Asked by Jessica

Why Devonian could not be considered an index fossils?

How can the occurrence of fossils and their known age ranges be used to date rocks?

Need help by understanding the question.
Answered by Ms. Sue
What does your text say about dating rocks, index fossils, and the Devonian period?
Answered by Jessica
Fossil Occurrence and the Age of Rocks:

Groups of fossil organisms occur throughout the geologic record for specific
intervals of time. This time interval is called the fossil’s range. Knowing the
range of the fossils of specific organisms or groups of organisms can be used
to relatively date rocks and sequences of rocks. In this laboratory exercise,
you will use such information to assign a date to a hypothetical unit of rock.
Answered by Jessica
The text above^^ is for this question: How can the occurrence of fossils and their known age ranges be used to date rocks?
Answered by Ms. Sue
Fossils died at the same time the rocks were formed.
Answered by Jessica
I still don't understand.
Answered by Jessica
how? why?
Answered by Ms. Sue
Please read about the three different kinds of rocks.

http://www.kidsloverocks.com/html/types_of_rocks.html

Answered by Jessica
okay, and how about this question. Why Devonian could not be considered an index fossils?
Answered by Ms. Sue
I'm sorry, but I don't know. Perhaps if you read this site carefully, you'll find the answer.

http://www.britannica.com/science/Devonian-Period
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