# Overlapping dendrochronology to the rescue!

**URL:** <https://boards.straightdope.com/t/overlapping-dendrochronology-to-the-rescue/35380>\
**Category:** Cecil's Columns/Staff Reports\
**Created:** [October 2, 2000, 7:15pm UTC](https://boards.straightdope.com/t/overlapping-dendrochronology-to-the-rescue/35380 "2000-10-02T19:15:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\
**Post date:** [October 2, 2000, 7:15pm UTC](https://boards.straightdope.com/t/overlapping-dendrochronology-to-the-rescue/35380/1 "2000-10-02T19:15:17Z")

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In today’s Mailbag article, [http://www.straightdope.com/mailbag/mcarbon14.html](http://www.straightdope.com/mailbag/mcarbon14.html), Ken discusses measuring the Carbon-14 levels in tree rings (where the age is known) to figure out how high or low the background C-14 levels were for a given year, and thus to adjust radiocarbon dating tests on other substances:

> [@](#):
>
> carbon-dating within the past (say) thousand years or so can be adjusted fairly accurately. (There could still be local variation in the amounts of C-14, etc.) Carbon dating for much older samples has a greater margin of error, since we have have no way of knowing the variation in rate of C-14 absorption prior to the tree-ring era.

This assumes, however, that our ability to know when a given tree-ring was laid down goes only as far back as the oldest trees currently alive. Actually, there’s a way to go back much further than this. Two trees growing in the same forest will tend to have tree-ring patterns that are almost identical with each other, even if one of the trees is very old and the other is very young. It is possible to _line up_ the ring patterns from a recently-felled tree and a tree that died some long time ago, and thus determine precisely when that older tree died. We can then measure the C-14 levels in the rings of that much older tree, and go considerably farther back than we could if we had to rely on living trees.

This science of dating things from tree rings is called [dendrochronology](http://www.sonic.net/bristlecone/dendro.html).

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**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\
**Post date:** [October 3, 2000, 12:30pm UTC](https://boards.straightdope.com/t/overlapping-dendrochronology-to-the-rescue/35380/2 "2000-10-03T12:30:42Z")

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Dendrochonology, huh?

Well, they couldn’t call it tree-age, or it’d be confused with what they used to on the M_A_S\*H TV show.