If a radioactive isotope (the parent element) was originally present in a rock at the time of its formation, then that isotope would give rise, by radioactive decay, to decay products (daughter elements).
(a radioactive isotope; was; originally present in a rock at the time of its formation) (isotope; would give; rise; to decay products; T:then)
a radioactive isotope isotope
was would give
originally present in a rock at the time of its formation
rise to decay products T:then