Final answer:
Potassium-40 and uranium-235, not carbon-14, are used for determining the age of dinosaur bones because C-14's half-life is too short for the ancient age of dinosaurs.
Step-by-step explanation:
The isotope commonly used for determining the age of dinosaur bones is not carbon-14 (C-14), because its half-life is too short to measure the age of dinosaur fossils, which are over 65 million years old. Instead, isotopes with longer half-lives such as potassium-40 (40K) or uranium-235 (235U) are used for such ancient specimens.
Radiometric dating measures the ratio of parent to daughter atoms in a sample to determine how many half-lives, or what fraction of a half-life, has passed since the organism died. By knowing these ratios and the decay rate of the isotope, geologists can calculate the old age of these fossils.