Fossil Evidence

• Fossils

  • the preserved remains and traces of past life
  • usually formed in sedimentary rock
  • mostly hard parts of organisms are fossilised - bones, shells, teeth
• Fossil Formation

  • organisms must be protected from decay by micro-organisms
  • must be protected from scavengers
  • need to be buried rapidly
  • lack of 02 in low pH soil is required
  • need to be left undisturbed for a long time
• Fossil Record

  • a chronological list of living things over the history of the earth
  • establishes evolutionary links between species, showing common ancestry
  • provides evidence of which organisms lived on earth in the past
  • provides examples of which organisms may be extinct
  • provides examples of transitional organisms between species
• Fossil Record is Incomplete

  • only a very small % of organisms leave fossilised remains
  • many fossils are destroyed by natural processes - weathering, erosion
  • fossils may be destroyed by human activity
  • fossils may be buried too deep and are unable to be located or accessed
  • archaeologists may be looking in the wrong place
• Principle of Superposition

  • indicates that the oldest layer of rock is found at the bottom, with each layer above being relatively younger
  • relative dating - there's no exact time
• Transitional Forms

  • a fossil which exhibits traits common to both ancestral and derived groups - especially important when groups are sharply differentiated
  • can show how a species may adapt to survive their new conditions
• Fossil Dating Methods

  • relative dating: gives a relative (older/younger) age of fossil - relies on the principle of superposition, older strata are lower down in rock layers
  • absolute dating: gives a numerical (exact/absolute) age of fossil - relies on radioactive decay, decay of isotopes in the fossil or the rock surrounding it
  • both rely on finding fossils of organisms that are no longer alive today
  • both provide evidence for evolution and show how species have changed over time
• Biogeography

  The distribution of organisms and ecosystems across the world and through geologic time