Fossils, Extinction and Speciation

Fossils, Extinction and Speciation

1. Fossils

   • Remains of plants and aniamals
   • From million of years ago
   • Found in rocks
   • How they're formed
     • Gradual replacement by minerals
       • Teeth, shell, bone decay slowly
         • Replaced by minerals as they decay
           • Rock-like substance formed
             • Shaped like original part
               • Surrounding sediments turn to rock
                 • Fossils remain distinct
     • Casts and Impressions
       • Organism buried in soft material
         • Clay hardens around organism
           • Organism decays
             • Cast created
               • Include burrows and roots
                 • Footprints can also leave impressions
     • Preservation
       • In amber and tar pits
         • No O2 or H20
           • Decay microbes can't survive
             • Glaciers are too cold
               • Peat bogs are too acidic

2. Speciation

   • Development of a new species
     • When populations become too different
       • Can't breed to produce fetile offspring
   • Isolation
     • Physically divides a population
       • eg. floods, earthquakes
         • Conditions either side of divide different
           • Natural selection occurs
             • Different characteristics for each population
               • Eventually two populations change too much
                 • So can't produce fertile offspring
                   • Become two separate species
             • Population shows variation - Wide range of alleles
               • Individuals in each population have better characteristics to survive
                 • Better adapted individuals more likely to successfully breed
                   • Alleles controlling beneficial characteristics passed on to offspring
                     • Eventually beneficially characteristic are passed on to an entire new generation

3. Extinction

   • Organisms can't evolve quickly enough
     • Sudden environmental change
     • New predator
       • Humans
     • New disease
     • Can't compete with new species
   • Natural Diaster
     • Volcanic eruption
     • Collision with asteroid
   • New species develops
     • Speciation