GEOSCI GEOSCI

GEOSCI / PALAEONTOLOGY

How a fossil forms

Two animals, two very different worlds, one process. Pick a creature to follow. At any stage you can switch to the other one with the tab on the right edge, and you will stay at the same point in the story. Their stories meet at the very end.

Then scroll down ↓

01 / 07 · Alive

Alive

02 / 07 · Death

Death

03 / 07 · Burial

Burial

04 / 07 · Minerals

Minerals move in

05 / 07 · Rock

Turning to rock

06 / 07 · Erosion

Back to the surface

07 / 07 · Discovery

Discovery

The whole journey

Why fossils are so rare

Every fossil survived a chain of lucky breaks. Break any link and the animal is gone without a trace, which is why the fossil record is only a tiny, patchy sample of the life that once existed.

  1. AliveNeeds hard parts that can last.
  2. DeathScavengers and decay strip the soft tissue.
  3. BurialQuick burial protects the remains.
  4. MineralsGroundwater fills or replaces the original material.
  5. RockCompaction and cementation lock it in.
  6. ErosionUplift and weathering expose it again.
  7. DiscoverySomeone has to find it before it crumbles.

A few dozen

One study estimated that around 2.5 billion adult T. rex lived over the species' history, yet only a few dozen reasonably complete skeletons have been found. Over 99% of all species that ever lived are extinct, and most left no fossil at all.

Words worth knowing

Taphonomy
The study of what happens to an organism between death and discovery.
Permineralisation
Minerals from groundwater fill the pores and cavities of bone or shell.
Replacement
The original material dissolves and a mineral takes its place, grain by grain.
Lithification
Loose sediment turning into solid rock by compaction and cementation.