On the Colorado Plateau, the rocks weren’t altered significantly they were instead lifted high and flat. The rocks that comprise the Rocky Mountains, for example, were dramatically crunched and deformed during their uplift. With uplift, geologists generally expect to see deformation of rocks. The way in which the uplift of the Colorado Plateau occurred is puzzling. The action of plate tectonics lifted the rocks high and flat, creating a plateau through which the Colorado River could cut down. Uplift of the Colorado Plateau was a key step in the eventual formation of Grand Canyon. How did these sea floor rocks attain such high elevations? Yet today, at the top of the Colorado Plateau, the Kaibab Limestone is found at elevations up to 9,000 feet. The Kaibab Limestone, the uppermost layer of rock at Grand Canyon, was formed at the bottom of the ocean. The start of the South Kaibab trail shows an abundant display of Kaibab stone. If rock layers appear tilted, that is due to some geologic event that occurred after the rocks were originally deposited. This means that all the rock layers were laid horizontally. In geology, this is referred to as the principle of superposition, meaning rocks on the top are generally younger than rocks below them.Īnother important principle is the principle of original horizontality. That means that the bottom layer was formed first, and every subsequent layer was formed later, with the youngest rocks on the top. It shows the rock layers with the oldest on the bottom, and the youngest on the top. To look at rock layers, geologists use a diagram called a stratigraphic column. Then, layer upon layer of sedimentary rocks were laid on top of these basement rocks. The story begins about 2 billion years ago when igneous and metamorphic rocks were formed. The story of how Grand Canyon came to be begins with the formation of the layers and layers of rock that the canyon winds through. By comparison of overlapping sequences, it is possible to build up a continuous record of faunas or floras that have progressively more in common with present-day life-forms as the top of the sequence is approached.Horizontal striations can be found in the walls of the majority of the canyon. In such sequences of layers in different places, the same, or similar, fossil floras or faunas occur in the identical order. It is often observed that each layer in such a sequence contains fossils that are distinct from those of the layers that are above and below it. In some places, such as the Grand Canyon in Arizona, it is possible to recognize a great thickness of nearly horizontal strata representing the deposition of sediment on the seafloor over many hundreds of millions of years. A brief treatment of the fossil record follows. Occasionally the original material is simply removed while nothing is deposited in its place in this case, all that remains is a mould of the shape of the plant or animal. In a few cases the original substance of the hard parts of the organism is preserved, but more often the original components have been replaced by minerals deposited from water seeping through the rock. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!įossil record, history of life as documented by fossils, the remains or imprints of organisms from earlier geological periods preserved in sedimentary rock.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians. COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.
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