1) That the rate of decay happens to be constant throughout time. 2). That the isotope abundances into the specimen dated haven’t been changed during its history by addition or elimination of either moms and dad or child isotopes 3) that after the stone first formed it included an understood amount of child material («Radioisotopes while the chronilogical age of the planet earth» pg v)

We should observe that past processes may never be occurring at all today, and therefore some might have taken place at rates and intensities far not the same as comparable procedures today. ( «Radioisotopes while the chronilogical age of the planet earth» pg vii)