Paleontology

Paleontology is the science that studies life forms that existed on Earth in ancient times. The science is based on fossils—the remains or traces of ancient organisms preserved in rock, such as bones, teeth, shells, petrified wood, and footprints.

The science combines two fields: biology (the study of living things) and geology (the study of rocks and the Earth). Researchers use layers of rock to determine the sequence of time, and they compare the structure of organisms alive today with ancient life to understand how ancient organisms lived.

How fossils form

Fossils typically form when an organism dies and is buried in sediment, ash, or mud on the ocean floor before it decomposes. Over a long period, minerals in the water replace the original material, turning it into rock while preserving the original structure. For this reason, organisms with hard shells or bones are far more common as fossils than soft-bodied organisms.

Branches

The science divides into branches. One focuses on vertebrate animals, another on invertebrates. There is a branch specialized in ancient plants, and one that studies very small organisms requiring a microscope, such as pollen. Another branch works with traces such as footprints and burrows to determine the behavior and habitat of ancient organisms.

Time and age determination

The age of fossils is determined by two complementary methods. Stratigraphic dating relies on the principle that lower rock layers are older than upper ones. The other method uses the decay of radioactive elements in rocks, which provides a numerical count in years. The results of both methods are combined to build a geological timescale.

Significance

Paleontological data provides the foundation for understanding the evolution of life and shows periods of mass extinction when large numbers of organisms disappeared. Knowledge of fossil layers is also used to search for natural resources beneath the Earth's surface and to study climate change in ancient times.