Measuring Time

Tree rings, Hillsborough forest. By Albert Bridge, with permission given on http://www.geograph.ie/photo/1506824
What is dendroarchaeology? You’ll know after reading about Ron Towner. He and his students study how people who lived long, long ago responded to changes in their environment. (Towner is the man in the blue cap in the photo at left.)

Tree rings are key to Towner's research because they show the passing of time. The calculations for this are not as simple as counting rings or equating each ring with a single year. Different types of trees vary in how fast they grow. Even one tree varies over its lifespan. A tree’s environment also affects its growth. This means that climate changes can be seen in tree rings. Combining social and physical sciences, Towner uses such patterns to date records of human responses to climate changes. For example, the traditional Navajo homeland in northwestern New Mexico was occupied during a period of high climatic variability. But the depopulation of the area in the 1750s was related to social pressures, not solely to climatic factors.
While much of Towner’s research has focused on Arizona, New Mexico, and Utah, he is expanding his locations. (See image below.) This is partly because one of the human behaviors that he studies is settlement patterns. Do people move when their environment becomes less inhabitable? Or do they stay and adapt to the new environment?