Fossils, Extinction and Speciation

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Biology GCSE Unit 2 Fossils, Extinction and Variation
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Fossils, Extinction and Speciation
  1. Fossils
    1. Remains of plants and aniamals
      1. From million of years ago
        1. Found in rocks
          1. How they're formed
            1. Gradual replacement by minerals
              1. Teeth, shell, bone decay slowly
                1. Replaced by minerals as they decay
                  1. Rock-like substance formed
                    1. Shaped like original part
                      1. Surrounding sediments turn to rock
                        1. Fossils remain distinct
              2. Casts and Impressions
                1. Organism buried in soft material
                  1. Clay hardens around organism
                    1. Organism decays
                      1. Cast created
                        1. Include burrows and roots
                          1. Footprints can also leave impressions
                2. Preservation
                  1. In amber and tar pits
                    1. No O2 or H20
                      1. Decay microbes can't survive
                        1. Glaciers are too cold
                          1. Peat bogs are too acidic
              3. Speciation
                1. Development of a new species
                  1. When populations become too different
                    1. Can't breed to produce fetile offspring
                  2. Isolation
                    1. Physically divides a population
                      1. eg. floods, earthquakes
                        1. Conditions either side of divide different
                          1. Natural selection occurs
                            1. Different characteristics for each population
                              1. Eventually two populations change too much
                                1. So can't produce fertile offspring
                                  1. Become two separate species
                              2. Population shows variation - Wide range of alleles
                                1. Individuals in each population have better characteristics to survive
                                  1. Better adapted individuals more likely to successfully breed
                                    1. Alleles controlling beneficial characteristics passed on to offspring
                                      1. Eventually beneficially characteristic are passed on to an entire new generation
                    2. Extinction
                      1. Organisms can't evolve quickly enough
                        1. Sudden environmental change
                          1. New predator
                            1. Humans
                            2. New disease
                              1. Can't compete with new species
                              2. Natural Diaster
                                1. Volcanic eruption
                                  1. Collision with asteroid
                                  2. New species develops
                                    1. Speciation
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