Evolution of Life on Earth

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Evolution of Life on Earth

• Melissa Harker

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Prokaryotes-first life form

• We are closer to archaea than prokaryota (16s
  rRNA)
• 3.8 billion years ago bacteria emerged, then
  oxygen-producing bacteria
• Stromatolites and cyanobacteria evolved later
• After 2.5 bya, increase in oxygen changed life
  forms...algae, etc.

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Primitive eukaryotes

• After protista, primitive worm-like creatures
  appeared
• Sponges, cnidaria appreared, trilobites-first
  arthropod

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Edicaran Fauna

• Similar to jellyfish, no hard parts to make good
  fossils
• 635-642 Ma

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Cambrian explosion (540 Ma)

• A result of the rise of oxygen?
• Chordates (will explain later)
• Most organisms from this period, trilobites, etc.
  died off
• First vascular plants from algae, then ferns,
  then seed plants, gymnosperms, finally
  angiosperms
• Ferns do not evolve into seed plantsthey are an
  evolutionary dead end!

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Primary Chordates

• Jawless fish-most primitive
• Hagfish have no backbone, lampreys do
• Lungfish actually were not well-adapted,
  advanced fish
• The Coelacanth is not the ancestor of amphibians

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Amphibians

• Evolved from a relative of the coelacanth
• Key structure to life on land is the amniotic egg
  that reptiles, birds, and mammals have

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Reptiles

• Turtles closest to crocodiles genetically
• Birds evolved from dinosaurs

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Mammals

• Did not evolve from birds, even though the first
  mammals laid eggs.
• They are a separate spin off
• Marsupials evolved before placentals

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