Paleontology

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How did life originate?

• Old hypothesis Organic soup
• Inorganic chemicals like methane, carbon dioxide
  and ammonia may have been present in Earths
  early atmosphere
• Solar radiation, lightning, etc. triggered
  chemical reactions which formed amino acids
  organic soup
• Amino acids are the building blocks of proteins
  the basic stuff of life

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Miller Urey Experiment

• No longer considered valid
• No evidence that this was the early composition
  of the atmosphere
• Some evidence to suggest an oxygen-deficient, but
  otherwise modern atmosphere

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Possible Sites for the Origin of Life

• Tidal Pools
• Clay
• Pyrite
• Bubbles
• Hot springs/Hydrothermal Vents

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Newer Idea

• Life may have originated near hot springs and
  volcanic vents
• Heat supplied the energy for life processes
• Energy also available from chemical reactions

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Organisms around a modern black smoker vent
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Earliest Life Prokaryotes

• Prokaryotes cells with no nucleus
• Single cells
• Strings of cells
• Mats of cells - Stromatolites

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Earliest Life Prokaryotes
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Cyanobacteria 3.46 Ga
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Modern Stromatolites
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Stromatolites
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Extraterrestrial Origins of Life?

• Ingredients in comets
• Evidence from meteorites
• Could life have been transplanted to Earth from
  an extraterrestrial source?
• Did life arise on Earth and other planets
  simultaneously?

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Magnetite from Martian Meteorite evidence of
bacteria?
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The Allan Hills MeteoriteBacteria(?) from Mars
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Life in Stasis 3 Ga of Single Cells

• Life begins approximately 4.0 Ga
• 3.8 Ga first stromatolites
• 3.46 Ga filaments of cyanobacteria
• 1.9-1.7 Ga at least 12 species of prokaryotes
• 1.0 Ga first eukaryotes
• 0.9 Ga (900 Ma) sexual reproduction
• 600 Ma first multicellular organisms

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The Ediacaran BiotaEarliest Multicellular Life