Fossils and extinction

• What are fossils?


  Things left behind by dead organisms
• What are the 3 ways fossils are formed?

  • Gradual replacement by minerals
  • Casts and impressions
  • Preservation
• Properties of gradual replacement by minerals?

  • Decay really slowly
  • Rock like substances
• What are casts?


  Organisms that are buried in soft material
• What are impressions?


  Marks on the ground such as footprints that are on the ground for a long period of time
• What is preservation?

  • There is no decay at all
  • Happens when organisms get stuck in amber or tar pits
• Why are fossils used to as evidence for evolution?


  They show us how species have changed over millions of years
• What does it mean for a species to become extinct?

  There are no remaining individuals of a species still alive
• Suggest 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