The spectacular geology at Grand Canyon provides an unparalled opportunity to introduce literally millions of visitors to Earth science in the broadest possible sense. In cooperation with the National Park Service and the National Science Foundation, we are developing a geologic exhibit and education program entitled: “The Trail of Time”. The core project is a 2 km-long trail at the edge of the Canyon on the south rim, scaled so that one meter represents one million years of Earth history.  The primary ‘exhibit’ is the Trail itself, focusing on the rocks exposed in the Grand Canyon and the southwestern U.S. The Trail will extend east from Yavapai Point, towards the Kaibab Trailhead. Along the Trail, visitors will see the rocks and relationships which shape our current understanding of the Canyon’s history, beginning with the formation of the continent ~ 2 Ga and ending with geosocietal issues surrounding the interaction of humans with the Canyon.  Near the Canyon View Information Plaza (CVIP) and Yavapai Observation Station, the exhibit will also include: 1) “What is a Million Trail”, which explores the magnitude of this number-the approximate number of years that pass with each step of the Trail; and 2) “Trail of Canyon Cutting”, which employs a different scaling factor, and uses the 100-year-long debate about Canyon incision to highlight the scientific method. The goal is for visitors to walk through both the geology and the geologic history of the Canyon, and to gain an understanding of how geologic time is related to the rock record, some fundamentals of Earth processes, and the vitality of the scientific method. The Trail of Time is designed to reach all levels of visitors, from children to other scientists. We will use new information technologies to organize information into interactive, spatially oriented databases, provide digital maps and images of the Grand Canyon, and provide a venue for long-term GIS-based data integration and management. Planning moves forward with the assistance of an advisory board composed of museum & exhibit design specialists, K-12 teachers, and additional scientists. We seek collaboration with other Parks and other geoscience education efforts; it is our hope that this effort will serve as a model for geoscience interpretation in other National Parks.