GCSE A* REVISION NOTES


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B2.8: Speciation

Fossil – The mineralised remains or impressions of prehistoric organisms

There are several types of fossils:

Formation of Fossils

  1. Organism is alive
  2. Organism dies
  1. Soft parts rot away
  1. Hard remains get covered by sediment
  2. Hard parts get replaced by minerals
  1. Layers of sediment are compressed over time forming sedimentary rock
  2. Rocks are moved and liberated by geological processes
  3. Rock is worn away over time
  1. Fossil is discovered

Fossil Record

The Horse

Incomplete fossil record

Extinction

Causes for extinction

Mass extinction

 

Theories for the extinction of the dinosaurs
Evolution
Out competed/non-adapting
Climate Change
Palaeocene Theory
Disease
Asteroid Strike

 

 

Species

A group of organisms which are able to reproduce successfully to produce fertile offspring

Australia

Speciation

  1. A population of the same species is geographically isolated
  2. There are different selective process in different areas
  3. Different alleles are selected in different areas
  4. Individuals with the advantageous alleles outcompete the other individuals
  5. The more competitive individuals reproduce more and pass the advantageous alleles on to more offspring
  6. The different populations evolve differently to become two genetically distinct species
  7. If the two species come back together they will not be able to reproduce

e.g. Californian Salamander

 


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