Sunday, August 19, 2007

The Trees that Rewrote History

Back from a wonderful two weeks in the Eastern Sierras and the high country of Yosemite! My first stop on vacation was a day trip into the White Mountains of California, home of the "trees that rewrote history". This was a fascinating venture into the world of the Bristlecone Pine Forest and the science of dendrochronology. The Bristlecone Pine Forest in this region is home to the world's oldest known living tree which is 4,776 years old. However in this region deadwood has been dated to be as old as 11,400 years old and the scientific community is continuing to explore the deadwood. in this area. Any other place in the world wood 3,000 years old would be an incredible find but in this location it has to be at least 7,000 years old to create any ripple of excitement.

The whole story of dendrochronology and the rangers explanation of the process of dating trees was captivating. It was amazing how low tech the procedure is and how much of the work like counting rings is done essentially by hand. I was also intrigued by the way that these trees have changed our understanding of history. The ranger, Christine, explained how through dendrochronology they have been able to date some of the Native American ruins by taking core sampling's from the wood used in the lintels. She also explained how the bristlecone helped to calibrate radio carbon dating and caused a shift in some of the dates assigned to historic events and locations like the great pyramids. I tried to record her talk as a podcast but I did not get a good quality audio. Therefore I have had to rely on bits an pieces to provided this abbreviated explanation. It was previously assumed that Radiocarbon was created at a constant rate and so by measuring the carbon present an object could be dated. With the discovery of the ancient bristlecone it was possible to count the rings and sample the level of radiocarbon present and thus calibrate the dating more accurately. Generally speaking it was discovered that in many instances radio carbon dating was too "young" and it was established that the level of radiocarbon created is not constant overtime but rather it is effected by a number of factors. Thus the bristlecone pines became known as the trees that rewrote history.

Another part of all of this that appealed to me was the sense of dendrochronology as a puzzle waiting to be solved. The ranger spoke about how they establish a timeline and look for overlapping patterns to establish a fixed timeline. If you know the date of one sample you can count backwards to date the others. This is all explained and illustrated much more eloquently, as in this example at the right, on the website for the Ancient Bristlecone Pine.

What a great opportunity to walk among these ancient trees and oh how painless learning is when we are choosing our path and involved in real work with others who are passionate about what they are doing. Truly both the ranger and scientist I spoke with were so passionate and animated that you were drawn into their world even if just for a short while.

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