Lecture 15: The Earth

"Well, it's a marvelous night for a moondance, With the stars up above in your eyes..."

Van Morrison, Moondance

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    • Date: November 1, 1994
    Reading Assignment: pp. 169-201

    Description : Lunar geology, origin and evolution.

    Objectives

  • understand the bulk properties of the Moon and how they differ from Earth.
  • understand origin of craters and their importance in erosion on the Moon
  • understand origin and evolution of Maria
  • be able to describe why there are more craters in the lunar highlands than in the maria
  • be able to distinguish between the lunar theories of formation and understand why some do not fit the data
  • understand the reasons for space exploration

    • Lecture Outline

    Slide # 1: Lecture 15: The Moon: More than Cheese

  • bulk properties
  • surface features
  • impact craters
  • surface composition
  • volcanos
  • interior
  • origin
  • exploration
    • Slide # 2: EarthÕs Structure
  • core
  • mantle
  • crust
  • hydrosphere
  • atmosphere
  • magnetosphere
    • Slide # 3: Bulk Properties of the Moon
  • radius = 1/4 radius of Earth
  • mass = 1/80 mass of Earth
  • average density = 3.3 gm/cm3
  • rotation = 27.3 days (synchronous)
  • shape = 4 km equatorial bulge
    • Slide # 4: Lunar Atmosphere
  • none
  • primary and secondary atmosphere escaped
  • gravity = 1/6 EarthÕs
    • Slide # 5: Lunar Surface Features
  • craters
  • maria
  • highlands
    • Slide # 6: Craters
  • the main cause of Erosion on the Moon
  • why is it important on the Moon?
  • no atmosphere
  • no other source of erosion
  • no plate tectonics and no new surface
    • Slide # 7: Forming Impact Craters
  • meteoroid strikes the Moon
    • Slide # 8: Forming Impact Craters
  • energy released from impact
    • Slide # 9: Forming Impact Craters
  • Ejecta blanket and seismic waves
    • Slide # 10: A New Crater
  • a fully formed crater
    • Slide # 11: Erosion Rates
  • cratering leads to slow erosion
  • 5 meters per billion years
  • 10,000 time less than on Earth
    • Slide # 12: Dating Lunar Terrain
  • relative ages can be deduced from cratering
  • crater density = # craters per square km
  • high crater density = old surface
    • Slide # 13: Radioactive Dating
  • some elements spontaneous change into other elements
  • the nuclei change
    • Slide # 14: Half-life
  • the time for half of a sample to decay
  • a statement of probability
  • we donÕt know WHICH atoms will change
  • each atom has a 1 in 2 chance to decay in one half-life
  • since most samples contain trillions of atoms, the statistics are very good
    • Slide # 15: Some half-lives
  • U238 = 4.5 Billion Years
  • U235 = 713 Million Years
  • Thorium-232 = 13.9 Billion Years
  • Plutonium-241 = 2.4 Million Years
  • Carbon-14 = 6000 years
    • Slide # 16: Many Half-Lives
  • every half life will decrease the amount of PARENT atoms by 1/2
    • Slide # 17: How do we know the sample started as only Parent Atoms?
  • if the Daughter atoms are gaseous, they would not stay in the rock if it was M
  • radioactive decay measure when the rock was last a liquid
    • Slide # 18: Dating Lunar Terrain
  • radioactive dating of rock samples
  • different areas have different ages
  • maria = 3.2-3.9 billion years old
  • low cratering rate
  • highlands > 4 billion years old
  • high cratering rate
    • Slide # 19: A Sharp Decline in Cratering
  • most cratering ended 3.9 billion years ago
  • some continues today, but at a VERY low rate
    • Slide # 20: Maria
  • appeared to be Oceans when first seen from Earth
  • actually flat areas from early lava flows
  • none seen on the far side of the Moon
    • Slide # 21: Highlands
  • regions which were NOT covered by lava
  • higher than the Maria
  • older surface and more heavily cratered
    • Slide # 22: Surface Composition
  • Highlands
  • 2.9 gm/cm3
