Fossils

• Why are there very few fossils for early life-forms?

  Soft-bodied organisms rarely form fossils
• What is a fossil?

  Remains of organisms from millions of years ago
• 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 of the organism are replaced by minerals
• What are preserved traces of organisms?

  Footprints or spaces left by roots
• Why do soft-bodied organisms rarely form fossils?

  They lack shells or skeletons
• What is the impact of changes to rocks in the Earth's crust on fossils?

  Many fossils have been destroyed
• What does the lack of early life-form fossils imply?

  Scientists cannot be certain how life began
• What defines a species as extinct?

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

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

  An asteroid colliding with the Earth
• How can changing weather patterns affect species survival?

  They can lead to extinction of species
• How can a new disease lead to extinction?

  It can kill all individuals of a species
• How can competition with a more successful species lead to extinction?

  It competes for scarce food or water
• 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 patterns)
  • Competition with more successful species