Earth Notes
11:40 am
Wed June 3, 2009

Earth Notes - The Missing Rings

Flagstaff, AZ – Earth Notes: The Missing Rings

Archaeologists have an insatiable desire to tell time. They use every tool they can to get at the ages of artifacts, sites, and entire cultures. One technique that has proven extremely valuable, especially in the Southwest, is tree-ring dating.

Astronomer A.E. Douglass pioneered the technique in the early 20th century by studying distinctive annual growth rings in the wood of ponderosa pine trees around Flagstaff. Encouraged by archaeologists, he began compiling a master tree-ring record based on the timbers used in the construction of ancient pueblos.

But by the late 1920s Douglass was stuck. He hadn't been able to date any rings to the middle of the 13th century. That gap in the record made it impossible to link modern and prehistoric tree-ring records.

On June 22, 1929, young archaeologist Emil Haury (Em-EEL HOW-ree) helped unearth a good-sized timber from a ruin near Show Low, Arizona. Later, Haury and coworkers waited around a gasoline lamp while Douglass pored over the charred beam, assessing its age.

Soon Douglass announced, "I think we have it. . . . Beam HH-39 has established the bridge." Its sequence of rings included the 13th century, and allowed him to craft a master tree-ring sequence extending continuously back to about A.D. 700.

That, in turn, allowed archaeologists to confidently assign ages to significant southwestern cultural sites, including structures at Chaco Canyon, Mesa Verde, and Navajo National Monument.

The unforgettable experience, Haury later wrote, "set the chronological house in order for the Southwestern United States."

-Rose Houk