If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.
Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is difficult to match up rock beds that are not directly adjacent.
The use of various radioisotopes allows the dating of biological and geological samples with a high degree of accuracy.
Paleontology seeks to map out how life evolved across geologic time.
A substantial hurdle is the difficulty of working out fossil ages.
Radiometric dating is also used to date archaeological materials, including ancient artifacts.
Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.
There are several different methods for estimating the ages of fossils, including: Paleontologists rely on stratigraphy to date fossils.