The History of Life

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The History of Life

• Earths Early History

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Picture Credits

• Most Pictures In This PowerPoint Were Downloaded
  From

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Formation of Earth

• Key Concept
• Earths Early Atmosphere Contained
• Hydrogen CyanideCarbon DioxideCarbon
  MonoxideNitrogenHydrogen SulfideWater

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Formation of Earth

• The Material Forming Earth Probably Condensed
  From Stellar Debris Over 100 Million Years
• Surface Originally Molten
• Atmosphere Pinkish-Orange

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Condensation of Debris
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Earths Early Atmosphere
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Formation of Earth

• 4 Billion Years Ago Earth Cooled Enough For A
  Crust To Form
• Volcanic Activity Constant
• Comet Asteroid Hits Constant
• Kept Earth Hot

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Early Crust Forms
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Formation of Earth

• 3.8 Billion Years Ago
• Earth Cooled Enough
• For Water To Condense
• Oceans Formed
• Green/Brown With Iron
• Thunderstorms ContinuousLife Appeared

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The First Organic Molecules

• Atoms Do Not Assemble Into Complex Organic
  Molecules Today Due To
• Oxygen is VERY Reactive
• Bacteria would eat them

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Miller Urey

• Stanley Miller Harold Urey
• 1950s - Chemists
• Simulated Earths Early AtmosphereIn The
  Laboratory
• Ran Electric Sparks Through It Simulating
  Lightning

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Miller Urey

• Experiment Generated Amino Acids In Just A Few
  Days

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Miller Urey

• Key Concept
• Miller Ureys Experiments Suggested How
  Mixtures Of The Organic Compounds Necessary For
  Life Could Have Arisen From Simpler Compounds
  Present On A Primitive Earth.

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Modified Miller Urey

• Original Atmospheric Components Not
  Accurate(Re-Analysis of Chemical Composition of
  Early Rocks)
• Corrected Experiments Have Produced Cytosine
  Uracil
• Two RNA Bases

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How Did Life Begin?

• How Did Life Form From The Organic Soup Of
  Original Earth?
• Prokaryote FossilsThese Fossils Date To 200-300
  Million Years After The Earth Cooled Enough For
  Water To Form

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Formation of Microspheres

• Proteinoid Microspheres
• Large Organic Molecules Naturally Form Tiny
  Bubbles
• Not Cells But Have Some Characteristics Of Living
  Systems
• e.g. Selective Permeable Membranes

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Evolution of RNA DNA

• Still Unknown However
• RNA Sequences Have Been Found That
• Help DNA Replicate
• Transcribe DNA
• Translate Proteins
• Catalyze Chemical Reactions
• Duplicate Themselves
• Perhaps RNA Came First

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Free Oxygen

• Microfossils - 3.5 Billion Years Old
• Prokaryotes
• Anaerobic (No O2 In Atmosphere)
• Photosynthetic Bacteria Arose
• 2.2 Billion Years Ago
• O2 Continuously Released Into The Atmosphere

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Free Oxygen

• First It Bound Iron In The Oceans
• Iron Oxides Settled To The Bottom Of The Oceans
• Formed Great Bands Of Iron That We Mine Today
• Oceans Changed Turned Blue

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Free Oxygen

• Next O2 Accumulated In The Atmosphere
• O2 Increased
• Methane Hydrogen Sulfide Decreased
• Atmosphere Turned Blue

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Free Oxygen

• Is Highly Reactive
• Deadly To Anaerobes
• First Aerobic Organisms Arise

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Free Oxygen

• Key Concept
• The Rise Of Oxygen In The Atmosphere Drove Some
  Life Forms To Extinction, While Other Life Forms
  Evolved New, More Efficient Metabolic Pathways
  That Used Oxygen For Respiration

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Variations in CO2 and O2
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Variations in CO2 and O2
C Cambrian O Ordovician S Silurian D
Devonian C Carboniferous P Permian Tr
Triassic J Jurassic K Cretaceous T
Tertiary 0 on time scale Today
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Origin of Eukaryotic Cells

• Began About 2 Billion Years Ago
• Some Prokaryotes Started Developing Inner Cell
  Membranes

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Origin of Eukaryotic Cells

• Endosymbiotic Theory
• Some Smaller Prokaryotes Began Living In Larger
  Prokaryotes. A Symbiotic Relationship Developed
• Some Became Mitochondria
• Some Became Chloroplasts

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Origin of Eukaryotic Cells

• Key Concept
• The Endosymbiotic Theory Proposes That Eukaryotic
  Cells Arose From Living Communities Of
  Prokaryotic Organisms
• First Proposed 100 Years Ago

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Origin of Eukaryotic Cells

• Lynn Margulis Boston U. 1960s
• Evidence
• Mitochondria Chloroplasts Contain DNA
  Ribosomes Similar To Bacterial DNA Ribosomes
• They Reproduce By Binary Fission

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Sexual Reproduction Multicellularity

• Shortly After Forming Multicellular Organisms
  Sexual Reproduction Began
• Accelerated Development of Genetic Variation
• A Few Hundred Million Years Later, Multicellular
  Organisms Arose And Exploded

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