Fluorine and fossils They are now assisted by chemists who are able to fix dates through the analysis of pollen, radioactive carbon, and fluorine found in connection with fossils..


Here the text is talking about basic paleontology.

Could anyone teach me in a simple way how fluorine is connected with fossils findings?

(This is originally about English test (TOEFL), but the subject in question does not in my opinion belong to ELL)
I checked the literature, it has been reported that fluorine ions replace hydroxyl ions in osseous tissue (bone) so by making a measurement of the flourine content of bone it is possible to estimate the age of the bones.

One early paper on the subject is Cook, S. F.; Ezra-cohn, H. C. An Evaluation of the Fluorine Dating Method. Southwestern Journal of Anthropology 1959, 15 (3), 276–290. DOI: 10.1086/soutjanth.15.3.3628977.

One method would be to use neutron activation anaylsis on bones to measure the flourine-19, using the n,gamma reaction. This method does have a problem as sodium-23 can form flourine-20 by a n,alpha reaction. As a result a correction will have to be made for the sodium content of the bones.

This is discussed in Cheng, T. P.; Anderson, H. D.; Mills, D. S.; Spate, V. L.; Baskett, C. K.; Morris, J. S. Determination of the fluoride distribution in rabbit bone using instrumental neutron activation analysis. J. Radioanal. Nucl. Chem. 1997, 217 (2), 171–174. DOI: 10.1007/BF02034437.