Geologic History of the Earth

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Geologic History of the Earth
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Star Formation begins with a nudge
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Formation of the Solar System
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Planetary accretion
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Why terrestrials and Jovians?
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Terrestrial Composition
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Jovian Composition
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Leftover Debris
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Kuiper Belt
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Oort Cometary Cloud
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Formation of the Moon (4.5 BYA)
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Structure of the Earths Interior
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Early Bombardments

• Heaviest impacts lasted 100 million years
• Tapered off 3.5 billion years ago
• Evidence?
• Impacts still occur today

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Cratered Worlds
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Formation of the Oceans and Atmosphere

• Earth was not formed with atmosphere
• Gasses brought by planetesimals
• Outgassing and impacts released gasses
• H20 CO2 N2 H2S SO2
• Water vapor condensed to form oceans
• Oceans were in place 4.3 4.4 BYA

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Earths Primitive Atmosphere

• Produced by outgassing
• Formed 4.3 4.4 billion years ago?
• Rich in hydrogen, carbon, nitrogen, oxygen
• CO CO2 N2 H2O some H H2
• Contained complex molecules from ISM
• Hydrogen lingered for a few million years

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Atmospheric Retention
photodissociation

• Molecular velocity

Planetary Escape Velocity
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Evolution of the Earths Atmosphere

• Oxygen Levels Currently 21
• 2-2.3 billion years ago
• Photosynthesis
• Originally oxidation kept pace with oxygen
  production (CO ? CO2, rust)
• Evolution of large plants, trees, flowers,
  grasses (600 MYA)

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Creation of Ozone (O3)

• O2 UV ? O O
• O O2 ? O3
• Requires the absence of hydrogen
• Significantly increased 600 MYA
• Ozone allowed life to venture onto land

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Evolution of the Earths Atmosphere

• Nitrogen Levels Currently 78
• Liberated by outgassing
• Significance of denitrifying bacteria
• Atmospheric nitric oxide (NO) ? rain ?
  soil/oceans ? bacteria ? atmosphere

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Evolution of the Earths Atmosphere

• Argon Currently 1
• Inert formed by radioactive decay of potassium
• Liberated by outgassing

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Evolution of the Earths Atmosphere

• Carbon dioxide Currently 0.01
• Dominated early atmosphere
• locked up in calcium carbonates (limestone,
  chalks)

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• Carbon cycle
• Accelerated by living sea creatures

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• Does the geologic history of the Earth lead to
  the formation of life?
• Does this make life unique to the Earth?
• Atmosphere has been altered by life
• Existence of extrasolar planets has been
  confirmed

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• Chapter 11 260 278 (Q 1, 2, 3)
• Chapter 8 189 196 (Q 2, 3, 4)