Metamorphic rocks may also be radiometrically dated.However, radiometric dating generally yields the age of metamorphism, not the age of the original rock.
Simply stated, each bed in a sequence of sedimentary rocks (or layered volcanic rocks) is younger than the bed below it and older than the bed above it.
This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.
becoming known as “the Father of English Geology.” Using Steno’s principles, a relative time scale was developed in the nineteenth century with names derived from areas studied and characteristics of the rocks in those areas.
The figure in section 7.1 shows the names applied to units and subunits of the Geologic Time Scale.
The nuclear decay of radioactive isotopes is a process that behaves in a clock-like fashion and is thus a useful tool for determining the absolute age of rocks.