Ancient fossils are the preserved remains or traces of organisms that lived millions of years ago. They can include bones, teeth, shells, and even footprints. Fossils provide valuable information about the Earth's history and the evolution of life, helping scientists understand how species have changed over time. Fossils are typically found in sedimentary rocks, where layers of mud and sand have compacted over time. The process of fossilization can take thousands to millions of years, and it often requires specific conditions, such as rapid burial and low oxygen levels. Notable examples of ancient fossils include those of dinosaurs and early marine life.