Need asap will mark sully works as a geologist in the southwestern united states. he plans to choose an unstable isotope to find the absolute age of a rock sample. which two aspects must he consider before making his choice? (more than 1) 1. there should be a sufficient amount of the selected isotope in the rock. 2. the isotope should be one that decays at a very fast rate. 3. the isotope must not be found in any neighboring rocks. 4. the half-life of the isotope must be long enough to capture the age of the rock. 5. there should be more than one unstable isotope in the rock.