In the last article of the December, 1929, issue of National Geographic Magazine, Andrew Ellicott Douglass, Sc.D., tells of his meticulous research to prove that analyzing tree rings can ascertain the age of wood and thereby date human structures, weather, and even weather conditions. "The Secret of the Southwest Solved by Talkative Tree Rings: Horizons of American History are Carried Back to A.D. 700 and a Calendar for 1,200 Years" is this chronicle.
Dr. Douglass was an astronomer studying sun spots. At that time, it was known that "there is a periodicity in their occurrence; they are most numerous at intervals of eleven years. As an aid in that astronomical investigation, I studied trees, for solar changes affect our weather, and weather in turn affects the trees in Arizona's dry climate, as elsewhere" (p. 742-743). He worked in the ruins of Indian civilizations in the States of Arizona, New Mexico, Colorado, and Utah.
We now take this research for granted but in 1929, it was a wonderful revelation. What I found more interesting in this article were the 'collateral' things Dr. Douglass learned in his journeys. He roamed many Indian ruins but also visited many current Indian villages and had to deal with the natives. How fascinating that he found many ancient logs, the larger ones, had been taken from ruins and transported great distances to serve in building newer structures! There is not an abundance of trees in the Southwest desert even now. What Dr. Douglass and his team did was to take core samples from the older logs and pieces of wood. Then they could analyze the tree rings.
The pine and Douglas fir trees were the most reliable source of information. "Every year the trees in our forests show the swing of Time's pendulum and put down a mark. They are chronographs, recording clocks, by which the succeeding seasons are set down through definite imprints. Every year each pine adds a layer of new wood over its entire living surface of trunk and branches. . . If every year were exactly the same, growth rings would tell the age of the tree and little more. Only in rare cases would they record exceptional events of any interest to us. But a tree is not a mechanical robot: it is a living thing, and its food supply and adventures through life all enter into its diary. A flash of lightning, a forest fire, insect pests or a falling neighbor may make strong impressions on its life and go into its diary" (p. 741).
Of course, if an Indian village was abandoned, such as that of the cliff dwellers in Colorado, the researchers could enter in and select the specimens that were the best. If they had heard of large or old logs in occupied dwellings, that was another story. Dr. Douglass had to convince the Indians to let him take a sample. Compounding the problem was communication: the Indians knew very few English words and Dr. Douglass and his team knew very little of their native languages. Gestures were frequently used.
In time, although most Indian males would cooperate with the scientific investigation, the women wanted compensation! Several times Dr. Douglass would have to fill a hole made by coring a log with turquoise "to prevent the lodgment of the 'spirit of decay' in the timber" (p. 753). The team found a log that was in continuous use for more than 500 years.
Dr. Douglass concluded that "The successful dating of the many ruins of the pueblo area that this research has made possible enables us now to correlate the increases of rainfall that permitted these villages to expand and the drought years that placed upon them the heavy hand of starvation" (p. 770).
As I was engaged in a small part of a research project at my hospital, one of more than 200 hospitals around the world doing the same research, in the two years before my retirement, I can fully appreciate all the care the Douglass team put into their work. Every part of the statistics had to be perfectly documented. The patient selection criteria for this sepsis (blood infection) study were extremely narrow. The National Geographic Society financed Dr. Douglass' study. A European medical company with a multi-billion dollar income is financing this particular research. It will be four years before we find out the results. Research takes patience!
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