Fossils are the subject of paleontology, which investigates how old they are, how they were shaped, and what role they had in the evolution of life on Earth. Specimens are usually considered fossils if they are older than 10,000 years. The oldest fossils are about 3.48 billion years old to 4.1 billion years old. Image by Cobalt is licensed under CC BY-NC-SA 2.0.