NEBULAR HYPOTHESIS

b. Condensation of primordial dust. Forms disk-shaped nebular cloud rotating counter-clockwise.

a. Supernova and formation of primordial dust cloud.

c. Protosun and planets begin to form.

d. Accretion of planetesimals and differentiation of planets and moons.

e. Existing solar system takes shape.

Evidence to support the nebular hypothesis:

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 sun’s equatorial plane (not randomly organized).

Terrestrial Planets

Close to the sun

Small rocky.

Jovian Planets

Far from the sun

Large, gaseous

Differentiated 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)

4. Oceans5. Atmosphere

*Compositional zonation

based on density.

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 radioactive decay.

4. Iron catastrophe (melting temperature 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 and atmospheric 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.

Cratering on the moon is indicative of early accretion process.

Iron catastrophe and differentiation of the earth. Think about transfer of heat when the earth is solid versus when it becomes completely molten following the iron catastrophe.

Degassing of the earth occurred following “iron catastrophe” and differentiation. Oceans and atmosphere form during the differentiation process.

Evidence of compositional materials: Meteorite composition.

Metallic meteorites

Iron-Nickel

Chondritic meteorites

Fe-Mg silicate (rocky)

Seismic wave evidence. Compression Waves

Seismic wave evidence: Shear waves.

P-wave shadow zones. Note two shadow zones.

S-wave shadow zone. Note S-waves absorbed by the liquid outer core.