Radiometric dating rock layers


Metamorphic rocks may also be radiometrically dated.However, radiometric dating generally yields the age of metamorphism, not the age of the original rock.Relative dating techniques provide geologists abundant evidence of the incredible vastness of geologic time and ancient age of many rocks and formations.However, in order to place absolute dates on the relative time scale, other dating methods must be considered.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.Particularly useful are index fossils, geographically widespread fossils that evolved rapidly through time.Crosscutting Relationships: Relative ages of rocks and events may also be determined using the law of crosscutting relationships, which states that geologic features such as igneous intrusions or faults are younger than the units they cut across.



Of the three basic rock types, igneous rocks are most suited for radiometric dating.However, sedimentary rocks can be age dated if a volcanic ash horizon or a diabase sill or dyke can be found within the sequence.For example, if you find a dinosaur bone in a sedimentary sequence and you find an ash layer 10 meter above the bone and another ash layer 20 meters below it, you can determine the age of the two ash layers.Absolute dating places events or rocks at a specific time.

If a geologist claims to be younger than his or her co-worker, that is a relative age.

Rates of radioactive decay are constant and measured in terms of half-life, the time it takes half of a parent isotope to decay into a stable daughter isotope.