Answer:
The answer is Option C: Index fossils.
Explanation:
Index fossils are used to identify geologic periods or faunal stages in rock layers. These fossils must have a wide geographic distribution and manifest obvious evolutionary trends to help geologists and others who need this geological data to better understand the time scale and to pinpoint a time period. For example, ammonites were common during the Mesozoic Era, but they were extinct by the Cretaceous period. Â Geologists would use ammonites to help determine this time frame if present.
