Nature's Time Capsules The analysis of middens is emerging as a distinct scientific specialty. Its handful of practitioners have already published a 472-page tome on the subject (Packrat Middens; University of Arizona) and have considered naming the specialty paleonidology, which roughly translated means "study of old nests." By whatever name, the investigation of middens is paying off with a host of new insights about the past. Using midden evidence of tree growth and distribution in the Mojave Desert, botanist W. Geoffrey Spaulding of the University of Washington determined that average desert temperatures during the height of the last Ice Age, about 18,000 years ago, were 60(110F) colder than they are today. In a midden study covering 11,000years of vegetation change in New Mexico's Chaco Canyon, Julio Betancourt of the U.S. Geological Survey and Thomas Van Devender of the Arizona-Sonora Desert museum found evidence that could explain why a once thriving Anasazi Indian community was abandoned 800 years ago. Simply stated, the Indians eventually used all the surrounding pine trees for their dwellings and firewood, depleting the woodland and eroding the farmland vital to the tribe's survival. Middens made by hyraxes--rodents found in Africa and the Middle East--have provided similar evidence that human clearing of surrounding forests and shrubbery led to the sudden collapse in A.D. 900 of the ancient metropolis of Petra, in what is now Jordan.