Early Earth and Origin of Life

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Early Earth and Origin of Life

• Chapter 26

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• Earths original organisms are microscopic and
  unicellular.
• Life on Earth originated b/w 3.5- 4 billion years
  ago.
• Earth formed 4.5 billion years ago.
• Evidence of ancient prokaryotes found in rocks
  called stromatolites- banded domes of sedimentary
  rock similar to layered mats formed today in salt
  marshes and some warn ocean lagoons by colonies
  of bacteria and cyanobacteria. The layers are
  sediments that stick to jelly-like coats of
  motile microbes, which continually migrate out of
  one layer of sediment and form a new one above,
  producing the banded pattern

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Major episodes in the history of life

• 1. Origin of Earth
• 2. Earth cool enough for crust to solidify
• 3. Origin of life (prokaryotes)
• 4. RNA sequence data shows prokaryotes split
  into 2 groups bacteria and archae
• 5. Production of oxygen by early photosynthetic
  prokaryotes create aerobic atmosphere, and
  organisms must adapt to being aerobic, and
  species set to evolve
• 6. Origin of eukaryotes protists- large,
  disparate group of unicellular eukaryotes and
  some closely related multicellular organisms
• 7. Origin of multicellular organisms Plant,
  fungi, and animals. (fungi more related to
  animals than plants) in PreCambrian
• 8. Late PreCambrian oldest animal fossils
• 9. Plants and symbiotic fungi colonize land
  Paleozoic
• 10. Extinction of Dinosaurd at end of Mesozoic
• 11. First humans at end of Cenozoic

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First organisms were products of chemical
evolution in 4 stages

• 1. The abiotic (nonliving) synthesis and
  accumulation of small organic molecules
  (monomers) such as amino acids and nucleotides
• 2. Joining of these monomers into polymers
  (proteins and nucleic acids)
• 3. Aggregation of abiotically produced molecules
  into droplets (protobionts) that had chemical
  characteristics different from surroundings.
• 4. Origin of heredity (before droplet stage)

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Oparin-Haldane Hypothesis

• In the present atmosphere, oxygen is rich and
  attach chemical bonds, extracting electrons.
  Before oxygen producing photosynthesis, Earth had
  a much less oxidizing atmosphere. Such a reducing
  (electron adding) atmosphere would have joined
  simple molecules to form complex ones. This
  requires a lot of energy, possible provided from
  lightning, intense UV radiation, and volcanic
  vapors from the atmosphere back then. Today, the
  oxygen has produced an ozone layer that prevents
  UV radiation.

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Stanley Miller and Harold Urey

• They tested Oparin-Haldane hypothesis by creating
  experiment similar to Earths early atmosphere
  used an apparatus where a warm flask of water
  represented the sea. The atmosphere had
  (H20-water, H2-hydrogen, CH4-methane, and
  NH3-ammonia). Sparks were discharged in the fake
  atmosphere to mimic lightning. A condenser cooled
  the atmosphere, raining water and other dissolved
  compunds back to the sea. As material circulated
  through the apparatus, the solution in flask
  turns clear? murky brown. After one week, variety
  of organic compounds including amino acids that
  make up proteins of organisms, were found.

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Protobionts

• Living cells may have been preceded by
  protobionts (abiotically produced molecules)-
  cannot reproduce, but maintain internal
  environment diff. from surroundings and exhibit
  some properties similar to life such as
  metabolism and excitability.
• Coacervate (a protobiont) is a stable droplet
  that tends to self-assemble when a suspension of
  macromolecules is shaken. Hydrophobic
  macromolecules surround coacervate, which absorb
  substrates from enzymes and release products of
  reactions catalyzed by the enzymes.

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• Protobionts could have formed spontaneously from
  abiotically produced organic compounds
• Microspheres made by cooling solutions of
  proteinoids (polypeptides created abiotically
  from amino acids polymerized on hot surfaces).
  Microspheres grow by absorbing free proteinoids
  until they reach unstable size, and split to form
  daughter microspheres.
• In aqueous environ., certain lipids self-assemble
  to form liposomes, which some grow by engulfing
  smaller liposomes and then splitting, other times
  giving birth to smaller liposomes.

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RNA is first genetic material

• RNA is autocatalytic, and in prebiotic world, RNA
  molecules capable of self-replication
• RNA acts as template for making polypeptides and
  in turn the polypeptides act as enzymes that aid
  in the replication of RNA molecules.
• Within a membrane, polypeptides aid the
  replication of only the template RNA genes.

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Were RNA or DNA genes preceded by simpler
hereditary systems?

• Amino-adenosine triacid ester (AATE) , consists
  of amino adenosine and an ester.
• AATE can catalyze synthesis of another AATE by
  acting as a template.

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THE END

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