TELLING TIME AT GRAND CANYON NATIONAL PARK: A COMPILATION OF NUMERIC AGES FOR ROCKS EXPOSED IN GRAND CANYON

With one of the best exposures of the rock record on the continent, Grand Canyon is an ideal place to gain a sense of geologic or “deep” time. Telling geologic time is an important part of Grand Canyon National Park's interpretive efforts as the canyon's story cannot be told without the perspective of geologic time. However, how geologists determine the age of rocks is a mystery to many visitors and park staff without a background in Earth science. The technical literature is not an easy place for lay people to discern the age of rocks in an understandable format.

Interpreters should use numeric ages when communicating geology to the public as they serve as important translations of geologic ages. We reviewed the technical literature and consulted with researchers to compile the “best” ages of Grand Canyon rocks (http://www2.nature.nps.gov/geology/parks/grca/age/). By “best” we mean the most accurate and precise ages, given the parameters of dating techniques and available information from the rock record. The age chart was published in a variety of general articles that also explained how geologists tell time and why these dates are important. The primary audiences for this work were interpreters (rangers, guides, authors, and publishers) and resource managers. The goal was to develop a single list of numeric ages that users could apply consistently, thereby facilitating comprehension of the geologic history of Grand Canyon. As a result of our project, the ages given for Grand Canyon rocks are already more consistent in interpretive media, park documents, and popular publications.

This project is a good example of collaboration among scientists, resource managers, and interpreters. Interpreters have a significant need for consistent, reliable ages for Grand Canyon rocks, and for a better understanding of geologic dating techniques. This compilation and accompanying information about dating methods can help interpreters address the sociopolitical controversy regarding deep time and evolution. Resource managers benefited by having an internally consistent and scientifically credible time scale to use. Finally, working directly with researchers has fostered communication and credibility among park interpreters, resource managers, and the academic community.