Three laws of relative age dating
Many of the rock layers exposed in the walls of the Grand Canyon have not been disturbed by mountain building or other forms of deformation since they were originally laid down on Earth’s surface. Some older layers, however, have been tilted; the surface where these tilted layers are overlain by undeformed strata is called an angular unconformity.
These rocks are overlain by younger Paleozoic-age rocks.Stratigraphy and the Principles of Relative Dating Relative dating falls under the sub-discipline of geology known as stratigraphy.Stratigraphy is the science of rock strata, or layers.Layering occurs in sedimentary rocks as they accumulate through time, so rock layers hold the key to deciphering the succession of historical events in Earth’s past.The fundamental principles of stratigraphy are deceptively simple and easy to understand, but applying them to real rocks and fossils can be quite challenging.Here are the four fundamental principles of stratigraphy that form the foundation of our understanding of Earth’s history: Relative dating of rocks and fossils from an area is based on the Principle of Superposition, which enables scientists to put historical events in order.
Relating the succession of events in one region to those in another requires that the two areas be stratigraphically correlated.
Correlations can be made by tracing rock strata from one area to another by using the Principle of Lateral Continuity or by relating the fossils of the two areas using the Principle of Faunal Succession.
The Grand Canyon as an Example of the Principles of Stratigraphy The Grand Canyon spectacularly exposes rocks spanning hundreds of millions of years of Earth’s history.
This is an example of superposition: In a pile of sediment, the oldest deposits are at the bottom of the pile, underneath younger deposits.
Each major layer of sedimentary rock in the Grand Canyon contains different types of fossils.
The succession of fossils in the Grand Canyon is consistent everywhere in the canyon and is also similar to the succession of fossils in other parts of North America and on other continents.