discovering the universe earth and moon

8/9/2019 Discovering the Universe Earth and Moon

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Discovering the UniverseDiscovering the Universe

Eighth EditionEighth Edition

Discovering the UniverseDiscovering the Universe

Eighth EditionEighth Edition

Neil F. Comins William J. Kaufmann III

Earth and MoonEarth and MoonEarth and MoonEarth and Moon


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WHAT DO YOU THINK?

1.1. How old is the EarthHow old is the Earth? How do we know??? How do we know??

2.2. Can EarthsCan Earths ozoneozone layer, which is now being depleted,layer, which is now being depleted,

be replenished?be replenished?

3.3. What is theWhat is the greenhouse effectgreenhouse effect? Is? Is Global WarmingGlobal Warmingreal?real?

4.4. What causes theWhat causes the ocean tidesocean tides??

5.5. Do we see all parts of the Moons surface at some timeDo we see all parts of the Moons surface at some time

throughout the lunar cycle?throughout the lunar cycle?6.6. How did the moon formHow did the moon form? How do we know?? How do we know?


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When did the planets form?When did the planets form?

We cannot find the age of a planet, butWe cannot find the age of a planet, but

we can find the ages of the rocks thatwe can find the ages of the rocks that

make it up.make it up. We can determine the age of a rockWe can determine the age of a rock

through careful analysis of thethrough careful analysis of the

proportions of various atoms andproportions of various atoms andisotopes within it.isotopes within it.


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Radioactive DecayRadioactive Decay

SomeSome

isotopesisotopes

decay intodecay intoother nuclei.other nuclei.

AAhalfhalf--lifelife isis

the time forthe time for

half thehalf thenuclei in anuclei in a

substance tosubstance to

decay.

decay.


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Thought QuestionThought Question

Suppose you find a rock originally made ofSuppose you find a rock originally made ofpotassiumpotassium--40, half of which decays into argon40, half of which decays into argon--4040every 1.25 billion years. You open the rock andevery 1.25 billion years. You open the rock and

find 15 atoms of argonfind 15 atoms of argon--40 for every atom of40 for every atom ofpotassiumpotassium--40.How long ago did the rock form?40.How long ago did the rock form?

A.A. 1.25 billion years ago1.25 billion years ago

B.B. 2.5 billion years ago2.5 billion years agoC.C. 3.75 billion years ago3.75 billion years ago

D.D. 5 billion years ago5 billion years ago


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Suppose you find a rock originally made ofSuppose you find a rock originally made ofpotassiumpotassium--40, half of which decays into argon40, half of which decays into argon--4040every 1.25 billion years. You open the rock andevery 1.25 billion years. You open the rock andfind 15 atoms of argonfind 15 atoms of argon--40 for every atom of40 for every atom ofpotassiumpotassium--40.How long ago did the rock form?40.How long ago did the rock form?

A.A. 1.25 billion years ago1.25 billion years ago

B.B. 2.5 billion years ago2.5 billion years ago

C.C. 3.75 billion years ago3.75 billion years agoD.D. 5 billion years ago5 billion years ago


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Age dating ofAge dating ofmeteorites that aremeteorites that areunchanged since theyunchanged since theycondensed andcondensed andaccreted tells us thataccreted tells us thatthe solar system isthe solar system isabout 4.6 billion yearsabout 4.6 billion yearsold.old.

Dating the Solar System


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Dating the Solar SystemDating the Solar System

Radiometric dating tells us that the oldestRadiometric dating tells us that the oldestmoon rocks are 4.4 billion years old.moon rocks are 4.4 billion years old.

The oldest meteorites are 4.55 billionThe oldest meteorites are 4.55 billionyears old.years old.

Planets probably formed 4.5 billion yearsPlanets probably formed 4.5 billion yearsago.ago.

But Earths crust rocks date to 3 or4But Earths crust rocks date to 3 or4billion years only why?billion years only why?


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Professor, didnt YOU say everyProfessor, didnt YOU say every

measurement in science is uncertain???measurement in science is uncertain???

