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  • Fossils
    • Formed from Gradual Replacement by minerals
      • 1)Things like teeth, shells, bones etc, which don't decay easily, can last a long time when buried
      • 2)They're eventually replaced by minerals as they decay, forming a rock like substance
      • 3)The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up
    • Formed from Casts and Impressions
      • 1)Sometimes fossils are formed when an organism is buried in a soft material like clay
      • 2)The clay hardens around it and the organism decays, leaving a cast of itself
      • 3)Things like footprints can be pressed into these materials when soft, leaving an impression when it hardens
    • Formed from Preservations in places where no decay happens
      • 1)In amber and tar pits there's no oxygen or moisture so decay microbes can't survive
      • 2)In glaciers its too cold for the decay microbes too work
      • 3)Peat bogs are too acidic for decay microbes
    • No one knows how life began
      • There are various hypotheses suggesting how life came into being
      • These hypotheses can't be supported or disapproved because there's a lack of valid and reliable evidence


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