sentences: the radioactive isotope content of a rock means the amount of elemental isotopes of the parent isotopes & calculating the age of rocks requires investigating the original amount of the elemental isotopes of the parent isotopes ->  calculating the age of rocks requires investigating the radioactive isotope content of that rock  calculating the age of rocks requires investigating the radioactive isotope content of that rock & radiometric dating is a kind of method to determine the absolute age of the rock ->  radiometric dating requires the radioactive isotope content of a rock  radiometric dating requires the radioactive isotope content of a rock & radiometric dating is used to identify / determine the absolute age of the rock ->  the radioactive isotope content of a rock can be used to identify the absolute age of the rock  the radioactive isotope content of a rock can be used to identify the absolute age of the rock & the absolute age of a rock is the amount of time passed since a rock was formed -> the radioactive isotope content of a rock can be used to identify the amount of time passed since a rock was formed