Couldnt YOU be wrong?Couldnt YOU be wrong? The Earth is the center of the universe.The Earth is the center of the universe.

The Earth is flat.The Earth is flat.

The continents are fixed upon Earth.The continents are fixed upon Earth.

Chernobyl and ThreeChernobyl and Three--MileMile--Island are safeIsland are safe

Intelligence is determined by race.Intelligence is determined by race.

Dating the EarthDating the Earth


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Good scienceGood science

Seeks natural laws to explain similarSeeks natural laws to explain similar

phenomenaphenomena

Adapts to new dataAdapts to new data

Looks for patterns and corroborationLooks for patterns and corroboration

Requires independent lines of evidenceRequires independent lines of evidence

Depends upon experiment, not personalDepends upon experiment, not personalvaluesvalues

Dating the EarthDating the Earth


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The Origin of the Moon: AnThe Origin of the Moon: An

Example of the Process of ScienceExample of the Process of Science

Where did theWhere did the

moon comemoon comefrom?from?

How do weHow do we

know?know?


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How do we explain theHow do we explain the

existence of our Moon?existence of our Moon?

Terrestrial planets dont have moons.

Our Moon is VER

Y large compared to its partnerComposition is both like Earth

Rocky materials, similar to Earths Crust

and NOT like Earth:

No water, no atmosphere, not a large metal core


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FOUR (4)Theories

Formed at the same time, alongside Earth Formed from Earths materials

Captured as it passed by

Result of Giant Impact


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Formed at the same time, alongside Earth

The Sister TheoryBut then

Should have the same composition

Should have water & volatiles

Should have similar density

It doesnt, so rule this one out


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Formed from Earths materials

As earth formed, it spun outFission Theory

But then. again

Should have water & volatiles

Should have similar density

It doesnt, so rule this one out


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Captured as it passed by

Capture TheoryBut then.

How can this be done?

It is very unlikely, so rule this one out


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Captured MoonsCaptured Moons

The unusual moons of some planetsThe unusual moons of some planetsmay be captured planetesimals.may be captured planetesimals.


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Result ofGiant Impact

Mars-sized impactor strikes Earth a glancing blow Impactor destroyed, creates a debris ring

Gravity takes over.the Moon is born.

Lacks volatiles and water & Iron

Computer models show this to be possible!


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Giant ImpactGiant Impact

Giant impact stripped matter from Earths crustGiant impact stripped matter from Earths crust

Stripped matter began to orbitStripped matter began to orbit

Then accreted into MoonThen accreted into Moon


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Earth as a PlanetEarth as a Planet

Our goals for learning:Our goals for learning:

Why is Earth geologically active?Why is Earth geologically active? What processes shape Earths surface?What processes shape Earths surface?

How does Earths atmosphere affect theHow does Earths atmosphere affect the

planet?planet?


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Why is Earth geologicallyWhy is Earth geologically

active?active?


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Earths InteriorEarths Interior

CoreCore:: HighestHighestdensity; nickeldensity; nickeland ironand iron

MantleMantle::ModerateModeratedensity; silicon,density; silicon,oxygen, etc.oxygen, etc.

CrustCrust:: LowestLowestdensity; granite,density; granite,basalt, etc.basalt, etc.


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Terrestrial Planet InteriorsTerrestrial Planet Interiors

Applying what we have learned about EarthsApplying what we have learned about Earthsinterior to other planets tells us what theirinterior to other planets tells us what theirinteriors are probably like.interiors are probably like.


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Why do water and oil separate?Why do water and oil separate?

A.A. Water molecules repel oil moleculesWater molecules repel oil moleculeselectrically.electrically.

B.B. Water is denser than oil, so oil floatsWater is denser than oil, so oil floatson water.on water.

C.C. Oil is more slippery than water, so itOil is more slippery than water, so it

slides to the surface of the water.slides to the surface of the water.D.D. Oil molecules are bigger than theOil molecules are bigger than the

spaces between water molecules.spaces between water molecules.


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Why do water and oil separate?Why do water and oil separate?

A.A. Water molecules repel oil moleculesWater molecules repel oil moleculeselectrically.electrically.

