Fossil Preservation Basic

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  • Basics of Fossils
    • Only Hard Parts of Organisms will be Preserved
      • Shells or external skeletons made of calcium carbonate (CaCO3)
      • Internal Skeletons; usually vertebrate bones and teeth made of calcium phosphate
      • Woody material from some plants in the form of lignin
    • Carbonisation
      • This affects organic substances such as lignin and Chitin.
      • During compaction all elements except carbon leave the the plant
        • This creates a black imprint left by the fossil plant.
        • In some rare cases soft body tissue can leave a thin carbon film and preserve more detail than hard parts
    • Petrification  and Replacment
      • This happens as mineral solutions seep through a sediment
        • Sometimes the fossil material is strengthened by the new minerals
        • In some cases the original material is dissolved away and completely replaced by the crystallization         of a new mineral
        • The commonest petrifying and replacing minerals are those that act as cements in sediments.
          • Example:Calcite and Silica
          • In rarer cases fossil material may be replaced by pyrite, haematite or limonite
    • Mould And Cast
      • Organism (hard Parts) buried in sediment and original material dissolves to leave an exact mould of itself
        • New mineral infills mould to produce a cast. Both mould and cast are fossils and each shows detail of original        organism


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