Absolute vs relative age dating
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.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.Gaps in the geologic record, called unconformities, are common where deposition stopped and erosion removed the previously deposited material.
This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.
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.
Faunal Succession: Similar to the law of superposition is the law of faunal succession, which states that groups of fossil animals and plants occur throughout the geologic record in a distinct and identifiable order.
Following this law, sedimentary rocks can be “dated” by their characteristic fossil content.