Evidence for Evolution: Fossils

• How do fossils provide evidence for evolution?

  They are remains of ancient organisms
• What are fossils?

  Remains of organisms from millions of years ago
• Where are fossils typically found?

  In rocks
• How can fossils form when parts of organisms have not decayed?

  Conditions needed for decay are absent
• What conditions can prevent decay?

  Cold temperatures, lack of oxygen, lack of water
• How can fossils form if an organism decays?

  Parts are replaced by minerals during decay
• What are preserved traces of organisms?

  Footprints or spaces left by roots
• Why are there very few fossils of early life-forms?

  Soft-bodied organisms rarely form fossils
• What has happened to many fossils of early life-forms?

  They have been destroyed by rock changes
• What does the lack of early life-form fossils mean for scientists?

  They cannot be certain how life began
• What does extinction mean?

  No remaining individuals of a species alive
• What can cause a species to become extinct?

  Catastrophic events, environmental changes, competition
• What catastrophic event led to the extinction of dinosaurs?

  An asteroid colliding with the Earth
• How can environmental changes lead to extinction?

  Changing weather, new diseases, new predators
• How can competition lead to extinction?

  New species compete for scarce resources
• What are the three ways fossils can form?

  1. Parts of organisms do not decay
  2. Organism decays but parts are replaced by minerals
  3. Preserved traces like footprints or root spaces
• What are the reasons for species extinction?

  • Catastrophic events (e.g., asteroid impact)
  • Environmental changes (e.g., weather, diseases)
  • Competition from more successful species