Fossils

• Fossils


  Things left by long-dead organisms
• Fossils


  • Important as most things that lived are extinct - look at what they left
  • Evidence for how organisms changed (evolution)
• Main ways fossils are formed

  • Gradual replacement by minerals (e.g. shells, teeth, bones)
  • Casts & impressions (formed when organisms are buried in material like clay)
  • Preservation (no decay at all, e.g. organisms stuck in tar pits, ice glaciers, peat bogs)
• Oldest fossils are 3.5-4 billion years old
• No complete fossil record - early life forms may have been too soft-bodied and fossils formed may have been destroyed (e.g. by volcanoes, earthquakes, tectonic plates)
• Extinction


  No individuals of that species remain
• Reasons for extinction


  • Environmental changes (e.g. too warm, habitat cut down)
  • New predator/disease
  • New species out-competes them
  • Catastrophic event (e.g. asteroid)