B.B. Water is denser than oil, so oilWater is denser than oil, so oilfloats on water.floats on water.

C.C. Oil is more slippery than water, so itOil is more slippery than water, so it

slides to the surface of the water.slides to the surface of the water.D.D. Oil molecules are bigger than theOil molecules are bigger than the

spaces between water molecules.spaces between water molecules.


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DifferentiationDifferentiation

Gravity pullsGravity pullshighhigh--densitydensitymaterial tomaterial to

centercenter LowerLower--densitydensity

material rises tomaterial rises tosurfacesurface

Material ends upMaterial ends upseparated byseparated bydensitydensity


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What is necessary forWhat is necessary fordifferentiationdifferentiation to occur in ato occur in aplanet?planet?

A.A. It must have metal andIt must have metal and rock in it.rock in it.B.B. It must be a mix of materials of different density.It must be a mix of materials of different density.

C.C. Material inside must be able to flow.Material inside must be able to flow.

D.D. All of the above.All of the above.

E.E. b and c.b and c.


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What is necessary forWhat is necessary fordifferentiationdifferentiation to occur in ato occur in aplanet?planet?

A.A. It must have metal andIt must have metal and rock in it.rock in it.B.B. It must be a mix of materials of different density.It must be a mix of materials of different density.

C.C. Material inside must be able to flow.Material inside must be able to flow.

D.D. All of the above.All of the above.

E.E. b and c.b and c.


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LithosphereLithosphere

A planets outerA planets outerlayer of cool,layer of cool,rigid rock isrigid rock is

called thecalled thelithosphere.lithosphere.

It floats on theIt floats on thewarmer, softerwarmer, softer

rock that liesrock that liesbeneath.beneath.


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Do rocks sDo rocks s--tt--rr--ee--tt--cc--h?h?

A.A. NoNorock is rigid and cannot deformrock is rigid and cannot deformwithout breaking.without breaking.

B.B. YesYesbut only if it is molten rock.but only if it is molten rock.

C.C. YesYesrock under strain may slowlyrock under strain may slowlydeform.deform.


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Do rocks sDo rocks s--tt--rr--ee--tt--cc--h?h?

A.A. NoNorock is rigid and cannot deformrock is rigid and cannot deformwithout breaking.without breaking.

B.B. YesYesbut only if it is molten rock.but only if it is molten rock.

C.C. YesYesrock under strain may slowlyrock under strain may slowlydeform.deform.


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Strength ofRockStrength ofRock

Rock stretches whenRock stretches whenpulled slowly butpulled slowly butbreaks when pulledbreaks when pulled

rapidly.rapidly. The gravity of a largeThe gravity of a large

world pulls slowly onworld pulls slowly onits rocky content,its rocky content,

shaping the world intoshaping the world intoa sphere.a sphere.


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Sources ofInternal HeatSources ofInternal Heat

1.1. GravitationalGravitational

potential energypotential energyof accretingof accreting

planetesimalsplanetesimals

2.2. DifferentiationDifferentiation

3.3. RadioactivityRadioactivity


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Heating ofInterior overTimeHeating ofInterior overTime

Accretion andAccretion anddifferentiationdifferentiationwhen planetswhen planets

were youngwere young

RadioactiveRadioactivedecay is mostdecay is mostimportant heatimportant heatsource todaysource today


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Cooling ofInteriorCooling ofInterior

ConvectionConvectiontransports heattransports heatas hot materialas hot material

rises and coolrises and coolmaterial fallsmaterial falls

ConductionConductiontransfers heattransfers heatfrom hotfrom hot

material to coolmaterial to coolmaterialmaterial

RadiationRadiationsends energysends energy

into spaceinto space


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What cools off faster?What cools off faster?

