Sonnike,
quote:
Using index fossils to date the rock layers, and then using the rock layers to date the fossils they contain
Nope. Rocks of certain ages have been found to contain fossils so reliably in rocks of said age, that they can be considered indicators of the age of the rock without independent dating of the rocks.
The dates of the rocks that contain the fossils are derived independently of the fossils to begin with. It is not circular.
If independently dated Cretaceous rocks contained only nuts, & Jurassic only bolts, & there were found to be no exceptions, then it can be reliably inferred that rocks containing bolts are of Jurassic age, & those containing nuts are of Cretaceous age.
quote:
You guys are good at this type of logic:
Glad you see it that way. The above is a perfectly logical inference. Perhaps you would like to point out the illogic, without forcing me to repeat myself? To be a circular argument, you have to accept the conclusion in order to accept the premises. It goes like this:
Premises:
1/ In any given column, certain fossils are only found in certain strata.
2/ This is true of the same fossils around the world.
3/ The rocks are independently dated & agree that said fossils are of the same age range, wherever they were tested.
Inference:
The fossils in question can be considered tied to the age range given by the independent dating.
Conclusion:
Index fossils are reliable indicators of the potential age range of the rock.
I can't see any circular reasoning, can you?
Mark
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Occam's razor is not for shaving with.
™ Version 4.2
