A fossil is the preserved remains or traces of ancient living organisms, typically found in sedimentary rock. Fossils can include bones, shells, imprints, or even traces like footprints. They provide valuable information about the history of life on Earth and how species have evolved over millions of years. Fossils are formed through a process called fossilization, which usually occurs when an organism is buried quickly after death, protecting it from decay. Over time, minerals in the surrounding sediment replace the organic material, creating a rock-like structure. This process helps scientists study extinct species and understand past environments, contributing to fields like paleontology and geology.