Why should the percentage of lead to uranium in zircon crystals (the key to ordinary uranium-lead, radiometric dating) depend on which geologic period they are found in?

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Any kind of object clearly restricted to a specific point in the geologic column would do just fine.

If green dice were found only in the middle Ordovician strata, they would make excellent "index fossils." Evolution should be seen as an explanation of the faunal succession, a succession which was worked out long before evolution dominated the scene.

(Far from being a rubber stamp, radiometric dating would go on to revolutionize our understanding of the Precambrian.) Thus, it became possible to date strata directly from index fossils.

Note that evolution has nothing to do with how the index fossils are used to date strata!

By then, the relative ages (order) of the geologic column had already been worked out in some detail.

Radiometric dating would later confirm the relative ages of the strata and tie them to absolute dates.

It's just one of the tricks that have been used to make the work a little more precise. I believe he has confused the use of index fossils with evolution.

One creationist editor, who is more mellow than his unfortunate statement suggests, phrased the argument thus: Unfortunately the geologists date the rocks as the paleontologists tell them to. That passage might have come out of one of Henry Morris' books, except that Morris usually avoids crude slander. Hovind is not aware of the fact that by 1815 the broad outlines of the geologic column from Paleozoic times onward had been worked out by people who were mostly geologists.

Evolution, working in tandem with geologic ages, can explain why we have index fossils, but evolution is needed to make the index fossils useful for dating strata.