Question

Which phrase describes organisms that formed index fossils?

Answer 1

Answer:

A.) Are extinct

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Answer 2

Options (1), (2), and (4)

Index fossils are usually defined as those fossils that were present on earth for a very short period of time. They were very broadly distributed in almost all parts of the world. They were comparatively smaller in size and comprised of hard parts that were preserved under favorable conditions which are found at many places in the present. These are extinct species. For example, trilobites and ammonites.
These index fossils are very useful because it helps in determining the age of the fossils as well as rocks by applying the radioactive dating method.
thus, the correct answers are options (1), (2), and (4).