As you look at the sedimentary rocks at the Grand Canyon's rim, the top layers of visible rock are the youngest. In this video segment adapted from NOVA, a scientist explains what we know about the changing conditions in this location and the kinds of life they supported. The canyon's top layer, the Kaibab formation, records deposits laid down at the bottom of a shallow sea. The Coconino sandstone formation below it indicates that these watery conditions were preceded by much drier ones. This video is available in both English and Spanish audio, along with corresponding closed captions.