Final answer:
An index fossil must be easily recognizable, abundant and widely distributed, and have existed for a short geologic time to be effective in dating rock layers.
Step-by-step explanation:
Features Necessary for an Index Fossil
The three main features necessary for an index fossil are:
- Easily Recognizable: An index fossil must be easily identifiable and distinguishable from other fossils, which aids in quick recognition and classification of the geologic period.
- Abundant and Widely Distributed: To be useful as an index, the organism from which the fossil is derived must have been widespread geographically and occur in sufficient numbers to ensure a good chance of being found by paleontologists.
- Lived for a Short Period: For a fossil to serve as a good index, it is crucial that the organism lived for a relatively short geologic timeframe. This allows for more precise dating of the rock layers in which it is found.
For instance, the Belemnites are an example of an index fossil from the Mesozoic era, which provides information about the age of the rocks in which they are found due to their distinctive features and temporal distribution.