How a beam with no date gets one: tree rings and crossdating
30seconds
A beam from a ruined house has no date on it, but its rings do. Trees from the same region share the same wide and thin years, so a pattern of ring widths can be matched against a record whose years are already known.
Drag a mystery beam along a 160-year master record and watch the match score climb when the wiggles line up. Then shorten the beam to 10 rings and see why a short sample can be fooled, while a long one stands out clearly. This is crossdating, the trick that let tree rings date ruins, and now stretches back more than 12,000 years in Europe.
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