Final answer:
Fossils in layers of rock are estimated to be older, and younger based on the concept of relative dating, where fossils in deeper rock layers are older than those above them.
Step-by-step explanation:
Understanding Fossil Age through Rock Layers
Fossils found in layers of rock are used to determine their relative age in the study of paleontology. The principle of relative dating is applied here, which is based on the assumption that lower rock layers are older because they were deposited first. Consequently, fossils found in these lower layers are considered to be older than those found in the upper layers. To directly answer the question, fossils in layers of rock are generally estimated to be a) older, or younger in relation to their depth, with fossils in deeper layers being older than those in more superficial ones. The rock layers serve as a history book, offering a timeline where the deeper you go, the further back in time you are looking.
Moreover, fossil record refers to the ordering of fossils within these rock layers, which provides vital evidence for the history of life on Earth. The age of fossils can also be measured more precisely through radiometric dating, using the decay rates of radioactive materials to determine the age in years, which goes beyond relative dating techniques.