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. The story begins about 2 billion years ago when igneous and metamorphic rocks were formed. Then, layer upon layer of sedimentary rocks were laid on top of these basement rocks.
To look at rock layers, geologists use a diagram called a stratigraphic column. It shows the rock layers with the oldest on the bottom, and the youngest on the top. That means that the bottom layer was formed first, and every subsequent layer was formed later, with the youngest rocks on the top.
In geology, this is referred to as the principle of superposition, meaning rocks on the top are generally younger than rocks below them.
Another important principle is the principle of original horizontality. This means that all the rock layers were laid horizontally. If rock layers appear tilted, that is due to some geologic event that occurred after the rocks were originally deposited.
Credit : National Park Service
Picture Credit : Google