A.A. A grandeA grande--size cup of Starbucks coffeesize cup of Starbucks coffee

B.B. A teaspoon of cappuccino in the sameA teaspoon of cappuccino in the samecupcup


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A.A. A grandeA grande--size cup of Starbucks coffeesize cup of Starbucks coffee

B.B. A teaspoon of cappuccino in the sameA teaspoon of cappuccino in the samecupcup


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A.A. A big terrestrial planetA big terrestrial planet

B.B. A tiny terrestrial planetA tiny terrestrial planet


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A.A. A big terrestrial planetA big terrestrial planet

B.B. A tiny terrestrial planetA tiny terrestrial planet


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Role of SizeRole of Size

Smaller worlds cool off faster and hardenSmaller worlds cool off faster and hardenearlier.earlier.

Moon and Mercury are now geologically dead.Moon and Mercury are now geologically dead.


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Surface Area to Volume RatioSurface Area to Volume Ratio

Heat content depends on volume.Heat content depends on volume.

Loss of heat through radiation depends onLoss of heat through radiation depends onsurface area.surface area.

Time to cool depends on surface area dividedTime to cool depends on surface area dividedby volume:by volume:

surface area to volume ratio =4Tr2

4

3Tr

3

!

3

r

Larger objects have a smaller ratio and coolLarger objects have a smaller ratio and coolmore slowly.more slowly.


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Planetary Magnetic FieldsPlanetary Magnetic Fields

Moving charged particles create magneticMoving charged particles create magnetic

fields.fields.

A planets interior can create magnetic fields ifA planets interior can create magnetic fields if

its core is electrically conducting, convecting,its core is electrically conducting, convecting,

and rotating.and rotating.


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Earths MagnetosphereEarths Magnetosphere

Earths magnetic fields protects us fromEarths magnetic fields protects us fromcharged particles from the Sun.charged particles from the Sun.

The charged particles can create auroraeThe charged particles can create aurorae

(Northern lights).(Northern lights).


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If the planet core is cold, do you expect it toIf the planet core is cold, do you expect it tohave magnetic fields?have magnetic fields?

A.A. Yes, refrigerator magnets are cold, andYes, refrigerator magnets are cold, andthey have magnetic fields.they have magnetic fields.

B.B. No, planetary magnetic fields areNo, planetary magnetic fields are

generated by moving charges around,generated by moving charges around,and if the core is cold, nothing is moving.and if the core is cold, nothing is moving.


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If the planet core is cold, do you expect it toIf the planet core is cold, do you expect it tohave magnetic fields?have magnetic fields?

A.A. Yes, refrigerator magnets are cold, andYes, refrigerator magnets are cold, andthey have magnetic fields.they have magnetic fields.

B.B. No, planetary magnetic fields areNo, planetary magnetic fields aregenerated by moving charges around,generated by moving charges around,and if the core is cold, nothing isand if the core is cold, nothing ismoving.moving.


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Special Topic:Special Topic:How do we know whats inside aHow do we know whats inside a

planet?planet?

P wavesP waves

push matterpush matter

back andback andforth.forth.

S wavesS waves

shake mattershake matter

side to side.side to side.


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Special Topic:Special Topic:How do we know whats inside aHow do we know whats inside a

planet?planet? P waves goP waves go

through Earthsthrough Earths

core, but Score, but S

waves do not.waves do not.

We conclude thatWe conclude that

Earths coreEarths core

must have amust have a

liquid outer layer.liquid outer layer.


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What processes shape EarthsWhat processes shape Earths

surface?surface?


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Geological ProcessesGeological Processes

Impact crateringImpact cratering

Impacts by asteroids or cometsImpacts by asteroids or comets

VolcanismVolcanism

Eruption of molten rock onto surfaceEruption of molten rock onto surface

TectonicsTectonics

Disruption of a planets surface by internalDisruption of a planets surface by internalstressesstresses

ErosionErosion

Surface changes made by wind, water, orSurface changes made by wind, water, oriceice


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Impact CrateringImpact Cratering

Most crateringMost crateringhappened soon afterhappened soon afterthe solar systemthe solar systemformed.formed.

Craters are about 10Craters are about 10times wider thantimes wider thanobjects that made them.objects that made them.

Small craters greatlySmall craters greatlyoutnumber large ones.outnumber large ones.

