Radioactive isotopes used in absolute dating
The infilling material is magma, which then solidifies into rock.
Magnetic minerals in the magma are aligned with the magnetic poles, much like the needle of a compass. Sedimentary rock is composed of the weathered remains of a variety of rocks of all ages.
Isotopic dating relies on the amount and rate of decay of the isotope present in rock.
Fossils are generally not dated directly by isotopic dating, however.
You can't date all minerals using the radiometric dating method because not all minerals have radioactive isotopes.
This technique is primarily used to date igneous rocks.
Certain fossils only appear in rocks from a certain geologic age.
This method is known as 'relative dating' and the age is called the 'relative age'.
Starting when the melt solidifies these unstable parent isotopes begin to decay into their daughter isotopes.
Radiometric/Isotopic dating uses the ratio of parent to daughter isotopes to determine when the rock formed.