The Origins of Life - PowerPoint

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					         The Origins of Life

• The Big Bang occurred about 18 billion
  years ago, creating the universe.
• The Earth formed about 4.6 billion years
  ago.
• Life on Earth probably originated between
  3.5 and 4 billion years ago.
         Evidence of First life
            Stromatolites
• Stromatolites are
  mounds of banded
  sediment formed by
  mobile cyanobacteria.
• They are found in the
  warm waters of
  Australia and off the
  coast of Baja, Mexico.
Evidence of First Life
    Stromatolites
           • Stromatolites have
             been found that date
             back to 3.5 billion
             years ago.
           • They are strikingly
             similar to those
             produced by modern
             day bacteria.
         Evidence of First Life
               Fossils
• Fossilized filamentous
  bacteria has also been
  found that dates back
  to 3.4 billion years.
• This fossilized
  prokaryote was found
  in a 3.4 billion year
  old stromatolite in
  Western Australia.
               Early Earth
• When the Earth first formed, it was very
  different from its current state.
• It was filled with reducing gases, like H2,
  NH3, CH4, CO, and CO2.
• Most notably, the atmosphere of early Earth
  was completely anaerobic.
• It lacked a protective ozone layer.
            Chemical Origins
• In the 1920’s, Oparin
  and Haldane predicted
  that the conditions of
  early Earth favored the
  spontaneous formation
  of organic compounds.
• In 1953, Miller and
  Urey tested this
  hypothesis.
      From Molecules to Cells
1. Small organic monomers formed in
   reducing atmosphere.
2. Monomers joined to form polymers –
   binding sites in clay helped concentrate
   the monomers, while metal ions acted as
   catalysts.
3. Polymers aggregated to form protobionts.
4. A molecule of heredity originated.
Protobionts
      • Protobionts are
        aggregates of molecules
        that have some cell-like
        qualities such as:
         – Self-assembly
         – Response to osmotic
           forces
         – Ability to store a
           membrane potential
         – Engulfing and splitting
                   First Life
• Prokaryotic
• RNA as genetic material
• Heterotrophic – absorbed organic molecules from
  surroundings
• Anaerobic – oxygen was not present in
  atmosphere until it was put there by
  photosynthetic bacteria as a waste product (began
  accumulating about 2 billion years ago
       Origin of photosynthesis
• Some time after the first living things appeared,
  cells developed that could perform photosynthesis.
• These organisms put oxygen into the air as a waste
  product.
• About 1.5 billion years ago, oxygen still only
  made up about 1% of the atmosphere
• Accumulation of oxygen in the atmosphere is
  thought to have ended chemical evolution
             Open for debate
• Some scientists believe organic molecules came to
  Earth from outer space. Meteors have been found
  containing amino acids and nucleic acids
  (including several amino acids nonexistent on
  Earth).
• There may have been a simpler hereditary
  molecule that preceded RNA, or maybe RNA was
  never genetic material.
• Maybe life began near hydrothermal vents (and
  still forms there?)
Taxonomy – the classification of
       living things
• From that first cell,
  life has diversified
  into millions of
  different forms.
• These forms are
  divided into five major
  kingdoms: Animalia,
  Plantae, Fungi,
  Protista, and Monera.

				
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posted:7/27/2012
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