Which of the following statements is false? a. scientists can date any radioactive material back only three half-lives; after this there's not enough parent material left to measure. b. carbon-14 dating is used to date material that was once alive and has not been petrified. c. isotopic dating can be used only in a closed system, where neither parent nor daughter material has escaped. d. isotopic dating of igneous rocks tells you when the magma or lava cooled to a solid. e. the "radiometric clock" starts when a radioactive mineral cools below its closure temperature.