Ancient fossils are the preserved remains or traces of organisms that lived millions of years ago. They can include bones, teeth, shells, and even imprints of plants or 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, often involving mineral replacement or the preservation of organic material. Notable fossil sites, like the La Brea Tar Pits or Dinosaur National Monument, have yielded significant discoveries that enhance our knowledge of ancient life.