Early Earth and the Origin of Life

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Chapter 26 Early Earth and the Origin of Life

• Impact changing life
• Life changes planet
• History and life inseparable

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History of the World part I.
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Introduction to the History of Life

• 3.5 and 4.0 billion years ago. Microscopic and
  unicellular.
• Prokaryotic cells 3.5 billion years found in
  stromatolites. (hydrothermal vents/bacterial
  mats)
• O2 accumulated app. 2.7 bill, years ago,
  photosynthesis by cyanobacteria, dissolved in
  water (oceans), marine sediments in form of iron
  oxide.

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Fossilized Cyanobacteria
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• Eukaryotic cells first found were 1.7 billion
  years old.

• Chloroplasts
• Mitochondrion
• Cellular Respiration

• Multicellular evolved 1.2 bill yrs. ago
• Cell division, cell differentiation
• Limited through early Precambrian age due to ice
  age
• Snowball earth hypothesis life confined to deep
  thermal vents

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• Cambrian Age great diversity formed major groups

• For nearly 90 of its existence, life on Earth
  was confined to aquatic environments.
• Plants and fungi led the way to land about 475
  million years ago.

• Gradual progression. Plants associated with
  fungus.
• Transformed landscape for herbivores etc.

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Origin of life

• Spontaneous generation Life emerged from the
  inanimate.
• Pasteurs Experiments formed Bio-genisis
  theory, Life from life.
• Four Stage hypothesis for Life Formation

1. Abiotic (nonliving) accumulation of small
   organic molecules, or monomers, such as amino
   acids and nucleotides.
2. Joining of these monomers into polymers.(proteins
   and nucleic acids.)
3. Formation of self replicating molecules,
   inheritance possible.
4. Packing these molecules into protobionts

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• Protobionts can Form by Self-Assembly
• Oparin/Haldane theory, Urey/Miller tested

• Laboratory experiments demonstrate that
  protobionts could have formed spontaneously from
  abiotically produced organic compounds. When
  mixed with cool water, proteinoids self-assemble
  into tiny droplets called microspheres.
• These microspheres are coated with a selectively
  permeable protein membrane and undergo osmotic
  swelling or shrinking when placed in solutions of
  different salt concentration.
• The protobionts can discharge a voltage in
  nerve-like fashions such excitability is a
  characteristic of all life. Microspheres are not
  alive, they only display some of the properties
  of life.

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• Produced polymers (proteins, nucleic acids w/o
  enzymes)
• Required hot clay to form.

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RNA may have been the first Genetic Material

• Molecular Replication ribozymes as catalyst.
• Natural Selection, competition for monomers.
• RNA is autocatalytic, capable of ribozyme
  catalyzed replication
• Genotype and phenotype (sequence conformation)

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Self Assembly of Protobionts

• Form spontaneously, liposomes for basic bilayer
• Selectively permeable.
• Membrane potential as energy, discharge as
  electrical impulse.
• Reproduce, simple metabolism

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Natural Selection using inheritable information

• Most successful would grow and split.
• Copies of gene to each (reproduction)
• Mutation/variation occurs
• Evolution differential reproductive success.
• May have led to DNA becoming inheritable.

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Major Lineages of Life

• Two fundamental differences
• Prokaryotes
• Eukaryotes

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The Major Lineages of Life

• Linnaeus divided all know forms of life between
  the plant and animal kingdoms.
• A five Kingdom system.
• 1. Monera Prokaryotic cells.
• 2. Protista All eukaryotic cells that did not
  fit the definition of plant, fungi, or animal.
• 3. Plantae
• 4. Fungi
• 5. Animalia

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Classification Cont.

• An eight-Kingdom system. Prokaryotes are split
  in two Kingdoms, Bacteria and Archaea. Also,
  Protists are split into three Kingdoms,
  Archaezoa, Protista, and Chromista.
• Bacteria (eubacteria)
• Archaea (archeabacteria)
• Archaezoa
• Protista
• Chromista
• Plantae
• Fungi
• Animalia

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Classification Cont.
A Three-domain System
1. Domain Bacteria 2. Domain Archaea 3. Domain
Eukarya (Eukaryotes) 1. Archaezoa 2.
Euglinozoa 3. Alveolata 4. Stramenopila 5.
Rhodophyta 6. Plantae 7. Fungi 8. Animalia