How Do Trees Record Time?
ES2905  A Crossdating Simulation

In 1929, Andrew Douglass used tree rings to accurately date archaeological ruins in the southwestern United States. By combining data from tree ring samples at a number of locations, he was able to build a chronology, or timeline, that he then used for dating other samples. To understand how tree rings can be used to build a timeline, you will simulate this process. You will determine the ages of two samples of wood found in ancient Native American cliff dwellings.

Instead of working with entire cross sections of trees, dendrochronologists (tree-ring researchers) often use long, slender cores extracted from trees by a hollow tool. The diagram below shows two cores from different trees in the same area. The banding patterns on the cores correspond to a close-up view of the cross section of a tree. The center ring of each tree is on the left.

  !   Examine the cores below. Look carefully at the "wet" and "dry" years indicated by the width of rings in both cores.

Carla McAuliffe, TERC

4. How old is this tree? (Core 1)

5. How old is this tree? (Core 2)

6. How do the banding patterns of the two cores compare?


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