Which of the following is NOT a feature of index fossils?

Index fossils are essential tools in the field of geologic mapping and relative dating because they provide insight into the age of rock layers and help establish the relative timelines of various geological formations. For a fossil to be considered an index fossil, it must possess specific characteristics that facilitate its use in these processes.

One significant feature of index fossils is that they are widely distributed across different geographical areas. This widespread occurrence means that when geologists find an index fossil in one location, they can infer that the corresponding rock layer in another location, even far away, may also date to the same period. This aspect is crucial for correlating rock layers across vast distances.

Another important trait is that index fossils existed for a relatively short geologic timeframe, which allows for more precise dating of rock layers. If a fossil species thrived for only a limited time, finding that fossil in a rock layer indicates that the rock must be from that specific time period.

Furthermore, index fossils play a vital role in assisting geologists with dating rock layers effectively. By identifying and utilizing index fossils, geologists can establish a timeline for sedimentary layers, contributing to our understanding of the Earth's history.

The characteristic that is not aligned with index fossils is their uniqueness to a single formation. Instead,