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.