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 Inner core Outer core Mantle Crust Hydrosphere Atmosphere Magnetosphere

Tides 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 Lunar Tides

Figure Solar and Lunar Tides

Tidal locking Moon keeps same face toward earth Revolves and rotates in 27.3 d Synchronous orbit

Figure Tidal Locking

Tidal 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 Earth’s Atmosphere

Earth’s atmosphere Troposphere Stratosphere Mesosphere Ionosphere

Convection Warm air rises Cold air falls Happens in troposphere Winds and weather

Figure 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 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 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 Core Soft asthenosphere Solid rocky lithosphere Crust No hydrosphere, atmosphere, magnetosphere Uniform density Chemically differentiated

Figure 5.11 Global Plates

Plate tectonics 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 Means “seas” (don’t contain water) Roughly circular Dark Flat plains from spread of lava Basaltic 3300 kg/m 3 Mantle material 3.2 to 3.9 billion years old

Figure 5.18 Moon, Close-up

Lunar highlands Several km above maria Lighter colored Rich in aluminum 2900 kg/m 3 More than 4 billion years old

Lunar 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 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 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 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