The Grand Canyon is of relatively recent origin. The river started to erode the canyon about six million years ago.
Although the canyon itself is of relative recent origin, the rocks exposed in its walls are not. Most of the strata were originally deposited as marine sediment. The marine sediment indicates that the canyon used to be part of the shallow sea.
In a typical section of the canyon, nine separate rock layers can be seen. The topmost layer is a limestone, the Kaibab limestone. Below this layer is a thick deposit of Coconino sandstone, and below that a layer of Hermit shale, followed by the Supai formation. The fossils which were found in this formation suggested that these rocks were deposited in the Permian Period. Next comes a deposit of the Redwall limestone. The Redwall is 152 m (500 ft) thick. This layer belonged to the Mississippian Period. A thin layer of Temple Butte sandstone, beneath the Redwall, belonged to the Devonian Period. The next layers are the Muav limestone, the green Bright Angel shale, and the Tapeats sandstone, all belong to the Cambrian Period. Beneath these layers, at the bottom of the canyon, are the most ancient rocks of all, Precambrian schists and gneisses.
The geological time scale might help to see the age of certain rock layers in the Grand Canyon:
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