Fossils

• Fossils are the remains of organisms from many thousands of years ago, which can be found in rocks
• From gradual replacement

  • Things like teeth, shells and bones don’t decay so they last when they are buried
  • They are eventually replaced by minerals, forming a rock-like substance
• From casts and impressions

  • When an organism is buried in a soft material, the clay hardens around it
  • The organism decays leaving a cast of itself
• From preservation

  • In amber and tar pits, there is no oxygen or moisture so decay microbes cant survive
  • In glaciers it’s too cold for the decay microbes to work
  • Peat bogs are too acidic for decay microbes
• Some animals don’t fossilise due to:

  • Being soft bodied so it decays completely
  • They may have been destroyed due to geological activity