The correct answer is C. Radioactive dating
Step-by-step explanation
Radiometric dating also called radioactive dating is a scientific method to know the age of rocks and old data objects. This method is based on the number of radioactive atoms (unstable by nature) that, over time, disintegrate into stable atoms. Therefore, to know the age of a rock, scientists compare the amount of unstable radioactive atoms with the number of stable atoms to know their age. This method has been one of the most effective ones to know the age of Earth as though this scientist can determine the age of the oldest fossils or rocks and based on this they can know how long has Earth existed. So, the correct answer is C. Radioactive dating