Absolute age dating
The fossil record may be incomplete and may never fully completed, but there are still many clues to evolution and how it happens within the fossil record.
One way that helps scientists place fossils into the correct era on the Geologic Time Scale is by using radiometric dating.
Different isotopes have different half-lives and sometimes more than one present isotope can be used to get an even more specific age of a fossil.
It implies that relative dating cannot say conclusively about the true age of an artifact.
Let's say you found a fossil you think to be a human skeleton.
The best radioactive element to use to date human fossils is Carbon-14.
However, archeologists still require further information to find out the items that are oldest and those that are youngest in the order.
It is left for absolute dating to come up with the precise age of an artifact.