Fossils are the remains or traces of ancient life that have been preserved by natural processes, from spectacular skeletons to tiny sea shells. Imprints, tracks and trails can also become fossilised, like dinosaur footprints or worm burrows. These are called trace fossils. By studying the remains of life and the traces it left behind we can learn a lot about how animals and plants lived and behaved millions of years ago.

Ichthyosaur skull early Jurassic

How do fossils form?

The way a fossil forms depends on a few things. The most important step is that the remains or traces of life must be buried, the quicker the better. The longer they remain exposed the more likely it is that they will be destroyed by scavengers or by the environment itself.

Imagine a desert versus the bottom of a deep sea… wind blasted sand dunes and hungry scavengers versus still, murky waters where gloopy mud is laid down steadily… where do you think fossils are more likely to form?

Apart from burial the other key points are…

  • Hard parts best. Got hard parts? Bones or shells? Then you are more likely to become a fossil because soft bits rot away quickly.
  • Where do you live? If there is sediment like mud or sand being laid down then you have a chance to be buried by it and fossilised.
  • The recipe for success. Once buried there is a chance minerals can start to fill gaps in your remains or even replace them, basically turning them into stone. This is when fossilisation really happens and depends a great deal on what natural minerals are in the sediment.
  • And finally… with luck the rock layer you are preserved in will be eroded and your fossilised remains
  • exposed, ready for the chance to be discovered.
Iguanodon dinosaur bone, lower cretaceous period, 142 million years old

Here you can see a short animation of how a fossil is made (credit: