How relative dating works
The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality and the Law of Superposition, two important ideas used in relative dating.These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.A similar situation with igneous rocks occurs when xenoliths are found.These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix.Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another.Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating, archaeologists and geologists used relative dating to determine ages of materials.Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.The principle of Uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time.
The only disturbance that the layers experience is bioturbation, in which animals and/or plants move things in the layers.
The principle of faunal succession is based on the appearance of fossils in sedimentary rocks.
As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found.
Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic time eras.
Methods for relative dating were developed when geology first emerged as a natural science in the 18th century.The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative datin g' as observed in geology from the 17th century to the early 20th century.