fossils

• • fossils are remains of organisms from many years ago
  • prove that organisms existed bofre
• formed from:

  • gradual replacement - parts of organism that do not decay easily, replaced by minerals
  • casts/impressions - organism buried in soft material that hardens and organism decays, leaving cast
  • preservation - no oxygen or moisture in amber or tar pits, so decay microbes won't survive
  • glaciers - too cold
  • peat bogs - too acidic
• • many early life forms were soft bodied, so, fossil record is incomplete
  • traces left behind mainly destroyed by geological activity
  • so, cannot be certsin about how life began on Earth