The Production of a Crater


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Impact CratersImpact Craters

Meteor Crater (Arizona)Meteor Crater (Arizona) Tycho (Moon)Tycho (Moon)


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VolcanismVolcanism

Volcanism happensVolcanism happenswhen molten rockwhen molten rock(magma) finds a(magma) finds a

path throughpath throughlithosphere to thelithosphere to thesurface.surface.

Molten rock is calledMolten rock is called

lavalava after it reachesafter it reachesthe surface.the surface.

Volcanic Eruptions and Lava Flows


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Lava and VolcanoesLava and Volcanoes

Runny lava makes flatRunny lava makes flat

lava plains.lava plains.

Slightly thicker lavaSlightly thicker lava

makes broadmakes broadshieldshield

volcanoes.volcanoes.

Thickest lava makesThickest lava makes

steepsteepstratovolcanoes.stratovolcanoes.


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OutgassingOutgassing

Volcanism also releases gases from EarthsVolcanism also releases gases from Earthsinterior into the atmosphere.interior into the atmosphere.


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TectonicsTectonics

Convection of the mantle creates stresses in the crustConvection of the mantle creates stresses in the crustcalled tectonic forces.called tectonic forces.

Compression forces make mountain ranges.Compression forces make mountain ranges.

A valley can form where the crust is pulled apart.A valley can form where the crust is pulled apart.

Tectonics and Convection of the Mantle


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Plate Tectonics on EarthPlate Tectonics on Earth

EarthsEarthscontinents slidecontinents slidearound onaround on

separate platesseparate platesof crust.of crust.

Plate Tectonics on Earth


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ErosionErosion

Erosion is a blanket term for weatherErosion is a blanket term for weather--driven processes that break down ordriven processes that break down ortransport rock.transport rock.

Processes that cause erosion includeProcesses that cause erosion include GlaciersGlaciers

RiversRivers

WindWind


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Erosion by WaterErosion by Water

The ColoradoThe Colorado

RiverRiver

continues tocontinues to

carve thecarve the

GrandGrand

Canyon.Canyon.


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Erosion by IceErosion by Ice

GlaciersGlaciers

carved thecarved the

YosemiteYosemite

Valley.Valley.


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Erosion by WindErosion by Wind

Wind wearsWind wears

away rock andaway rock and

builds up sandbuilds up sand

dunes.dunes.


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Erosional DebrisErosional Debris

Erosion canErosion can

create newcreate new

features byfeatures by

depositingdepositing

debris.debris.


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How does Earths atmosphereHow does Earths atmosphere

affect the planet ?affect the planet ?

Which Molecules are Greenhouse Gases?


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Effects ofAtmosphere on EarthEffects ofAtmosphere on Earth

1.1. ErosionErosion

2.2. Radiation protectionRadiation protection

3.3. Greenhouse effectGreenhouse effect

4.4. Makes the sky blue!Makes the sky blue!


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Radiation ProtectionRadiation Protection

All XAll X--ray light isray light is

absorbed very high inabsorbed very high in

the atmosphere.the atmosphere.

Ultraviolet light isUltraviolet light is

absorbed by ozoneabsorbed by ozone

(O(O33).).


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Earths atmosphere absorbs light at most wavelengths.


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Greenhouse

effect:

Certain

molecules let

sunlight through

but trap escaping

infrared photons.

(H2O, CO2, CH4)

The Green House Effect


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Why is the sky blue?Why is the sky blue?

A.A. The sky reflects light from the oceans.The sky reflects light from the oceans.

B.B. Oxygen atoms are blue.Oxygen atoms are blue.C.C. Nitrogen atoms are blue.Nitrogen atoms are blue.

D.D. Air molecules scatter blue light more than red light.Air molecules scatter blue light more than red light.

E.E. Air molecules absorb red light.Air molecules absorb red light.


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Why is the sky blue?Why is the sky blue?

A.A. The sky reflects light from the oceans.The sky reflects light from the oceans.

B.B.

Oxygen atoms are blue.Oxygen atoms are blue.C.C. Nitrogen atoms are blue.Nitrogen atoms are blue.

