So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
In the past, relative dating methods often were the only ones available to paleoanthropologists.
As a result, it was difficult to chronologically compare fossils from different parts of the world.
These processes result in All of these processes confuse the stratigraphic record.
In many cases, however, it is possible to reconstruct the original sequence of strata so that they can be used for relative dating.
index fossils are those fossils which have wide geographical distribution and short life span.