5.4: What is dendrochronology? (Creation versus Evolution)
Description
This article is from the Scientific Skepticism FAQ, by Paul Johnson Paul@treetop.demon.co.uk with numerous contributions by others.
5.4: What is dendrochronology? (Creation versus Evolution)
The science of dating wood by a study of annual rings.
[These figures and references come from a longer summary e-mailed to me
by <whheydt@pbhya.PacBell.com>. Any mistakes are mine. PAJ]
Everyone knows that when you cut down a tree the cut surface shows a
series of concentric rings, and that one of these rings is added each
year as the tree grows. The lighter part of the ring is the summer
growth and the darker part is the winter growth. Hence you can date a
tree by counting the rings.
But the rings are not evenly spaced. Some rings are wider than
others. These correspond to good and poor growing seasons. So if you
have a piece of wood cut down a few thousand years ago, you can date
it by comparing the pattern of rings in your sample to known patterns
in recently cut trees (Bristlecone pines exist which are over 4600
years old, and core samples allow ring counting without killing the
tree).
Now for the clever bit. The tree from which your sample came may have
been old before any trees now alive were even saplings. So you can
extend the known pattern of rings back even further, and hence date
samples of wood which are even older. By lining up samples of wood in
this way, dendrochronologists have been able to produce a continuous
pattern of rings going back around 9,900 years. This easily refutes
the chronology of Bishop Usher, who calculated from dates and ages
given in the Bible that the Earth was created in 4004 BC.
Dendrochronology is also valuable in providing calibration data for
C14 and other isotope dating methods. See the previous question for
more details.
References:
"Dendrochronology of the Bristlecone Pine....."
by C. W. Ferguson, 1970. Published in a book called
"Radiocarbon Variations and Absolute Chronology"
This takes the record back 7484 years. More recently there is
Bernd Becker, Bernd Kromer & Peter Timborn
"A stable-isotope tree-ring timescale of the Late
Glacial/Holocene boundary"
Nature 353 (1991) pp. 647-649
The authors have "established a 9,928 year absolute dated
dendrochronological record of Holocene oak." Actually, their timescale goes
even further back, because by overlap with a pine tree sequence they date
the end of the Late Glacial at a minimum age op 10,970 BP.
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