D.D. Air molecules scatter blue light more than redAir molecules scatter blue light more than red

light.light.

E.E. Air molecules absorb red light.Air molecules absorb red light.


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A Greenhouse GasA Greenhouse Gas

Any gas that absorbs infraredAny gas that absorbs infrared

Greenhouse gas: molecules with two differentGreenhouse gas: molecules with two different

types of elements (COtypes of elements (CO22, H, H22O, CHO, CH44))

Not a greenhouse gas: molecules with one orNot a greenhouse gas: molecules with one or

two atoms of the same element (Otwo atoms of the same element (O22

, N, N22

))


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Greenhouse Effect: Bad?Greenhouse Effect: Bad?

The Earth is much warmer because of theThe Earth is much warmer because of the

greenhouse effect than it would be withoutgreenhouse effect than it would be without

an atmospherebut so is Venus.an atmospherebut so is Venus.


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Why the sky is blueWhy the sky is blue

Atmosphere scattersAtmosphere scattersblue light from theblue light from theSun, making itSun, making it

appear to come fromappear to come fromdifferent directions.different directions.

Sunsets are redSunsets are redbecause less of thebecause less of thered light from the Sunred light from the Sunis scattered.is scattered.


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Origin of Earths WaterOrigin of Earths Water

Water may haveWater may have

come to Earth bycome to Earth by

way of icyway of icy

planetesimalsplanetesimalsand comets fromand comets from

the outer solarthe outer solar

system.system.


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Summary ofKey IdeasSummary ofKey Ideas


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Earth: A Dynamic, Vital World Earths atmosphere is about fourEarths atmosphere is about four--fifths nitrogen and onefifths nitrogen and one--fifthfifthoxygen.This abundance of oxygen is due to the biologicaloxygen.This abundance of oxygen is due to the biological

processes of lifeprocesses of life--forms on the planet.forms on the planet.

Earths atmosphere is divided into layers named theEarths atmosphere is divided into layers named thetroposphere, stratosphere, mesosphere, and ionosphere.troposphere, stratosphere, mesosphere, and ionosphere.

Ozone molecules in the stratosphere absorb ultraviolet lightOzone molecules in the stratosphere absorb ultraviolet light

rays.rays. The outermost layer, or crust, of Earth offers clues to theThe outermost layer, or crust, of Earth offers clues to the

history of our planet.history of our planet.

Earths surface is divided into huge plates that move over theEarths surface is divided into huge plates that move over theupper mantle. Movement of these plates, a process calledupper mantle. Movement of these plates, a process calledplate tectonics, is caused by convection in the mantle.Also,plate tectonics, is caused by convection in the mantle.Also,

upwelling of molten material along cracks in the ocean floorupwelling of molten material along cracks in the ocean floorproduces seafloor spreading.Plate tectonics is responsible forproduces seafloor spreading.Plate tectonics is responsible formost of the major features of Earths surface, includingmost of the major features of Earths surface, includingmountain ranges, volcanoes, and the shapes of the continentsmountain ranges, volcanoes, and the shapes of the continentsand oceans.and oceans.


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Study of seismic waves (vibrations produced byStudy of seismic waves (vibrations produced byearthquakes) shows that Earth has a small, solid innerearthquakes) shows that Earth has a small, solid innercore surrounded by a liquid outer core.The outer core iscore surrounded by a liquid outer core.The outer core issurrounded by the dense mantle, which in turn issurrounded by the dense mantle, which in turn issurrounded by the thin, lowsurrounded by the thin, low--density crust. Earths innerdensity crust. Earths inner

and outer cores are composed primarily of iron.Theand outer cores are composed primarily of iron.Themantle is composed of ironmantle is composed of iron--rich minerals.rich minerals.

Earths magnetic field produces a magnetosphere thatEarths magnetic field produces a magnetosphere thatsurrounds the planet and blocks the solar wind.surrounds the planet and blocks the solar wind.

