Question

Which of the following are reasons why index fossils are chosen for determining age of rocks? Select all that apply.
Responses

Are always dinosaurs
Are always dinosaurs

Limited life existence in geologic time
Limited life existence in geologic time

Found commonly in rocks
Found commonly in rocks

Distributed over a very wide range

Answer 1

The reasons why index fossils are chosen for determining the age of rocks include:

- **Limited life existence in geologic time**: Index fossils are from organisms that had a short, well-defined time period in which they existed, which helps narrow down the age of the rock layers.

- **Found commonly in rocks**: Index fossils are typically found in many different locations, which makes them useful for correlating the age of rock layers across different geographic areas.

- **Distributed over a very wide range**: This allows for better identification and correlation of the fossils, as the same index fossil can be found in different places, indicating that the rocks from different locations were formed during the same time period.

The statement "Are always dinosaurs" is not a reason for choosing index fossils, as index fossils can come from a variety of organisms, not just dinosaurs.

So, the correct responses are:

- Limited life existence in geologic time
- Found commonly in rocks
- Distributed over a very wide range