Chaco

Lines of evidence
Trees are the oldest living things on Earth. They keep a detailed record of their life that can be read by anyone willing to do some detective work. Let’s take a look at one tree’s life story.

Go to File, Open Samples and open the image Chaco Slab .
This is a cross section of a wooden beam that was excavated from the Anasazi Indian ruins in Chaco Canyon, New Mexico. Tree trunks and branches show distinctive patterns of concentric rings. Each ring is a layer of wood produced on the outside of the tree, just under the bark, during the tree’s growing season. The red dots mark the growth rings every ten years, from 970 AD to 1020 AD.
In most trees, one growth ring is formed each year. During moist years, rapid growth builds thick rings, while dry years produce thinner rings. In this way, the rings tell us the life history of the tree and its environment.

Use the Magnifier Tool and click on the Moon Stack. Then grab a corner of the image so you can enlarge it and see everything at 200%.

Use the brightness and contrast controls under Image, Adjust, and the sharpen controls under Process to make the image to make the rings easier to see. (Your view should be similar to the image below.

1. Did the tree grow slowly or rapidly during its first few years? How can you tell?

2. How many years did the tree live?

The age of the tree is not all we can learn. The growth rings are shaped by factors like the soil, weather, insects, disease, and fire. Growth may also be affected by competition from other trees for sunlight, water, and nutrients. Ring patterns from both living and dead trees allow scientists to construct a history of climate and growing conditions going back thousands of years.

Reference

A thousand years ago in what is now the American Southwest, the Anasazi (a Navajo word meaning "ancient ones" or possibly "ancient enemies") built dramatic adobe dwellings, or pueblos. Chaco Canyon was the center of Anasazi civilization, its many large pueblos probably serving as administrative and ceremonial centers for a widespread population.

A Brief History of Chaco Culture National Historical Park

Chaco Road System:More than 400 miles of prehistoric roadway have been identified. This system connected Chaco to outlying communities and resource areas.

NASA:The Chaco Canyon Research Center had done aerial photography and a ground survey

Dendrochronology can determine absolute and relative dates of wood, its origin, and what climates were like in the past. Year-to-year variations in climate, especially rainfall amounts, are reflected in tree rings. A lot of rain in a given year causes thick rings, and little rainfall yields thin rings. In a given time period within a given area, the pattern of thick and thin rings is distinctive. It's like a fingerprint. All trees in the same area will show the same pattern of rings. By examining both living trees and archaeological remains of trees in a given area, scientists can document ring patterns hundreds or even thousands of years into the past.

Acknowledgments:

Activity developed bedaub Nead, Dzilth-Na-O-Dith-Hle Community School, Bloomfield, New Mexico, Center for Image Processing for Teaching

Images courtesy of Deb Nead; original tree samples courtesy of Laboratory of Tree-Ring Studies, University of Arizona.