Editing Fossil (section)

=== Index ===
{{Main|Index fossil}}

Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify [[geologic column|geologic periods]] (or faunal stages). They work on the premise that, although different [[sediment]]s may look different depending on the conditions under which they were deposited, they may include the remains of the same [[species]] of fossil. The shorter the species' time range, the more precisely different sediments can be correlated, and so rapidly evolving species' fossils are particularly useful as index fossils. The best index fossils are common, easy to identify at species level and have a broad distribution—otherwise the likelihood of finding and recognizing one in the two sediments is poor.