Fossilisation is a rare process, the vast majority of deceased organisms disappear without leaving a trace

In order for fossilisation to occur, the following conditions are required:

  • Hard body parts (bones, teeth, shells) – soft body parts will not fossilise, but may leave behind trace evidence (e.g. imprints)
  • Preservation of remains (protection against scavenging, erosion and environmental damage)
  • High pressure to promote mineralisation of remains (i.e. turn hard body parts into fossilised rocks)
  • Anoxic (low oxygen) conditions to protect against oxygen damage and prevent decomposition by saprotrophs

The stages of fossilisation generally occur as follows:

1.  Death and decay – Soft body parts are decomposed or scavenged, leaving only the hard body remains

2.  Deposition – The hard remains are rapidly covered with silt and sand, and over time more layers continue to build

3.  Permineralisation – Pressure from the covering layers of dirt/rock cause the hard organic material to be replaced by minerals

4.  Erosion / exposure – Movement of earth plates may displace the fossil and return it to the surface for discovery

Process of Fossilisation