In order for a species of an organism to be used as an index fossil, it must have been geographically widespread and must have:

The organism to be used as the index fossil must have been geographically widespread and have lived for a geologically short time.

Index fossils refers to those fossils used by geologists to determine the relative age of rock strata or other fossils with ease.

An index fossils need to have some characteristics in order to be used and includes:

In conclusion, the organism to be used as the index fossil must have been geographically widespread and have lived for a geologically short time.

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Lived for a geologically short time.

Explanation:

Index fossils are a type of fossils that are used by geologists so that they can determine the relative age of rock strata or other fossils with ease. These fossils need to have several characteristics in order to be used as such. Some of those characteristics are:

Being widespread means that they can be used in a big portion of the world. Existing for a relatively short period means that they give a very good indication about the age of the rock strata and other fossils that are found. By being clearly distinct from other fossilized species no time and effort are lost for them to be determined as the required species, so all of the focus goes on everything around them.