______________________________

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

a. Supernova and formation of primordial ______________.

c. Proto sun and ____________ begin to form.

d. Accretion of planetesimals and differentiation of planets and ________ (~________ billion years ago).

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 _________________________________ direction.

3. Planetary orbits are aligned along the _________________________________

_____________: More Evidence from the Early Solar System

• ________________________are composed of undifferentiated, primordial matter that has remained nearly unchanged for about 4.6 billion years. These stony meteorites formed nearly simultaneously with the Sun.

• It is thought that small droplets of magma crystallized into the minerals rich in ________________________from the hot solar nebula. These spheres are called ______________.

Thin Section View

_____________: More Evidence from the Early Solar System

• Most of Earth’s early history has been wiped out by _______________________.

• The moon has remained virtually unchanged for the past _____________years.

• The Moon’s cratered surface shows many craters, evidence of _______________________.

• Earth was probably bombarded even more than the Moon early in its history. Why?

Number of Large Impacts

Gyr = gigayear = billion years

Terrestrial Planets:

•____________: inside the “frost line.”

•_____________________________________________________________________

Jovian PlanetsFar from the sun, low density

Large, gaseous (hydrogen, methane)

________ Planets

•Far from the sun

•Large, gaseous

How did the earth become compositionally zoned?

1. _____________________________

2. Heating due ___________of colliding planetesimals and ______________________.

3. Heating from decay of ___________________.

4. Iron catastrophe : ___________melt, and these heavy elements sink to core. Lighter materials are displaced outwards: silicate rock of mantle and crust, ocean waters and atmospheric gases, etc.

5. Earth become compositionally zoned based on __________ (Densest iron-nickel in core-least dense materials comprise the atmosphere).

6. Convective overturn in asthenosphere, mantle and outer core still occur today.

7. Most of the heat generated is still trapped—rock is a good insulator..

Iron ________________ and differentiation of Earth. As iron “falls” towards center and stops, its kinetic transfers into the production of more heat, leading to a runaway process (_____________ feedback loop).

Emissions from degassing of the Earth during its differentiation.

Note that molecular _____________escape to space and that oxygenation of the atmosphere occurred later following evolution of marine algae and plants that use photosynthesis to convert CO2 to O2 as a part of their life processes.

Degassing occurred following the iron catastrophe and differentiation. Oceans and atmosphere formed during this period, though __________________ continue to escape today.

Formation of Moon• After the formation of Earth’s core, it

is believed an __________________ approximately the size of _____________collided with Earth.

• The collision re-melted Earth’s outer layers, and debris from the collision spun off into orbit

• The two mostly molten bodies reformed spherical shapes

• Evidence: Moon’s composition is similar to Earth’s mantle; isotopic dating of Moon rocks.

• The moon cooled quicklydue to its small size and has remained largely unchanged, except for _____________________________

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. Oceans

5. Atmosphere

How is the earth compositionally zoned?

denser

lighter

______________________________

Differentiated Earth1. Iron Core

(solid inner core)

(liquid outer core)

2. Fe-Mg Silicate Mantle

3. Silicate Crust

(oceanic and continental)

4. Oceans

5. Atmosphere

.

Evidence of Earth’s Composition and Structure?

• _________: down to ~3.6 km• __________: down to ~15 km• _____________~ (most

geochemists think hot spot volcanoes such as Hawaii tap the deep mantle~2700 km, based on experimental evidence.)

• Center of Earth: down to ~6400 km. Evidence?

How do we know about the composition of the core and lower mantle?

Indirect Evidence:•Seismic waves

Seismology• Fluids (liquids and gases) support only

one type of sound wave: compressional (______________________________).

• Solids ALSO support a second type: shear (_____________). Both types start together but travel at different speeds-- shear waves are always slower.

Seismic wave evidence. ____________ Waves (P-waves): Velocity: 6-7 km/sec within lithosphere. Propagate through_____phases of matter.

Seismic wave evidence: _________ waves (S waves): velocity 3-4 km/sec. Only propagate through _______ phases of matter.

Seismic waves _______ (bend) because of velocity changes related to density changes within the earth. Seismic wave speed up with increasing ____________.

