Transcript 17-2 Earth’s Early History

The History of Life
Earth’s Early History
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Formation of Earth
Key Concept
Earth’s Early Atmosphere Contained:
Hydrogen Cyanide
Carbon Dioxide
Carbon Monoxide
Nitrogen
Hydrogen Sulfide
Water
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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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Earth’s 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 Continuous
Life 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
1950’s - Chemists
Simulated Earths Early Atmosphere
In 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 & Urey’s 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 Fossils
These 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. 1960’s
–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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