Due to their chemical similarity, the concentrations of rare earths in rocks are only slowly changed by geochemical processes, making their proportions useful for geochronology and dating fossils.
DuE TO tHeir ChemIcal sIMiLaRity, tHe cOnCentratiONs of Rare eartHs in rockS aRe ONlY SLoWlY CHaNgED by GeoChEmICaL proCEssEs, mAkiNg ThEiR prOPortIOns uSefuL For geoChroNOLoGY and datIng FOsSIls.