A common method for determining the age of fossils is radiometric dating, which measures the decay of radioactive isotopes in rocks and organic materials. By analyzing the ratio of parent to daughter isotopes, scientists can estimate the time since the organism's death, providing an age for the fossil. Carbon-14 dating is often used for relatively recent fossils, while other isotopes, like uranium-238, can date much older specimens. This technique is crucial for understanding the timeline of life on Earth and the evolution of species.