The scientific method used to estimate the age of rocks and fossils is known as radiometric dating. This technique measures the decay of radioactive isotopes present in the material. By analyzing the ratio of parent isotopes to daughter products, scientists can calculate the time elapsed since the rock or fossil formed. Different isotopes are used for dating different age ranges, such as carbon-14 for recent fossils and uranium-lead for ancient rocks. This method is crucial for understanding geological and evolutionary timelines.