Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Relative dating determines which of two fossils is older or younger than the other but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower rock layers were laid down earlier, so they are assumed to contain older fossils. This is illustrated in Figure below . Answer: relative
What type of dating determines which of two fossils is older or younger than the other but not their age in years?