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