Paleontology, or palaeontology, is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised faeces (coprolites), palynomorphs and chemical residues.
Biostratigraphy uses those fossils, tracks, and other finds in an effort to figure out how old a certain layer of rock and sediment is.
Once a petroleum geologists knows how old a particular area is, they know the potential for finding natural resources such as oil or natural gas.