Relative dating concept
For example, shells, wood, and other material found in the shoreline deposits of Utah’s prehistoric Lake Bonneville have yielded absolute dates using this method.
These distinct shorelines also make excellent relative dating tools.
Geologists generally know the age of a rock by determining the age of the group of rocks, or formation, that it is found in.
The age of formations is marked on a geologic calendar known as the geologic time scale.
Development of the geologic time scale and dating of formations and rocks relies upon two fundamentally different ways of telling time: relative and absolute.
Relative dating places events or rocks in their chronologic sequence or order of occurrence.
Half-lives of these isotopes and the parent-to-daughter ratio in a given rock sample can be measured, then a relatively simple calculation yields the absolute (radiometric) date at which the parent began to decay, i.e., the age of the rock.
Of the three basic rock types, igneous rocks are most suited for radiometric dating.
This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.
Many sections of the Wasatch fault disturb or crosscut the Provo shoreline, showing that faulting occurred after the lake dropped below this shoreline which formed about 13,500 years ago.
As this example illustrates determining the age of a geologic feature or rock requires the use of both absolute and relative dating techniques.
Using these methods, the scientist determines a date range for when an event took place rather than where it fits in the overall record. The techniques scientist need for absolute dating did not become available until the later half of the 20th century.
Absolute dating uses clues, such as the emperor's face on a coin, to date an artifact.