Fossils & Extinction

• Fossils are the remains of organisms from millions of years ago, which are found in rocks.
• Why are fossils used to as evidence for evolution?


  Fossils show us how species have changed over millions of years
• Why is the fossil record incomplete?

  • Some fossils formed long ago may have been destroyed since
  • Some organisms are soft-bodied so do not fossilise well
• Three main ways fossils can form

  1. Hard body parts, such as bones and shells, which decay very slowly, are gradually replaced by minerals, forming rock-like substances.
  2. Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock.
  3. Some parts of organisms may not decay at all. For example, dead animals and plants can be preserved in amber, peat bogs, tar pits, or in ice.
• Why might a dead animal be preserved in a tar pit, rather than decay?

  Not enough oxygen for decay to take place

  The lack of oxygen means that microorganisms can't respire aerobically and so can't carry out the decay process.
• What does it mean for a species to become extinct? 

  There are no remaining individuals of a species still alive.
• Suggest three ways a species may become extinct.

  • Rapid environment change such as an increase in temperature
  • Reduction in habitat as it could reduce food and living space
  • Increase hunting as individuals are directly killed 
  • The spread of a new disease 
  • Introduction of a new competitor or predator 
  • A catastrophic event, such as an asteroid strike