3.2 Fossils and the Evolution of life

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3.2 Fossils and the Evolution of life

• Major stages in evolution of life
• The changing atmosphere
• Other ideas about origins of life

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Outcomes

• Describe key steps in evolution of life,
  including the development of organic molecules,
  membranes, procaryotic and eurcaryotic organisms,
  colonial cells and multicellular organisms
• Identify evidence that present-day organisms have
  evolved from ancestral organisms
• Identify the geological and palaeontological
  evidence that suggests when the earliest life
  forms appeared on Earth
• Explain the importance of the change from an
  anoxic to an oxic atmosphere on the evolution of
  living things
• Outline how scientific knowledge may be in
  conflict with cultural understandings in relation
  to the origins of life

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Major stages in evolution of life

• Formation of organic molecules
• Formation of membranes
• Procaryotic cells (earliest type of fossil found
  no nucleus)
• Eucaryotic organisms( membrane-bound organelles
  and cell organelles
• Colonial cells daughter cells became bound
  together after division eg stromatolites
• Multicellular organisms cells showing
  specialisation within one organisms

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Evolution of organisms

• Starting from present-day diversity, we can trace
  back the evolutionary pathways of living
  organisms
• Some appear to have changed greatly eg horses
• Others did not change over time eg horseshoe
  crab
• Some became extinct eg dinosaur

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Palaeontological and geological evidence of early
life

• Oldest sedimentary rocks on earth are 3800
  million yrs old
• Fossils found in sedimentary rocks Fossil
  evidence in very ancient rocks RARE compared with
  the abundance of fossils found in rocks over the
  600 million yrs
• Earliest fossils 2 typesfound in rocks
  3400-3500 million yrs old in WA, Sth Africa and
  North America
• microfossils (similar to present-day
  single-celled anaerobic procaryotes)
• - Stromatolites layers of photosynthetic
  procaryotic cyanobacteria

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Stromatolites

• Thought to be extinct only fossils found before
  1990s
• 1990s living stromatolites found in Shark Bay,
  WA.
• Cells form a mat which traps
• a layer of sediment.
• Cyanobacteria grow up through the sediment to
  forma new mat layer
• Grow at a rate of about 1mm per year

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Shark Bay, WA Stromatolites present day
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Heterotroph to Autotroph

• 1st primitive cells were heterotrophic
• Cells containing pigments formed .. Able to
  capture light and use it as energy source to make
  organic compounds (photosynthesis)
• This led to massive reduction in carbon dioxide
  and increase oxygen which was taken up by rocks
  oxidised rocks can be seen in ancient banded iron
  and red bed rock formations

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The changing Atmosphere

• All oxidised surface rock saturated with oxygen,
  oxygen began to build up in atmosphere.
• UV radiation reacted with some of it to form
  ozone until a layer formed around earth, high in
  atmosphere
• Shielded earth from UV rays so less reached
  earth decrease in radiation decrease in heat..
  New organisms could form
• Change from anoxic to oxic atmosphere meant that
  anaerobic organisms declined and as oxygen levels
  increases, more photosynthetic organisms
  flourished
• Today, anaerobic organisms can only survive in
  low oxygen / high carbon dioxide environments eg
  mud swamps, bogs, deep underground or in deep
  ocean hydrothermal vents

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Deep ocean hydrothermal vent
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• Oxygen increased, organisms developed that could
  directly use the oxygen aerobic organisms now
  using RESPIRATION
• This allowed increase in their size and
  complexity
• EUCARYOTIC cells evolved, as did multicellular
  plants and animals
• CONDITIONS changed!!!!
• Protection from UV radiation
• Free oxygen in atmosphere
• Liquid water

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Other ideas about origins of life

• Ideas often linked to religious or spiritual
  beliefs of a community/ culture
• Creationism
• Evolution
• Chinese culture Pan Ku 1st living being
• Aboriginal culture Dreaming
• Greek cosmogenies
• Others?