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  • How they are formed
    • Fossils
      • How life on Earth was formed
        • Scientists can't be sure how life began - lack of valid evidence as fossil record is incomplete
        • Many early life forms were soft bodied so they left few traces behind
        • Primordial soup theory
          • Involves interaction between methane, ammonia, hydrogen and lightening in the early atmosphere
            • Thought that lightening could have caused a chemical reaction between gases, resulted in the formation of amino acids
              • Amino acids are the building blocks for proteins, the amino acids could then have combined to form organic matter in the primitive oceans
    • From hard part of animals that don't decay easily - bones and shells
    • From parts of organisms that have not decayed because the conditions for decay are absent
      • When parts of the organism are replaced by minerals as they decay - forms a rock-likeb substance in the shape of the dead remains
        • As preserved traces of organisms - may become covered by sediments, form rocks over millions of years


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