Thursday, May 1, 2014

Dendrochronology: An argument against a young earth

Diagram depicting the process of crossdating.  Image source.

The Problem

As a young-earth creationist, I believe that the earth is approximately 6000 years old.  Obviously, many people do not agree with me, so it is apparent that the case is not clear-cut.  Over the last week, I have been investigating the claims of dendrochronology, which is often cited by others to demonstrate that the earth must be more than 6000 years old.  Quite frankly, I do not have an answer to it at the moment.  It seems straightforward enough to have captured my attention for the last week, but not quite enough to cause me to accept a 4.6 billion-year age for the earth.

Background

Dendrochronology, generally speaking, is the science of using tree rings to date events.  As most people know, trees grow annual rings in the wood of their trunks, giving wood its characteristic appearance.  These rings form because the tree produces large cells with thinner walls during the spring growing season, and smaller cells with thicker walls at the end of summer, resulting in alternating light and dark bands that develop outward from the center.  So, to determine the age of a tree, one can simply count the number of rings in a cross-section of the trunk.  According to Rocky Mountain Tree-Ring Research, the oldest tree dated by direct ring-counting was a sequoia in northern California that was 2200 years old when it died (older ages have been claimed for other trees, but those were measured using carbon dating or crossdating, described below).

Dendrochronologists, however, look past the mere number of rings.  Environmental factors, such as fire, drought, flooding, and infestation can affect the width of the rings, so such events can be dated using dendrochronology.  Of course, the rings are only affected if the tree is alive and growing at the time, and it is very difficult to count the rings of a living tree without killing it, which scientists try to avoid.  To get around these obstacles, dendrochronologists have developed an alternative means of tree-ring dating called crossdating.

Crossdating

Crossdating relies on the fact that the width of the light rings in a tree reflect the conditions of the annual growing season.  Under good conditions, such as warm temperature, abundant (but not too abundant!) rainfall, and plentiful nutrients, trees grow quickly, resulting in thick rings.  Periods of drought or poor soil will result in thin rings.  Crossdating attempts to take advantage of these annual variations to match the rings of one tree to those of another.  Given several trees with overlapping lifetimes, a dendrochronologist could line up the rings and construct a timeline longer than the lifetime of any individual tree.  If one of those trees is still alive, then the timeline can be anchored to a known date.  Also, because the full range of the tree's age isn't necessarily needed, scientists can simply take a core of the living tree rather than cutting it down.

What does this have to do with the age of the earth?  Using crossdating, scientists have claimed to build a timeline stretching back 11,000 years using living and dead oak and pine trees from Germany.  Obviously, this does not fit well within the creationist timeline of 6000 years, particularly with a worldwide catastrophic flood 4400 years ago.  Yet, the constructed dendrochronology appears to be quite robust.  Every point on the timeline is corroborated by multiple samples, sometimes numbering in the hundreds.  This effectively discounts any possibility of faulty counting or anomalously missing/extra rings throwing off the chronology.  If there was somehow an acceleration of ring growth after the Flood, it would have to have been extreme and cosmopolitan to produce such results, and I find this unlikely.

If there is a flaw in the crossdating technique, I believe it to be in the method by which the rings are actually matched.  Scientists can't simply compare two pictures of wood and slide them past each other until all of the rings line up.  Trees grow at different rates, so even if the relative annual growth rates were affected similarly, the overall growth rate would make direct matches impossible.  Several methods are used to match ring sequences, but the two most prominent appear to be skeleton plotting and statistical matching.


Skeleton plotting

A sample skeleton plot.  Credit: University of Arizona.
Skeleton plotting seems unusually subjective to me.  In this method, a person draws marks on graph paper (or digitally) according to the width of the rings.  Long marks are used for thin rings, and short marks are used for thick rings (I don't know why).  The rings don't appear to be measured; their relative size is important here.  Once two samples have been graphed out, the researcher lines up the plots so that a set of lines mirrors each other.  The more overlap, the better.  Strangely, all the examples I've seen of this method don't actually graph every ring.  They appear to only focus on the unusually wide or thin ones.  I don't find skeleton plotting to be particularly rigorous at all, as it has the potential to introduce quite a bit of user error and interpretation.  You can actually try some skeleton plotting yourself with this tutorial from the University of Arizona.


Statistical matching

The German study I referenced earlier used a different and more objective method to match its samples.  It cites an old computer program, written in the FORTRAN computer language, specifically written to compare tree rings.  Ring width measurements from two samples are read by the program, which overlaps them in every possible configuration, performing a statistical t-test at each point.  The t-test compares the two sets of values as they are aligned and returns a number t that reflects the likelihood that any correlation between the sets could have been produced randomly.  If t=0, the sets almost certainly have nothing to do with each other.  If t>3, they are likely related.  In the example given in the documentation of the program, only one alignment position returned a t value above 3 (t=5.29) out of 250 possible alignments.  It is therefore extremely likely that the one particular alignment is the correct one.  Unfortunately, the German study does not provide any raw data, but it cites t values ranging from 3.6 to 10.9.

I could not find any reference to how the rings were measured before being entered into the program.  If the program reads skeleton plots, then this technique has the same shortcomings as that method.  If it reads direct measurements, then any flaws are more subtle.  One possible flaw is that the t-test assumes the data in each set falls on a normal curve, which would imply that the cause of the data is completely random.  In this case, the cause is primarily climate.  Though climate may be hard to predict, it may not be truly random.  I suspect that repeating climate patterns may throw off the t-test, possibly resulting in misalignments.  This is difficult to prove, however, and it is a bit of a long shot given the great number of samples used in the study.


Conclusion

As I said at the beginning, I have no satisfying answer to this problem.  I have been pondering the facts and will continue to investigate this issue, but for now I leave you with all I know.  I didn't think it fair to put off writing about this until I could come up with a solution.  My aim is to be honest and informative, not to show off how much I know and can answer.  Nevertheless, God and His Word stand fast and true.

3 comments:

  1. Do you think a possibility is that the 11,000 year old trees were created with annual rings already there? Or the first trees were thick, but only had an external bark and no rings. Also, any change multiple rings formed in 1 year?

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    1. I would find it strange if trees were created with thousands of rings. Granted, they were fully grown and mature when they were created, but rings imply a history. On the other hand, the rings may be a structural necessity and were therefore present in the original trees, but they still shouldn't correlate in the offset manner they are claimed to do. Also, because of the Flood, there shouldn't be a continuous timeline extending to Creation anyway.

      There have been studies that have demonstrated that multiple rings can form in extreme conditions, particularly in Bristlecone Pines. To explain the current circumstances, however, these extreme conditions would have had to have lasted for thousands of years to produce so many extra rings. I find it more likely that the fault lies in the statistical methods of matching. It's still worth investigating, though.

      Thanks for your response!

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  2. Reviving an old thread here...
    I suspect the link below would be of interest to you. It doesn't do too terribly much to mitigate the problem of single trees dating beyond the flood other than to point out that seasons may have been far less defined after the flood and hence allowed for multiple tree rings in a single year.
    Regards crossdating I find the below link to be a very useful and strong in its arguments against the supposed reliability of crossdating. Specifically about 1/2 to 2/3 of the way into the article.
    Enjoy!
    http://www2.asa3.org/archive/asa/199905/0017.html

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