Transcript Chapter 5: Earth and its Moon - Otto

Chapter 5
Earth and its Moon
The Earth
Table 5-1
Some Properties of Earth and the Moon
Figure 5.1
Earth and Moon
Earth Structure
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Inner core
Outer core
Mantle
Crust
Hydrosphere
Atmosphere
Magnetosphere
Tides
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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 locking
• Moon keeps same face toward earth
• Revolves and rotates in 27.3 d
• Synchronous orbit
Figure 5.4 - Tidal Locking
Tidal bulge drag
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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 atmosphere
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Troposphere
Stratosphere
Mesosphere
Ionosphere
Convection
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Warm air rises
Cold air falls
Happens in troposphere
Winds and weather
Figure 5.6 - Convection
Earth’s temperature
• Absorbs sunlight
• Re-radiates energy
• Average temperature -23°C without
atmosphere
• All water frozen
Greenhouse 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 layer
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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 5-1
Earth’s Growing
Ozone Hole
Discovery 5-2a
The Greenhouse Effect and Global Warming
Discovery 5-2b
The Greenhouse Effect and Global Warming
No 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 interior
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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
Differentiation
• 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 Structure
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Core
Soft asthenosphere
Solid rocky lithosphere
Crust
No hydrosphere, atmosphere,
magnetosphere
• Uniform density
• Chemically differentiated
Figure 5.11
Global Plates
Plate tectonics
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Surface composed of plates
Drift several cm per year
Earthquakes
Continental drift
Mountain building
Ocean ridges
Driven by convection in mantle
Figure 5.12
Himalayas
Figure 5.13
Californian Fault
Figure 5.14
Plate Drift
Figure 5.15
Pangaea
Surface of moon
• No plate tectonics
• No air or water causing erosion
• No ongoing volcanic activity
Figure 5.16
Full Moon, Near Side
Lunar features
• Maria (singular mare)
• Highlands
• Craters
Figure 5.17
Full Moon, Far Side
Lunar maria
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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 highlands
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Several km above maria
Lighter colored
Rich in aluminum
2900 kg/m3
More than 4 billion years old
Lunar cratering
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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 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 erosion
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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 field
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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
Magnetosphere
• 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 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 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
Aurora
• 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 magnetism
• Moon rotates slowly
• No molten or metal rich core
Earth-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 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 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 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 crater
• Some large basins caused by impact
didn’t flood with lava