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    • Evidence for early forms of life come from fossils
    • Fossils are the remains of organisms from many years ago and are found in rocks
  • dead organisms usually decay
    • hard parts don't decay easily
      • Hard parts fossilise, e.g. bones and teeth
    • conditions don't allow decay e.g. not enough oxygen
      • Soft tissues also fossilise e.g. leaf, muscle tissue, animals with no hard parts
    • parts of organisms replaced by other materials as they decay
  • traces of organisms, e.g. footprints, burrows, rootlet traces
    • fossilise in special conditions, e.g. as casts in mud
    • The age of a fossil can be worked out from the age of the rock it's in.
      • This can show how much or how little organisms have changed over millions of years
    • The fossil record is not complete because:
      • fossils only form in special conditions
      • many early life forms had soft bodies that left few traces
      • geological changes in rocks destroy some fossils


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