The Grand Canyon is a paradise for geologists, scientists who study the history and structure of Earth.
One way they do that is by examining rocks. Geologists can read rock colors and textures like a history book. Each level tells a different story.
Erosion has uncovered a mile of strata going up the canyon walls. Strata are layers of rock. Each layer was formed in a different time period, in which the ocean moved in, covered the land, and then retreated.
