1. The Origin and Early History of Life
Chapter 4
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2. Origin of Life Theories Chemical Evolution Cell Origination Theories
Outline
Properties of Life
Origin of Life Theories
Chemical Evolution
Cell Origination Theories
Earliest Cells
Eukaryotic Cells
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3. Properties of Life (review)
Made of cells
Reproduce
Genetic Code
Grow and Develop
Require energy, water and other materials
Respond to stimuli
Maintain homeostasis (stable internal conditions)
Move
Adapt (change over time)
Require water
Die
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4. Origin of Life Theories
Special Creation
Oldest and most widely accepted hypothesis.
Extraterrestrial Origin
Panspermia - Cosmic material may have carried complex organic molecules to earth.
Spontaneous Origin
Life evolved from inanimate matter.
Most scientists tentatively accept this theory
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5. Amino acids would therefore not last long.
Where Life Started
One assumption about the early atmosphere was a reducing atmosphere of carbon dioxide, nitrogen gas, and water vapor, but very little oxygen.
Amino acids would therefore not last long.
Atmosphere would have changed with the advent of photosynthesis.
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6. Potential Sites of Origin Ocean’s Edge Under Frozen Seas
Where Life Started
Potential Sites of Origin
Ocean’s Edge
Under Frozen Seas
Deep in Earth’s Crust
Clay
Deep Sea Vents
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7. Miller-Urey Experiment
Stanley Miller and Harold Urey (1953) attempted to reproduce conditions at the ocean’s edge under a reducing atmosphere.
Were able to form amino acids with the addition of lightning to a reducing atmosphere rich in hydrogen and devoid of oxygen.
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8. Raven - Johnson - Biology: 6th Ed
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9. Debated if RNA or Proteins evolved first.
Chemical Evolution
Debated if RNA or Proteins evolved first.
RNA Group believes other complex molecules could not have been formed without a heredity molecule.
Protein Group argues that without enzymes, replication would not be possible.
Peptide-Nucleic Acid Group believes peptide nucleic acid was precursor to RNA.
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10. Alexander Oparin - Primary abiogenesis.
Cell Origin Theories
Ocean Edge Scenarios
Bubble Theory - Bubble structure shielded hydrophobic regions of molecules from contact with water.
Alexander Oparin - Primary abiogenesis.
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11. Raven - Johnson - Biology: 6th Ed
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12. Physically resemble bacteria. Prokaryotes - Lack nucleus (bacteria)
Earliest Cells
Microfossils - Earliest evidence of life appears in fossilized forms of microscopic life.
Physically resemble bacteria.
Prokaryotes - Lack nucleus (bacteria)
Eukaryotes - Contain nucleus (all other living things)
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13. DNA sequences are very different from all other living things
Earliest Cells
Archaebacteria - Ancient bacteria that live in extremely hostile conditions.
DNA sequences are very different from all other living things
Lack peptidoglycan in cell walls.
Have unusual lipids in cell membranes.
Methanogens
Anaerobic
Halophiles
Thermophiles
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14. Eubacteria - Second major bacterial group.
Earliest Cells
Eubacteria - Second major bacterial group.
Contain very strong cell walls and simpler gene architecture.
Cyanobacteria
Photosynthetic
Appeared at least 3 bya.
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15. First Eukaryotic Cells
First appeared about 1.5 bya. (maybe earlier)
Possess internal nucleus.
Endoplasmic Reticulum - Network of internal membranes in eukaryotes.
Both Endoplasmic Reticulum and nuclear membrane are believed to have evolved from infolding in outer bacterial membranes.
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16. Raven - Johnson - Biology: 6th Ed
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17. Mitochondria and Chloroplasts
Endosymbiotic Theory suggests a critical stage in the evolution of eukaryotic cells involved endosymbiotic relationships with prokaryotic organisms.
Energy-producing bacteria may have come to reside within larger bacteria, eventually evolving into mitochondria.
Photosynthetic bacteria may have come to live with larger bacteria, eventually forming chloroplasts in plants and algae.
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18. Copyright © McGraw-Hill Companies Permission
required for reproduction or display
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