Potassium argon dating is useful for determining the age of of match dating
The method relies on satisfying some important assumptions: Given careful work in the field and in the lab, these assumptions can be met.
The rock sample to be dated must be chosen very carefully.
The fossil is given an age limit between the dated volcanic layers.
The first Hominid fossil dated using this method was an Australopithecus boisei (initially called Zinjanthropus boisei) specimen discovered by Mary Leakey in the Olduvai Gorge in 1959.
Volcanic ash layers are relatively common along the Great Rift Valley of east Africa.
This is not a significant problem for igneous rocks, but it affects the usefulness of the techniques for other forms of rock that have more complex heating histories.
For these other rocks argon-argon (40Ar - 39Ar) dating can be more useful.