claims that any particular species has never in the past produced false rings. Evidence from within the same genus surely counts much more strongly against such a notion. Creationists have shown that the biblical kind is usually larger than the ‘species’ and in many cases even larger than the ’genus’—see my article Ligers and wholphins? What next?.
Considering that the immediate post-Flood world would have been wetter with less contrasting seasons until the Ice Age waned (see Q&A: Ice Age), many extra growth rings would have been produced in the Bristlecone pines (even though extra rings are not produced today because of the seasonal extremes). Taking this into account would bring the age of the oldest living Bristlecone Pine into the post-Flood era.
Claimed older tree ring chronologies depend on the cross-matching of tree ring patterns of pieces of dead wood found near living trees. This procedure depends on temporal placement of fragments of wood using carbon-14 (14C) dating, assuming straight-line extrapolation backwards of the carbon dating. Having placed the fragment of wood approximately using the 14C data, a matching tree-ring pattern is sought with wood that has a part with overlapping 14C age and that also extends to a younger age. A tree ring pattern that matches is found close to where the carbon ‘dates’ are the same. And so the tree-ring sequence is extended from the living trees backwards.
Now superficially this sounds fairly reasonable. However, it is a circular process. It assumes that it is approximately correct to linearly extrapolate the carbon ‘clock’ backwards. There are good reasons for doubting this. The closer one gets back to the Flood the more inaccurate the linear extrapolation of the carbon ‘clock’ would become, perhaps radically so. Conventional carbon-14 dating assumes that the system has been in equilibrium for tens or hundreds of thousands of years, and that 14C is thoroughly mixed in the atmosphere. However, the Flood buried large quantities of organic matter containing the common carbon isotope, 12C, so the 14C/12C ratio would rise after the Flood, because 14C is produced from nitrogen, not carbon. These factors mean that early post-Flood wood would look older than it really is and the ‘carbon clock’ is not linear in this period (see The Creation Answers Book, chapter 4).
The biggest problem with the process is that ring patterns are not unique. There are many points in a given sequence where a sequence from a new piece of wood matches well (note that even two trees growing next to each other will not have identical growth ring patterns). Yamaguchi1 recognized that ring pattern matches are not unique. The best match (using statistical tests) is often rejected in favour of a less exact match because the best match is deemed to be ‘incorrect’ (particularly if it is too far away from the carbon-14 ‘age’). So the carbon ‘date’ is used to constrain just which match is acceptable. Consequently, the calibration is a circular process and the tree ring chronology extension is also a circular process that is dependent on assumptions about the carbon dating system.2
The extended tree ring chronologies are far from absolute, in spite of the popular hype. To illustrate this we only have to consider the publication and subsequent withdrawal of two European tree-ring chronologies. According to David Rohl,3 the Sweet Track chronology from Southwest England was ‘re-measured’ when it did not agree with the published dendrochronology from Northern Ireland (Belfast). Also, the construction of a detailed sequence from southern Germany was abandoned in deference to the Belfast chronology, even though the authors of the German study had been confident of its accuracy until the Belfast one was published. It is clear that dendrochronology is not a clear-cut, objective dating method despite the extravagant claims of some of its advocates.
Extended tree ring chronology is not an independent confirmation/calibration of carbon dating earlier than historically validated dates, as has been claimed.
- Yamaguchi, D.K., Interpretation of cross-correlation between tree-ring series. Tree Ring Bulletin 46:47–54, 1986. Return to text.
- Newgrosh, B., Living with radiocarbon dates: a response to Mike Baillie. Journal of the Ancient Chronology Forum 5:59–67, 1992. Return to text.
- Rohl, David, A Test of Time, Arrow Books, London, Appendix C, 1996. Return to text.