First I'd like to draw attention here to
Post 39418, which gives more information about radiometric dating. The problem is that since you started this thread with a post that already existed in another thread, we have parallel discussions happening.
I see two assumptions that cannot be verified: both specimens exposed to same amount of bacteria & same exposure to groundwater.
If you had looked at the site I linked to, it says:
Fluorine analysis can be used only as a relative dating method because the rate of decay and the amount of dissolved minerals in the ground water varies from site to site. In other words, the biochemical clock that this method relies on runs at a different rate in different environments. Fluorine analysis is primarily used for verifying whether or not two fossils in the same strata at a site were in fact contemporaneous. If not, then at least one of them must be physically out of context.
The original question was:
a fossil, that dates a few thousand year old, is buried in a geological layer that dates a millions years old.
If a fossil appears not to be
in situ, then fluorine dating can help determine that. Archaeologists can also look at other fossils existing in the same stratum of rock, which could possibly extend for miles. Taking samples from different parts of that stratum can help determine whether some of those fossils have younger ages. And as I said, we know the evolutionary history of some fossils so well (such as
foraminifera) that they can be used as index fossils to help date other fossils found with them.
Actually I'm not quite sure what your specific question is here . . . ?
