Radioactive dating is used to determine the age of fossils.
Radioactive isotopes are commonly used for dating .
Radioactive isotopes are commonly used to determine fossil age.
Radioactive isotopes are commonly used to do what to the age of fossils?
  - duplicate itself
  - observe it
  - debate them
  - Temperature
  - Time and energy
  - determine them
  - remove them
  - assign them