Note the change in seismic wave velocity as the seismic waves propagate through the earth.

Note the decrease in seismic wave velocity at a depth of 100-350 km and at the mantle-core boundary.

Note that S-waves are only absorbed at the mantle-core boundary. What does that tell you about the physical property of the upper mantle? Answer:

• P-wave shadow zones. Note two shadow zones exist between 105°-140° from the epicenter due refraction at outer core mantle boundary.

• S-wave shadow zone. Note only one large shadow zones at an angle greater than 105° of the epicenter, due refraction at outer core mantle boundary and because S-waves are absorbed by the liquid outer core.

How do we know what the composition of the core and lower mantle is?

_____________________•The location of Magnetic North changes over time as convection currents shift and sometimes reverse

The presence of the Earth’s magnetic field provides evidence that the Earth likely possesses a _____________ core and that a component of this core must be liquid _________ and convecting around the solid metallic portion of the core.

How do we know what the composition of the core and lower mantle is?

______________________________•About 5% of meteorite finds are metallic meteorites •Meteorite composition: mostly Fe with ~6-17% _____; and small amounts of other metals•Widmanstatten Pattern: formed from slow cooling of metals—can only happen in cores of larger bodies

Metallic Meteorites•________________________: olivine crystals in a metallic matrix. Believed to have been formed at the core-mantle boundary of a planetoid large enough to form a core.

•______________________: origin unknown—probably from a parent body that was too small to form a metallic core. Also composed of Fe-Ni chondrules together with silicate (rocky) chondrules.

Pallasite

CB Chondrite

How do we know what the composition of the core and lower mantle is?

Evidence of Earth’s core: since other planet-like bodies in our Solar System formed Fe-Ni cores and rocky mantles, and since Ni is a fairly common element, it is believed that Earth’s core is composed of Fe and Ni, as well as smaller amounts of other elements.

Metallic meteorites

Iron-Nickel

Chondritic meteorites

Fe-Mg silicate (rocky)

Earth’s Internal Structure

• _______2-70 km thick. Oceanic crust is thinner (8-10km) and denser than continental crust (35 km on average).

• _______2900 km thick. 80% of Earth’s volume but only 67% of its mass. Solid.

• _______Outer core 2200 km thick, liquid iron. Inner core radius 1200 km, solid iron.

Compositional Boundaries:

Earth’s Internal Structure

• Lithosphere: Lithos = rock. Lithosphere is brittle (can produce earthquakes)

• Asthenosphere: asthenos = soft. Asthenosphere is ductile (bends instead of breaking).

_________________ Boundaries:

Lithosphere “floats” on a partially melted asthenosphere, similar to a raft floating on water. The lithosphere is in isostatic equilibriium with the asthenosphere.

Crust vs. Mantle is a compositional boundary. Both are made of silicates (oxygen, silicon, various metals), but the bulk chemistry is different.

Lithosphere vs. Asthenosphere is a behavioral boundary. Lithos = rock, asthenos = soft. Lithosphere is brittle (can produce earthquakes) and asthenosphere is ductile (bends instead of breaking).

Tectonic plates are LITHOSPHERE.

Earth’s Internal Structure

P-wave velocity profile within the lithosphere (continental and ocean crust and uppermost solid mantle) and asthenosphere (upper ductile mantle).

Low velocity zone (100-350 km) in the upper mantle is due to decreasing density. This low velocity zone defines the asthenosphere.

Why does the density decrease in this region of the upper mantle?

It is partially molten

Internal Convection• Convection in the liquid

outer core produces the magnetic field.

• Convection in the asthenosphere moves the tectonic plates (pieces of lithosphere) around on the surface and is responsible for most geologic activity, such as volcanoes, earthquakes, etc.

“Typical” picture of convection currents and plate tectonics

Plate Boundaries_______________: Plates move apart, new ______________ crust is formed in between.

Convergent: Plates move together and either collide (continental-continental) or one is __________________ (oceanic-continental or oceanic-oceanic). Continents stay on ___________.

Transform: Plates _________ past each other.