Question

fossils from perisphinctes are used as index fossils, which means that they are characteristic of a specific span of geologic time or environment. when perisphinctes fossils are found in a rock layer, they can be used to estimate that rock layers age relative to other layers. these fossils also help scientists to correlate the age of rock layers across different locations. as an index fossil, perisphinctes fossils likely have which of the following characteristics? choose 1 answer: a perisphinctes fossils occur over a long geologic period. b perisphinctes fossils lack unique, recognizable physical features. c perisphinctes fossils have a broad geographic distribution.

Explanation:

To determine the correct answer, we analyze the characteristics of index fossils. Index fossils are used to correlate rock layers across different locations and estimate the age of rock layers.

• Option A: Index fossils typically exist for a relatively short geologic time span (not long) to be useful for precise dating, so A is incorrect.
• Option B: Index fossils need to have unique, recognizable physical features to be identified easily, so B is incorrect.
• Option C: For an index fossil to help correlate rock layers across different locations, it must have a broad geographic distribution, which matches the role of Perisphinctes fossils as described (helping correlate ages across different locations).

Answer:

C. Perisphinctes fossils have a broad geographic distribution.