Normal Curve: Tree Rings Tree-ring dates were used extensively in archaeological studies at Burnt Mesa Pueblo (Bandelier Archaeological Excavation Project: Summer 1989 Excavations at Burnt Mesa Pueblo, edited by Kohler, Washington State University Department of Anthropology). At one site on the mesa, tree-ring dates (for many samples) gave a mean date of m1 5 year 1272 with standard deviation s1 5 35 years. At a second, removed site, the treering dates gave a mean of m2 5 year 1122 with standard deviation s2 5 40 years. Assume that both sites had dates that were approximately normally distributed. In the fi rst area, an object was found and dated as x1 5 year 1250.

In the second area, another object was found and dated as x2 5 year 1234.

(a) Convert both x1 and x2 to z values, and locate both of these values under the standard normal curve of Figure 7-12.

(b) Interpretation Which of these two items is the more unusual as an archaeological fi nd in its location?