Ch. 26 - Early

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Ch. 26 - Early Earth The Origin of Life
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• Major Events in Evolution
• 4.6 bya formation of the Earth (Precambrian)
• 3.5 bya prokaryotic cells
• 2.2 bya eukaryotic cells
• 600 mya soft-bodied invertebrates
• 500 mya colonization of land plants (Paleozoic)
• 420 mya jawless fish
• 375 mya bony fish, amphibians, insects
• 325 mya first seed plants, reptiles
• 220 mya cone-bearing plants (Mesozoic)
• 175 mya dinosaurs abundant
• 80 mya angiosperms
• 60 mya mammals, birds, pollinating insects
  (Cenozoic)
• 30 mya primate groups
• 2.5 mya apelike ancestors
• 0.5 mya humans appear

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Major Events in Evolution
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Life on Earth Between 4.0 and 3.5 Billion Years
Ago

• The planet was bombarded with by
  huge rock bodies left over from the
  formation of the solar system.
• One of them may have dislodged a chunk of Earth
  that became the moon.
• The pounding may have generated enough heat to
  vaporize all the available water
  and prevent seas from forming.
• As Earth began to cool and liquid
  water could exist, prokaryotic life
  appeared.

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Life on Earth Between 3.5 and 2.0 Billion Years
Ago

• The fossil record supports that
  prokaryotes were the first
  organisms on the planet.
• Two main evolutionary branches to the prokaryotes
  existed that still exist today, bacteria and
  archaea.

Fossilized Ancient Bacterium Living
Leptolyngbya Bacterium
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Oxygen Began Accumulating in the Atmosphere About
2.7 Billion Years Ago

• The only photosynthetic prokaryotes that generate
  oxygen are called cyanobacteria.
• The free oxygen probably dissolved in the
  surrounding water until the seas and lakes became
  saturated with the oxygen.
• Once the dissolved iron precipitated from the
  water as iron oxide, O2
  began to gas out of the
  water and accumulate in
  the atmosphere.

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Eukaryotic Life Began By 2.1 Billion Years Ago

• The oxygenation of the atmosphere coincides
  with the evolution of eukaryotic cells.
• With the evolution of eukaryotic cells came
  chloroplasts and mitochondrion.

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Multicellular Eukaryotes Evolved By 1.2 Billion
Years Ago

• As eukaryotic single-celled
  organisms flourished, they gave
  rise to a diversity of protists.
• Multicellular eukaryotes also evolved and gave
  rise to modern day algae, plants, fungi, and
  animals.

Fossilized Animal Embryo
Fossilized Algae
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Animal Diversity Exploded During the Early
Cambrian Period

• 600 mya First invertebrate
  animals appear porifera
  (sponges)
• 543 mya First cnidarians jellyfish and hydra

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Plants, Fungi, and Animals Colonized the Land
About 500 Million Years Ago

• Challenges that organisms face
  as they move from life in the
  water to life on land include preventing the
  loss of water and reproducing on land.
• Plants had to develop root systems to anchor
  themselves and take up water and nutrients.
• Plants also developed a cuticle to prevent water
  loss.

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Plants, Fungi, and Animals Colonized the Land
About 500 Million Years Ago

• The most widespread and diverse land animals are
  the arthropods (mostly insects and spiders)
• The land vertebrates, or tetrapods, evolved from
  marine fishes
• Amphibians evolved from fishes
• Reptiles evolved from amphibians
• Both birds and mammals evolved from reptiles
• Most groups of modern mammals were established
  about 50 - 60 mya including primates
• The human lineage diverged from other primates
  only 5 mya

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The Origin of Life

• Biogenesis life arises only by the reproduction
  of preexisting life Pasteurs experiment proved
  this.

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The Origin of Life How Can Life Arise From
Nonliving Matter?

• Hypothesis for the origin of life
• The abiotic synthesis of small organic molecules,
  such as amino acids and nucleotides
• The joining of these small molecules (monomers)
  into polymers, including proteins and nucleic
  acids
• The origin of self-replicating molecules that
  eventually made inheritance possible
• The packaging of all these molecules into
  protobionts, droplets with membranes that
  maintained an internal chemistry different from
  the surroundings.

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Hypothesis For The Origin Of Life

• Oparin and Haldane independently hypothesized in
  the 1920s that the early atmosphere was probably
  a reducing atmosphere (electron adding) because
  there was less oxygen
• In order for organic
  molecules to be
  produced, considerable
  energy must be
  provided lightning and
  intense UV radiation
  could provide this
  energy

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Hypothesis For The Origin Of Life

• In 1953, Stanley
  Miller and Harold
  Urey tested the
  Oparin-Haldane
  hypothesis
• They were able to
  produce a variety
  of amino acids and
  other organic
  compounds found
  in living
  organisms
  today

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Hypothesis For The Origin Of Life

• RNA may have been the first genetic material
• Short polymers of ribonucleotides have been
  produced abiotically in lab experiments
• RNA molecules act as catalyst in modern cells and
  may have been the first enzymes (ribozymes)
• RNA could have provided the template on which DNA
  nucleotides were assembled
• Once DNA appeared, RNA molecules would have begun
  to take on their modern roles

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The Five-Kingdom System

• Whittakers five-kingdom system (1969)
• Classified living things on the basis of cell
  type and nutrition

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The Three-Domain System