Quest 2 Review

Earth Physical Strat

• Lithosphere (Brittle)  

o Crust, Upper Mantle 

• Athenosphere (ductile) 

• Mantle (Solid, but convecting) 

• Outer Core (liquid) 

• Inner Core (Core) 

• Exosphere

• Thermosphere

• Mesosphere

• Stratosphere

• Troposphere

Earth Compositional Strat

• Crust (Silicate rock) 

o Oceanic - mafic 

o Continental - felsic  

• Mantle (Silicate rock) 

o Ultramafic  

• Core (metal) 

o Fe - 96%  

o Ni - some nickel something else (O, S) 

Moon

• Diameter ~1/4Earth’s

• Mass ~ 1% Earth’s

• Orbits ~ 30Earth Diameters

• Mean Surface Temperature

• No global Magnetic Field

• Not Atmosphere

Impact Craters 

From Asteroids and Comets

Highlands

• Older and Brighter 

• Lots of craters

• Mountains (rupes)

• Magma ocean 

  • Supported physically- heavy silicate minerals sink, light minerals float

  • Supported compositionally - europium anomaly, substituted for CA

• Mare (Maria)

• Younger and Darker

• Fewer crater

• Maria has fewer craters than the lunar highlands, so it is not so exposed to impacts. 

• Suggests that impacts are related

Regolith

• Impact debris 

• House-size boulders down to dust 

• Footprints left in regolith (very fine)

Capture Theory

random flew too close and got trapped by gravitational dynamics ( not good, the moon is too similar to Earth for it to be random and get trapped) 

Fission Theory 

Earth spins so fast that it spins off a blob to be a moon (composition it could be, volatile don't match, dynamically it doesn't match)

Giant Impact

Nearly fully formed proto-earth hit by a Mars-sized impactor (Thea), iron core of Thea merges with earth, rocky mantle of earth and Thea form the moon ~40- 60million years into SS

Best theory because very consistent throughout the solar system, satisfies dynamical observation, and provides heat for the magma ocean.

New Moon

moon and sun are on the same side of Earth (Conjunction). Best time to observe objects in the night sky 

 Full Moon

moon and sun are on opposite sides of Earth, rise at sunset, set at sunrise, highest at midnight

First Quarter Moon

moon and sun are 90 degrees apart (after new moon), rise at noon, set at midnight, highest at  sunset

Gibbous and crescent moon

between the 1st and 3rd quarter phases

Third Quarter Moon

Moon and sun are 90 apart (after full moon), highest at sunrise • Waxing (increasing) - after New Moon and before Full Moon, more illuminated side

Waning (decreasing)

after full moon and before New Moon, less illuminated side

Restoring force

 force acting to bring a body to its equilibrium, acts until synchronous rotation is achieved

Off-axis

tidal bulge allows for transfer of momentum from Earth's rotation to the Moon's orbital motion, confirming that the Moon is spiraling away from Earth about 4 cm per year

Umra

 Full Shadow region, the entire sun is blocked 

Penumra

 Partial shadow region, part of the sun is blocked

Lunar Eclipse

Moon is in Earth’s shadow 

• Occurs when Earth shades the moon, only during a full moon, total (moon entirely within umra), partial (moon particular within umra)

Solar Eclipse

Earth is in the Moon’s shadow 

• Occurs when the moon passes in front of the sun, only during a new moon, total (Earth passes through the umbra), Partial (Earth passes through the penumbra), Annular (Earth passes beyond the umbra)

Reddening of the moon

caused by sunlight refracting through the Earth’s atmosphere

Catastrophism

the theory that the earth has largely been shaped by sudden, short-lived, violent events, possibly worldwide in catastrophe

Uniformitarianism

 holds that slow, incremental changes, such as tectonic uplift and erosion, created all the Earth’s geological features.

Impactor

(bolide) - Mass, Velocity

Target Body

• Size (mass) ‘gravity well”

• Compositional 

• Atmosphere

Total Mechanical Energy

• Kinetic Energy = Potential Energy

  • Kinetic Energy: ½ Mass Velocity^2

Impact Crater

Release of large amounts of energy

Initial Explosion

• lots of energy is used to break, melt, vaporize materials,

  • Very fast (a few seconds to a few minutes)

  • Very high temperature 

Crater Excavation

•  initial “hole” collapse and forms the final crater we see

  • Collapse: relatively fast (a few seconds to minutes)

  • Crater degradation: very long (millions of years)

Simple Crater

• Energy Release vs. gravity vs. cohesion

• Slopes are much steeper 

• Depth-to-width ratios and melt components are quite different 

Complex Crater

• Internal structures present ( peaks and rings)

• Geologic Evidence of Impact 

• breccia and mega breccia 

• Pseudotachylite 

• Shatter cones and shocked materials 

• Melt sheets

• Tektites

• K/T Geologic boundary

• K/T Geologic boundary

• End-Cretaceous extinction

• 1st major stratigraphic boundary identified

• Iridium anomaly discovered 

  • Earth’s crust is depleted in Ir & asteroids are enriched in Ir

• Heat pulse and global fires 

Saturation

•  Densities reach maximum when each new crater destroys one old crater 

• Equilibrium 

• New crater wipes out an equal number of old ones

Production population

 theorized size-frequency distribution of all primary

Geometric saturation

hexagonal close packing

Lunar crater densities

can be compared with measured surface ages from samples.

Crater size-frequency plots

 can be used to infer the geological history of the surfaces

geological processes(erosion, sedimentation)

will remove smaller craters more rapidly than larger ones, so the surface tends to look younger at small scales rather than at large scales

Secondary craters

can seriously complicate the cratering record; the surface may be buried and then exhumed, giving misleading dates

Obliquity

 Tilt of a planet's spin axis relative to the plane of its orbit around the sun,  Causes seasons - March 21 (Spring equinox), Dec 21 (Winter Solstice), June 21 (Summer  Solstice), Sept 23 (Fall Equinox) , 23.4°

 Lunar Orbital Inclination

 5.14°

Lunar Obliquity to ecliptic

 1.54°

Lunar Obliquity

6.68°

As the moon orbits Earth

different fractions of the illuminated side show day and night

Day and Month on Earth

The moon is 1:1 synchronous rotation/revolution, meaning it spins once it makes  one revolution around the Earth 

Day and Night on the moon

 daylight for 2 weeks, and then nights for about 2 weeks

Sidereal Month

One orbit around Earth with respect to stars, 27.3 days

Synodic Month

One orbits around Earth with respect to the sun in 29.5 days

 energies associated with planetary heat engines

• Accretion, Differentiation, Radioactive Decay

 energies associated with planetary cooling mechanisms.  

• Conduction, convection, advection, radiation

Simple vs Complex Crater

depend on the composition of both the target and the impact, location closeness to the sun, the fewer components of the body, the less it's gonna decrease