Paleontology is the study of ancient life forms and their evolution using fossils - the preserved and petrified remains of life forms within sedimentary rocks. These may include the complete fossilised body of the organism, the more durable parts of the organism, or moulds of the organism showing either its internal or external surface features. The fossil record may also include tracks, burrows or faeces. Fossils can be useful in characterizing rock strata - to determine their age and the environment in which they were deposited. This information can be useful in mining industries.