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Which fossil is a good example of a index fossil?

Ammonite because it appears in only 1 layer (limited time) but in 3 columns (multiple areas) Fem because it appears in multiple layers (long period of time) and in 3 columns (multiple areas) Gastropod because it appears in multiple layers (long period of time) and in 3 columns (multiple areas) Trilobite because it only appears in one layer (limited time) and in one column (single area).

1 answer

The best example of an index fossil from your options is the Ammonite.

Index fossils are characterized by the following criteria:

  1. Limited Time Range: They must have existed for a relatively short geological time period so that the time frame in which they are found can be accurately assigned.

  2. Widespread Distribution: They should be found in multiple geographic locations (across different strata) so they can be used for correlation between rock layers.

The ammonite meets these criteria well, as it existed during a specific time period (mostly in the Mesozoic era) and is found in various locations around the world, making it useful for dating and correlating the age of the surrounding rock layers.

The other options (Fem, Gastropod, and Trilobite) do not fit the criteria for index fossils as well as the ammonite. Trilobites are often found in multiple layers over a longer time span, making them less suitable as index fossils compared to ammonites.