My favorite science experience was certainly the earliest I can remember. I grew up on the Navajo Indian Reservation in northern Arizona. When I was in second grade, I rode a horse out to Keet Seel Ruin to visit a dendrochronologist named Jeff Dean. He was using tree rings to find the ages of the timbers used for construction of the village. Keet Seel is a very large and well-preserved cliff dwelling built by the Ancestral Pueblo people in the13th century (1200s). Using cross dating, Dr. Dean documented the dates when people cut the trees used in their dwellings. Cross-dating is a method used to match tree-ring patterns in different trees. Cross-dating enables dendrochronologists to go back in time. This is what tree ring scientists do all the time, not only to study archaeology, but also to look at past rainfall and many other things that influence tree growth.