The Grand Canyon's stratified rock features layers from the Cambrian, Mississippian and Permian eras.
The Earth's rocky layers formed over millions of years as sediments and soils filled in existing lakes, rock beds and earth. The Cambrian, Mississippian and Permian layers all developed during the Paleozoic Era, an important period in the growth and diversification of the planet's animal life. Where the layers are visible, they generally appear stacked in chronological order, though some renowned landmarks feature unconformities, or mismatched strata.
Cambrian Layer
This layer formed between 540 million and 490 million years ago, from sediment lining lakebeds. It consists of limestone, shale and sandstone. Some Cambrian specimens have observable ripple marks formed from the waves of ancient oceans. The Cambrian layer harbors diverse fossils thanks to its rapid proliferation in life forms, including crustaceans, spiders and insects. Remains of soft-bodied worms have been found in Cambrian layers in Canada and Greenland, and a major Chinese fossil bed held 530 million-year-old fossils belonging to tiny, jawless fish --- the oldest known vertebrates with contemporary relatives.
Mississippian Layer
Laid 354 million to 323 million years ago, this layer features sandstone, shale, limestone and clay on top of a coal bed formed from dead plants and marine sediments. Fossil finds from the Mississippian layer show corals, snails, fish, amphibians, sharks, clams and tree ferns. The era saw a massive lake cover much of North America, from northern Canada down to Florida. Much of the lake was shallow, and hospitable to the development of new life forms.
Permian Layer
Rapid and drastic changes in climate shaped this layer, formed 290 million to 248 million years ago. The Permian period saw the formation of Pangea, a supercontinent from which many of today's continents broke away. Hardy plants and animals that could survive harsh cold, intense heat and drought conditions emerged in this period. The layer's remnants consist of sandstone and shale, with small amounts of limestone. The close of the Permian period brought a mass extinction, with millions of fossils resulting from the die-off. Reptiles, beetles, bugs, fish and conifer trees all left behind remnants in the Permian layer.
Where to See the Layers
The United States is home to several landmarks that allow visitors to see the Cambrian, Mississippian and Permian layers together. The Grand Canyon, with its exposed rock and lack of development, offers some of the best examples of stratified earth, including the Cambrian, Mississippian and Permian layers. In some areas, the layers rest on top of each other chronologically. In other spots, tectonic activity or erosion forced older rock over newer layers, giving rise to unconformities, or time gaps, in the layers. Other areas with both chronologically stacked layers and unconformities include Lake Mead National Recreation Area in Nevada and Grand Teton National Park in Wyoming.
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