The Grand Canyon is made of sedimentary rock that contains fossils up to 1 billion years old. The most commonly found fossils in the Grand Canyon are sea organisms (crinoids, brachiopods, and sponges). However, several upper layers of rock contain terrestrial, or land-based, fossils, such as dragonfly wing impressions and the footprints of scorpions, centipedes, and reptiles. What do these fossils tell us about the evolution of the geosphere at the Grand Canyon?