Follow along with host Kirk Johnson as he explores the layers of rock that make up the Grand Canyon, in this video from NOVA: Making North America: Origins. Many geologists think that the Grand Canyon is the best place in the world. Its exposed rock layers allow them to see hundreds of millions of years back in time, revealing a story about what the surface was like as each rock layer formed. By analyzing the rock, mineral, and fossil contents of the layers, scientists know that what is today the North American continent was covered by desert sands, shallow seas, and more in its distant past.