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NEBULAR
HYPOTHESIS
b. Condensation of primordial
dust. Forms disk-shaped
nubular cloud rotating counter-
clockwise.
a. Supernova and formation of
primordial dust cloud.
c. Proto sun and planets begin to form.
d. Accretion of planetesimals
and differentiation of planets
and moons.
e. Existing solar system takes shape.
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Evidence to support the nebular hypotheses:
1. Planets and moons revolve in a counter-clockwise direction (not random).
2. Almost all planets and moons rotate on their axis in a counter-clockwise direction.
3. Planetary orbits are aligned along the suns equatorial plane (not randomly
organized).
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Terrestrial Planets
Close to the sun
Small rocky.
Jovian PlanetsFar from the sun
Large, gaseous
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Differntiated Earth
1. Iron-Nickel Core
(outer core liquid)
(inner core solid)
2. Fe-Mg Silicate Mantle
3. Fe-Mg-Al Silicate Crust(ocean and continental)
Oceans
Atmosphere
*Compositional zonation
based on density.
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How does the earth become compositionally zoned?
1. Accretion of planetesimals.
2. Initial heating due kinetic energy of colliding
planetesimals and compressional heating.
3. Additional heating from radiocactive decay.
4. Iron catastrophe (melting temperarure of iron
reached and dense iron-nickel sink to core and
lighter materials are displaced outwards (including
silicate rock of mantle and crust, ocean waters andatmospheric gases.
5. Earth become compositionally zoned based on
density (Densest iron-nickel in core-least dense
materials comprise the atmosphere).
6. Convective overturn in asthenosphere, mantle and
outer core still occur today.
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Cratering on the moon is indicative of early accretion process.
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Iron catastrophe and differentiation of the earth. Think about transfer of
heat when the earth is solid versus when it becomes completely moltenfollowing the iron catastrophe.
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Degassing of the earth occurred following iron catastrophe and differentiation. Oceans
and atmosphere form during the differentiation process.
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Emissions during degassing. Note that oxygenation of the atmosphere occursfollowing evolution of plants that use photosynthesis in their life processes.
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Differntiated Earth
1. Iron-Nickel Core
(outer core liquid)
(inner core solid)
2. Fe-Mg Silicate Mantle
3. Fe-Mg-Al Silicate Crust
(ocean and continental)
Oceans
Atmosphere
*Compositional zonation
based on density.
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Evidence of compositional materials: Meteorite composition.
Metallic meteorites
Iron-Nickel
Chondritic meteorites
Fe-Mg silicate (rocky)
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Seismic wave evidence. Compression Waves
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Seismic wave evidence: Shear waves.
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Seismic waves refract because of velocity
changes related to density changes within theearth. Seismic wave accelerate with increasing
density.
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P-wave shadow zones. Note two shadow zones.
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S-wave shadow zone. Note S-waves absorbed by the liquid outer core.
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