Fossil dating relative
These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils.
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.
Such a preserved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 years.
The observation that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century.
One known example where this assumption was used is very misleading.
Ice cores showed the age of a military plane buried in the artic as thousands of years old.
The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.