Nebular Hypothesis

a. Supernova and formation of primordial dust cloud.

NEBULAR HYPOTHESIS

b. Condensation of primordial dust. Forms disk-shaped nubular cloud rotating counterclockwise. c. Proto sun 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 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 sun’s equatorial plane (not randomly organized).

Terrestrial Planets Close to the sun Small rocky.

Jovian Planets Far from the sun Large, gaseous

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.

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 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.

Emissions during degassing. Note that oxygenation of the atmosphere occurs following evolution of plants that use photosynthesis in their life processes.

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.

Metallic meteorites Iron-Nickel

Chondritic meteorites Fe-Mg silicate (rocky)

Evidence of compositional materials: Meteorite composition.

Seismic wave evidence. Compression Waves

Seismic wave evidence: Shear waves.

Seismic waves refract because of velocity changes related to density changes within the earth. Seismic wave accelerate with increasing density.

P-wave shadow zones. Note two shadow zones.

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