chapter 5 earth and its moon. the earth table 5-1 some properties of earth and the moon
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Chapter 5Earth and its Moon
Chapter 5Earth and its Moon
The Earth
Table 5-1Some Properties of Earth and the Moon
Figure 5.1 Earth and Moon
Earth StructureEarth Structure
• Inner core
• Outer core
• Mantle
• Crust
• Hydrosphere
• Atmosphere
• Magnetosphere
TidesTides
• Variation in ocean level
• Two high tides daily
• Two low tides daily
• Vary from several cm to several m
• Tidal force is differential force
Figure 5.2 - Lunar Tides
Figure 5.3 - Solar and Lunar Tides
Tidal lockingTidal locking
• Moon keeps same face toward earth
• Revolves and rotates in 27.3 d
• Synchronous orbit
Figure 5.4 - Tidal Locking
Tidal bulge dragTidal bulge drag
• Slows rotation of earth
• Day was 21 hours 500 million years ago
• Year was 410 days long
• Eventually moon’s revolution will be synchronized with earth’s rotation
Figure 5.5 - Earth’s Atmosphere
Earth’s atmosphereEarth’s atmosphere
• Troposphere
• Stratosphere
• Mesosphere
• Ionosphere
ConvectionConvection
• Warm air rises
• Cold air falls
• Happens in troposphere
• Winds and weather
Figure 5.6 - Convection
Earth’s temperatureEarth’s temperature
• Absorbs sunlight
• Re-radiates energy
• Average temperature -23°C without atmosphere
• All water frozen
Greenhouse effectGreenhouse effect
• Carbon dioxide and water vapor trap radiated infrared radiation
• Raises average temperature 40 K
• Above freezing point of water
Figure 5.7 Greenhouse
Effect
Ozone layerOzone layer
• Straddles stratosphere and mesosphere
• Ozone is 3 oxygen atoms per molecule
• Protects life from damaging UV
• Man-made chlorofluorocarbons (CFCs)
• CFCs release chlorine
• Chlorine attacks Ozone
Discovery 5-1Earth’s Growing
Ozone Hole
Discovery 5-2aThe Greenhouse Effect and Global Warming
Discovery 5-2bThe Greenhouse Effect and Global Warming
No lunar atmosphereNo lunar atmosphere
• Moon’s gravity too weak to hold atmosphere
• No atmosphere to moderate temperature
• 100 K to 400 K fluctuations
• Some water ice at lunar poles
Earth’s interiorEarth’s interior
• Seismic (earthquake) waves
• P-waves and S-waves
• Outer core liquid (thick)
• Inner core solid
• Core is iron and nickel
Figure 5.8 P- and S-waves
Figure 5.9 Seismic Waves
DifferentiationDifferentiation
• Variation in composition and density between mantle and core
• Earth was molten in past
• Early bombardment
• Nuclear radioactivity
Figure 5.10 Earth’s Interior
Moon StructureMoon Structure
• Core• Soft asthenosphere• Solid rocky lithosphere• Crust• No hydrosphere, atmosphere,
magnetosphere• Uniform density• Chemically differentiated
Figure 5.11 Global Plates
Plate tectonicsPlate tectonics
• Surface composed of plates
• Drift several cm per year
• Earthquakes
• Continental drift
• Mountain building
• Ocean ridges
• Driven by convection in mantle
Figure 5.12Himalayas
Figure 5.13Californian Fault
Figure 5.14 Plate Drift
Figure 5.15 Pangaea
Surface of moonSurface of moon
• No plate tectonics
• No air or water causing erosion
• No ongoing volcanic activity
Figure 5.16Full Moon, Near Side
Lunar featuresLunar features
• Maria (singular mare)
• Highlands
• Craters
Figure 5.17 Full Moon, Far Side
Lunar mariaLunar maria
• Means “seas” (don’t contain water)• Roughly circular• Dark• Flat plains from spread of lava• Basaltic• 3300 kg/m3
• Mantle material• 3.2 to 3.9 billion years old
Figure 5.18 Moon, Close-up
Lunar highlandsLunar highlands
• Several km above maria
• Lighter colored
• Rich in aluminum
• 2900 kg/m3
• More than 4 billion years old
Lunar crateringLunar cratering
• Formed long ago by meteoritic impact
• Fast moving object (several km/s)
• Tremendous impact energy
• Pushes flat material up and out
• Forms crater
• Ejecta blanket
Figure 5.19 Meteoroid Impact
Cratering rateCratering rate
• Older highlands have more craters
• Younger maria have less craters
• Meteoritic bombardment rate dropped 3.9 billion years ago
• End of accretion process in which planetesimals became planets
• Roughly constant rate since then
Figure 5.20 Lunar Craters
Figure 5.21 Lunar Surface
Lunar erosionLunar erosion
• 10 km crater every 10 million years
• 1 m crater per month
• 1 cm crater every several minutes
• Accumulated dust from impacts (lunar regolith) averages 20 m deep
• Deepest on highlands
• Shallowest on maria
Earth’s magnetic fieldEarth’s magnetic field
• Earth acts as if it contains a giant magnet• Creates magnetic field in and around earth• Compasses respond to this magnetic field• North and south magnetic poles roughly
aligned with the earth’s rotation axis• Magnetic N is 13.5° E of true N in LB• Caused by charged particles in earth’s molten
metallic core
MagnetosphereMagnetosphere
• Region in space around a planet influenced by planet’s magnetic field
• Buffer zone between planet and high energy particles of solar wind
Figure 5.22 Earth’s Magnetosphere
Magnetism and particlesMagnetism and particles
• Magnetism does not affect neutral particles and electromagnetic radiation
• Charged particles can be trapped by magnetic field
• Electrons and protons spiral around field lines
Van Allen beltsVan Allen belts
• Discovered in the 1950’s
• Charged particles in solar wind trapped in doughnut shaped regions
• Inner belt mostly protons, 3000 km above earth’s surface
• Outer belt mostly electrons, 20,000 km above earth’s surface
Figure 5.23 Van Allen Belts
AuroraAurora
• Some charged particles escape from Van Allen belts above north and south poles
• Collide with air molecules and create light show
• Aurora borealis or Northern Lights
• Aurora australis or Southern Lights
Figure 5.24 Aurora Borealis
No lunar magnetismNo lunar magnetism
• Moon rotates slowly
• No molten or metal rich core
Earth-moon formationEarth-moon formation
• Earth formed about 4.6 billion years ago
• Moon probably formed by a collision of Mars sized object with earth
• Iron core left behind, moon made of mantle type material
Figure 5.25 Moon Formation
Earth evolutionEarth evolution
• During molten phase, earth became differentiated in density and chemistry
• Intense meteoritic bombardment ended 3.9 billion years ago
• Surface cooled first, developing crust
• Core is still partially molten
Lunar evolutionLunar evolution
• Oldest rocks in lunar highlands 4.4 billion years old
• Early meteoritic bombardment kept surface layers molten
• Moon cooled more quickly than earth• After bombardment, lunar crust and basins
remained• 3.9 to 3.2 billion years ago basins flooded
with basaltic flow - these became maria
Figure 5.26 Lunar Evolution
Far side of moonFar side of moon
• Earth’s gravity formed thicker lunar crust on far side of moon than on near side
• Near side had substantial volcanic activity
• Far side had little substantial activity
Figure 5.27 Large Lunar Crater
Large impact craterLarge impact crater
• Some large basins caused by impact didn’t flood with lava