When erosion takes place, sedimentation—the deposition of material—also eventually occurs. Through time, sediments are buried by more sediments and the material hardens into rock. This rock is eventually exposed (through erosion, uplift, and/or faulting), and the cycle repeats itself. Sedimentation and erosion are “reshapers” and “refiners” of the landscape—and they also expose Yellowstone’s past life as seen in fossils like the petrified trees.