Fossils and Speciation

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  • Created by: Sophie
  • Created on: 10-05-13 15:57

Fossils

  •  fossils form in rocks in three ways:
    • gradual replacement-bones, shells, teeth etc don't decay easy, get buried, replaced by minerals forming rock-like substances shaped like original part, surrounding sediment turns to rock
    • casts- organism is buried in soft material, material hardens, organisms decay, leaving a cast 
    • impressions- things like footprints pressed into soft materials, materials harden leaving an impression of the print
    • preservation- in places where no decay happens due to unsuitable conditions for decay microbes so they cant survive e.g. amber and tar pits-no oxygen, glaciers-too cold and peat bogs-too acidic
  • fossil record not complete because: 
    • early organisms were soft-bodies, soft tissue decays completely
    •  fossils destroyed by geological activity e.g movement of tectonic plates crushed fossils
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Extinction

  • term species means organisms that can breed together to give fertile offspring 
  • species that don't exist anymore are extinct
  • reasons:
    • environmental changes 
    • new predator
    • new disease 
    • another species is more successful
    • catastrophic event 
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Speciation

  • speciation=development of a new species
  • occurs when populations of same species become so different they cant breed successfully anymore 
  • isolation-population of species separated e.g by geographical barrier, conditions either side are different so different characteristics will become more common in each population due to natural selection:
    • variation because of wide range of alleles
    • most suited characteristics to the environment=best chance of survival=more likely to breed so get passed on to the next generation
  • eventually the separated populations become so different they cant breed so they are different species
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