Final answer:
An effective index fossil must be widespread geographically, short-lived in geological time, and abundant in the fossil record, hence the answer is 'All of the above'.
Step-by-step explanation:
An effective index fossil must have several key characteristics that make it particularly useful for dating geological layers. These characteristics are:
- Widespread geographically - Index fossils must have a distribution that spans different regions, which allows them to be used in correlating age across broad areas.
- Short-lived in geological time - They should have existed for only a relatively brief period in geological terms so that they can pinpoint a specific time.
- Abundant in fossil record - There should be a large number of specimens in the fossil record to ensure they can be found and identified with ease.
Therefore, the answer to what makes an effective index fossil is indeed D) All of the above.