Blame sheep for screwing up tree-ring dating

Illustration for article titled Blame sheep for screwing up tree-ring dating

Dating objects based on tree rings — dendrochronology if you want to get technical — requires a fairly advanced understanding of how the environment interacts with the trees in order to be accurate. It's fairly common for scientists to make inferences about ancient climate based on the condition of tree rings at certain points in time. Except now it turns out that roving animals may have more to do with tree ring formation than the weather.

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New research published in Functional Ecology has shown that sheep have more of an impact on tree rings than the climate. Over a period of nine years, scientists in Norway and Scotland allowed sheep to graze around one set of birch trees, and protected another. Nine summers later, they chopped down the trees, and analyzed how thick the rings were.

Contrary to the accepted belief, the climate wasn't the biggest influence on the tree ring thickness. While the ambient temperature still altered how large the ring was, grazing herbivores slimmed it down the most.

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While this doesn't invalidate analyzing ancient climates through tree rings, it does make it more complicated, as you need to attempt to take into account numbers and types of domestic animals that may have affected the outcome.

Photo by Matt Huffman

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DISCUSSION

This is the unknowable problem with every "dating method".

There is always an agreed-upon 'Constant' that is assumed to decay/accumulate/remain the same throughout the examined time period.

What if conditions on Earth were somehow different in the past in a way that would affect the Constant?

For instance, with C14 dating: It is assumed to accumulate in an organism at today's rate. What if during some period in the past there was an entirely different condition of some sort that changed the percentage of C14 available? If the atmosphere had a different structure that prevented cosmic radiation from reaching the biosphere at current rates? Artifacts from such a period would appear to be far older than they actually were, since their low C14 level would be interpreted incorrectly.

In what other ways might assumptions of Science be broken?