This program shows the process of sedimentation, which has preserved those life forms extant at the time the rock was formed and—most strikingly where the Colorado River has cut through the Grand Canyon—exposes a veritable history of life on earth; presents the stratified evidence that simple organisms populated the earth first, followed by increasingly complex forms; demonstrates modern techniques for dating rock samples; and explains why fossils provide important evidence of the theory of evolution. After viewing the program, students should understand the mechanisms that made possible the Colorado River rock record, where the oldest and youngest rocks are and why, how the absolute age of rocks is determined, and the nature and extent of the record provided by rocks. (20 minutes)