History of life on Earth: Fossils and fossil formation

Fossil

The preserved remains or traces of an organism that lived a long time ago, usually found in rock.

Palaeontologist

A scientist who studies fossils to uncover the history of the Earth.

Palaeoanthropologist

A palaeontologist who specialises in studying human ancestors.

Petrification

The process in which the remains of organisms are replaced by minerals such as silica or calcium and turned into stone.

Sedimentary rock

Rock formed from layers of materials such as mud, sand, salt, pebbles or carbonate.

Transitional fossil

A fossil showing characteristics of two different groups, representing an intermediate stage between them.

Fossil formation – sediment

Shortly after an organism dies, it is buried by sediment such as volcanic ash or silt, protecting its remains from rotting.

Fossil formation – layers

More layers of sediment accumulate above the remains. Minerals such as silica slowly replace calcium phosphate in the bones.

Fossil formation – movement

Movement of tectonic plates lifts sediments and pushes fossils closer to the Earth's surface.

Fossil formation – erosion

Rain, rivers and wind wear away rock layers, eventually exposing the preserved fossils.

Examples of fossils

Bones, shells, footprints, hardened faeces, petrified tree trunks and imprints of leaves or small animals.

Fossils preserved in ice

Woolly mammoth remains are an example of fossils preserved in ice.

Fossils preserved in tar

Sabre-toothed cat bones have been found preserved in tar pits.