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Evidence for Evolution

  • The remains of hard parts (eg. bones, shells) of the animal after the soft parts have decayed from fossils
  • Insects may occasionally get trapped in amber or a similar material, so dont decay as the microbes cannot respire in the material
  • This results in a complete carcass of the insect, though this is very rare
  • Evidence of an organism- imprints, footprints etc. can also be preserved

The Process:

  • The organismdies and falls into soft mud or silt, often at the bottom of a lake
  • The body is buried in silt/ mud
  • The silt/ mud gradually turn to rock, encasing the dead body
  • The hard parts of the organism are replaced
  • The soft parts dont form fossils because they decay quickly
  • If earth movements make the land rise, the fossils may be uncovered

Scientists are not certain as to how the Earth started as there are no fossils or other evidence to prove or disprove anything

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Causes of Extinction

Changes to the Enviroment:

  • Changes in climate or weather mean that their habitat is destroyed and the species cannot adapt to the new area
  • Eg. Wooly Mammoth

Major Catastrophic events: Eg. An asteroid/ meteor stopped sunlight entering the atmosphere so the plants couldnt grow so the dinosaurs couldnt eat

New Diseases:

  • New diseases which organisms arent adapted to kill them
  • Eg. Golden toad

New Predators: Eg. Humans started hunting dodos so they became extinct

New Competitors:

  • A bigger/ stronger species may take the food or habitat of the first species so they cannot breed or eat
  • Eg. Grey squirrels were better at finding food so red squirrels have declined
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Extinct: When there are no living members of a species

Species: A group of organisms which look and behave similarly and which can breed to produce fertile offspring

The Process:

  • Isolation- The original species is split up to be in 2 different places
  • Genetic variation- Some members of the species become mutated
  • Different Conditions- The better adapted individuals survive & breed
  • The mutated alleles are passed on to the next generation
  • Eventually, the genetics of the two species mean that they cannot breed together
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