  • aluminum
  • light colored low density rocks
  • Maria
  • 3.3 gm/cm3
  • similar to terrestrial Basalt
  • darker, higher density rocks
    • Slide # 23: Basic Rock Types
  • Impact Breccias
  • many small rocks stuck together after impact
  • Regolith
  • lunar dust
  • ejecta blankets
    • Slide # 24: Regolith
  • mostly lunar material (99%)
  • some meteoric dust (1%)
  • 10m to 100m thick
  • NO organic material
  • NO water
    • Slide # 25: Volcanos
  • good evidence that volcanos were once active
  • volcanic craters- lines of craters
  • rille
  • Maria
  • no evidence of ACTIVE volcanism
  • all rocks at least 3 billion years old
    • Slide # 26: Lunar Interior
  • how do we probe the MoonÕs core?
    • Slide # 27: Probing EarthÕs Interior
  • we canÕt directly observe the EarthÕs core
  • we can probe using Seismic Waves
    • Slide # 28: P and S waves
  • S waves cannot travel through liquids
  • P waves can travel through liquids and solids
    • Slide # 29: Earthquakes as Experiments
  • Earthquakes can be detected around the Earth
  • seismic signals pass through the Earth
  • we use these signal to probe the interior
    • Slide # 30: Results of Lunar Seismology
  • Moonquakes occur 1000 km below the surface
  • very thick lithosphere
  • chemically different crust and mantle
  • possible molten core
    • Slide # 31: The MoonÕs Interior
  • average density = 3.3 gm/cm3
  • some seismic evidence of a liquid core?
  • no lunar magnetic field
  • no active volcanos
    • Slide # 32: The Moon
  • cross sectional view
    • Slide # 33: Formation of the Moon
  • Sister Theory
  • Capture Theory
  • Fission Theory
  • Impact Theory
    • Slide # 34: Sister Theory
  • the Moon formed as a separate object orbiting Earth
  • both formed at the same time
    • Slide # 35: Capture Theory
  • the Moon formed as a separate object NOT orbiting Earth
  • the Moon was ÒcapturedÓ by the Earth
    • Slide # 36: Fission Theory
  • the Moon was once PART of Earth
  • Earth breaks apart due to rapid rotation or tidal effects
    • Slide # 37: Impact Theory
  • the young Earth was hit by something big
  • the debris formed the Earth and the Moon
    • Slide # 38: Problems with the Theories
  • Sister Theory
  • composition of Earth and Moon are too different
  • Capture Theory
  • composition of the Earth and Moon are too similar
  • Fission Theory
  • very rapid rotation is unlikely
    • Slide # 39: The Impact Theory
  • probably how the Moon was formed
  • density and composition similar to EarthÕs crust
  • a likely catastrophy
    • Slide # 40: Lunar Exploration
  • the Space Race
    • Slide # 41: What percent of the Federal Budget is NASA?
  • A) 10%
  • B) 5%
  • C) 2%
  • D) 0.5%
    • Slide # 42: Why did we land on the Moon?
  • political reasons
  • technological reasons
  • scientific reasons
    • Slide # 43: Political - the Space Race
  • Soviet vs US Space Technolgy
  • Soviet vs US Military Technology
    • Slide # 44: Technological
  • space exploration creates technology
  • spin-offÕs technologies
    • Slide # 45: Spin-off Technologies
  • materials
  • kevlar, mylar
  • electronics
  • microprocessors, solar cells
  • satellite technology
  • $10-$20 of new business for every $1 spent by NASA
    • Slide # 46: Scientific Benefits
  • density and composition of the Moon
  • better understanding of EarthÕs formation
  • cratering rate vs time
  • better understanding solar system formation
  • better solar observations
    • Slide # 47: Other Benefits to Society
  • Weather Forcasting
  • Earth Resources and Global Change
  • Communications
    • Slide # 48: Intangables
  • our place in the universe
  • goals and achievements
    • Slide # 49: Space after Apollo
  • the Space Shuttle
  • unmanned probes
    • Slide # 50: Our Future?
  • Big Missions
  • The Spacestation
  • Return to the Moon
  • Mars???
  • Vehicles
  • Aerospace Plane
  • Single-stage to Orbit