Misleading results can occur if the index fossils are incorrectly dated.
Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution.
This is difficult for some time periods, however, because of the barriers involved in matching rocks of the same age across continents.
Paleontology seeks to map out how life evolved across geologic time.
A substantial hurdle is the difficulty of working out fossil ages.
The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff.
The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata. Such index fossils must be distinctive, globally distributed, and occupy a short time range to be useful.
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