Geologic age dating methods
Inclusions: Inclusions, which are fragments of older rock within a younger igneous rock or coarse-grained sedimentary rock, also facilitate relative dating.Inclusions are useful at contacts with igneous rock bodies where magma moving upward through the crust has dislodged and engulfed pieces of the older surrounding rock.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.
Indexing Absolute-age methods are entered in the standard form most commonly found in the geologic literature.
These notes should be read along with the instructions under the individual terms in the body of the Thesaurus.
Age-dating methods Age-dating methods are divided into two major groups: absolute-age and relative-age methods.
If a geologist claims to be 45 years old, that is an absolute age.
Superposition: The most basic concept used in relative dating is the law of superposition.