Fossils

A fossil is the preserved trace of a plant or animal that lived long ago. Fossils are the only way we know what life on Earth was like before humans existed. Almost everything we know about dinosaurs, ancient sea creatures and the first humans comes from fossils dug out of rocks. Every fossil is a tiny window into a vanished world, and palaeontologists (the scientists who study fossils) are still finding new and surprising ones every year.

  • Oldest known fossilsApprox. 3.5 billion yearsMicrobial mats called stromatolites
  • First animalsApprox. 600 million yearsSoft-bodied Ediacaran creatures
  • Dinosaur era230 to 66 million years agoRuled the world for 164 million years
  • Largest dinosaur fossilPatagotitanApprox. 37 m long, 69 tonnes
  • Famous fossil siteBurgess ShaleCanadian Rockies, 508 million years old
  • Famous fossilLucyApprox. 3.2 million-year-old human ancestor

How a fossil forms

Becoming a fossil requires a lot of luck. For a creature to turn into a fossil, several things usually have to happen:

  1. The dead body must be quickly buried in mud, sand or volcanic ash before it can rot or be eaten.
  2. More layers of sediment must build up on top, slowly turning the buried body to rock.
  3. Minerals in groundwater seep into the buried remains over millions of years, gradually replacing the original material with stone.
  4. The rock must survive earthquakes, melting and erosion for millions of years.
  5. Finally, the rock must be pushed back to the surface and someone has to find it.

Famous fossils and what they taught us

  • Tyrannosaurus rex Sue: the most complete T. rex skeleton ever found. Discovered in South Dakota in 1990.
  • Archaeopteryx: a 150-million-year-old creature that was half dinosaur, half bird. Proved that birds evolved from dinosaurs.
  • Lucy: a 3.2-million-year-old skeleton of an early human ancestor (Australopithecus) found in Ethiopia in 1974.
  • Tiktaalik: a 375-million-year-old fish with primitive limbs, halfway between fish and amphibians.
  • Burgess Shale fauna: a treasure trove of strange Cambrian sea creatures preserved with their soft bodies intact.
Fact Modern birds are technically dinosaurs. The same group of small feathered theropod dinosaurs that survived the great asteroid 66 million years ago evolved into the 11,000 bird species alive today. So the chicken pecking around in your back garden really is the closest living relative of Tyrannosaurus rex.

Pick a topic below to dig deeper.

What Are Fossils?The remains or traces of a living thing preserved in rock, often turned to stone over millions of years.
How Fossils FormWhen a creature is quickly buried by mud or sand, its bones can slowly be replaced by minerals over millions of years, leaving a stone copy.
DinosaursThe huge group of reptiles that ruled the land for over 150 million years until they died out 66 million years ago.
Trace FossilsFossils of what creatures did, not what they were. Footprints, burrows, and even poo can become trace fossils.
The Fossil RecordThe whole collection of fossils found around the world. Tells the story of how life on Earth has changed.
Famous Fossil SitesPlaces where fossils are unusually common. The Burgess Shale, La Brea Tar Pits, and Lyme Regis are world-famous.
Living FossilsCreatures alive today that look almost exactly like their fossil ancestors of hundreds of millions of years ago. The coelacanth and the horseshoe crab.