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Fossils are the remains of plants or animals from many years ago. Theyre found in rocks and they provide evidence of how organisms have changed over time. 

Fossils may be formed in various ways:

  • from the hard parts of animals that don't decay easily
  • from parts of organisms that haven't decayed bc one or more of the conditions needed for decay are absent 
  • when parts of the organisms are replaced by other materials as they decay
  • as preserved traces of organisms

Fossils are quite rare bc many early forms of life were soft-bodied & didn't leave traces behind, also bc fossiles have been destroyed by geological activity

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Extinction of Species

The reason for extinction of a species may include:

  • changes to the environment 
  • new predators
  • new diseases
  • new, more successful competitors
  • a single catastrophic event e.g. massive volcano eruptions 
  • the cynical nature of speciation
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New Species

New species arise from a result of isolation 

New species also arise as a result of:

  • genetic variation - each population has a wide range of alleles that control their characterisitcs 
  • natural selection - within each population, the alleles that control the characteristics that hellp the organism to survive are selected
  • speciation - the populations become so different that successful interbreeding is no longer possible 
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