Paleontology and Fossils

Paleontology is the scientific study of life that existed before the start of recorded history, based on the fossil record. A fossil is the preserved remains, impression, or trace of a once-living organism. Most fossils form when an organism is buried in sediment soon after death and its hard parts — shells, bones, teeth, or woody tissue — are gradually replaced or infilled by minerals over long periods. Soft tissues rarely survive, so the record is biased toward organisms with durable skeletons.

Fossils are commonly divided into body fossils and trace fossils. Body fossils preserve part of the organism itself, while trace fossils, or ichnofossils, record activity such as burrows, tracks, and footprints. Among invertebrates, ammonites and trilobites are widely studied because they are abundant, distinctive, and changed quickly through time, making them useful for dating rock layers. Crinoids, brachiopods, and corals are other common marine fossils. Insects such as beetles (Coleoptera) and flies (Diptera) are sometimes preserved in amber, hardened tree resin that can trap small organisms in fine detail.

Because layered sedimentary rocks form in sequence, fossils help geologists correlate strata and reconstruct ancient environments. Fossils of plants, marine animals, and land vertebrates indicate past climates, sea levels, and the positions of continents. Paleomaps, which show how landmasses were arranged in earlier geological periods, draw on this evidence together with the study of plate movement.

Frequently asked questions

What is the difference between a body fossil and a trace fossil?

A body fossil preserves part of the organism, such as a bone or shell. A trace fossil records behavior, such as a footprint, burrow, or track.

Why are trilobites and ammonites useful to geologists?

They were widespread, evolved rapidly, and have recognizable forms, so particular species occur in narrow time ranges and help date the rock layers that contain them.

How are insects preserved in amber?

Sticky tree resin can trap small organisms, then harden and fossilize over millions of years, sometimes preserving fine anatomical detail.