Some charged particles from the solar wind are trappedSome charged particles from the solar wind are trapped

in two huge, doughnutin two huge, doughnut--shaped rings called the Van Allenshaped rings called the Van Allenradiation belts.A deluge of particles from a coronal massradiation belts.A deluge of particles from a coronal massejection by the Sun can initiate an auroral display.ejection by the Sun can initiate an auroral display.

Earth: A Dynamic, Vital World


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The Moon and Tides

The Moon has lightThe Moon has light--colored, heavily cratered highlandscolored, heavily cratered highlandsand darkand dark--colored, smoothcolored, smooth--surfaced maria.surfaced maria.

Many lunar rock samples are solidified lava formedMany lunar rock samples are solidified lava formedlargely of minerals also found in Earth rocks.largely of minerals also found in Earth rocks.

Anorthositic rock in the lunar highlands was formedAnorthositic rock in the lunar highlands was formed

between 4.0 and 4.3 billion years ago, whereas the marebetween 4.0 and 4.3 billion years ago, whereas the marebasalts solidified between 3.1 and 3.8 billion years ago.basalts solidified between 3.1 and 3.8 billion years ago.The Moons surface has undergone very little geologicThe Moons surface has undergone very little geologicchange over the past 3 billion years.change over the past 3 billion years.

Impacts have been the only significant weatheringImpacts have been the only significant weatheringagent on the Moon; the Moons regolith (pulverized rockagent on the Moon; the Moons regolith (pulverized rocklayer) was formed by meteoritic action.Lunar rockslayer) was formed by meteoritic action.Lunar rocksbrought back to Earth contain no water and are depletedbrought back to Earth contain no water and are depletedof volatile elements.of volatile elements.

Th M d Tid


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The Moon and Tides

Frozen water may have been discovered at the MoonsFrozen water may have been discovered at the Moonspoles.poles.

The collisionThe collision--ejection theory of the Moons origin,ejection theory of the Moons origin,accepted by most astronomers, holds that the youngaccepted by most astronomers, holds that the youngEarth was struck by a huge asteroid, and debris from thisEarth was struck by a huge asteroid, and debris from thiscollision coalesced to form the Moon.collision coalesced to form the Moon.

The Moon was molten in its early stages, and theThe Moon was molten in its early stages, and theanorthositic crust solidified from lowanorthositic crust solidified from low--density magma thatdensity magma thatfloated to the lunar surface.The mare basins werefloated to the lunar surface.The mare basins werecreated later by the impact of planetesimals and werecreated later by the impact of planetesimals and werethen filled with lava from the lunar interior.then filled with lava from the lunar interior.

Gravitational interactions between Earth and the MoonGravitational interactions between Earth and the Moonproduce tides in the oceans of Earth and set the Moon inproduce tides in the oceans of Earth and set the Moon insynchronous rotation.The Moon is moving away fromsynchronous rotation.The Moon is moving away fromEarth, and, consequently, Earths rotation rate isEarth, and, consequently, Earths rotation rate isdecreasing.decreasing.

Key TermsKey Terms


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Key TermsKey Terms

anorthosite

capture theorycocreation theory

collision-ejection theory

continental drift

convection

core

coronal mass ejectioncrust

dynamo theory

ejecta blanket

fission theory

highlands

impact breccias

ionosphere (thermosphere)

mantle

mare (plural maria)

mare basalt

mascons

mesosphere

neap tidenorthern lights (aurora

borealis)

ozone layer

planetary differentiation

plate tectonics

regolith

rille

seafloor spreading

seismic waves

seismograph

solar wind

southern lights (aurora

australis)spring tide

stratosphere

synchronous rotation

troposphere

VanAllen radiation belts

WHAT DID YOU THINK?


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WHAT DID YOU THINK?

Can Earths ozone layer, which is now being depleted,Can Earths ozone layer, which is now being depleted,

be naturally replenished?be naturally replenished?

Yes. Ozone is created continuously from normal oxygenYes. Ozone is created continuously from normal oxygen

molecules by their interaction with the Suns ultravioletmolecules by their interaction with the Suns ultraviolet

radiation.radiation.

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Who was the first person to walk on the Moon, and whenWho was the first person to walk on the Moon, and when

did this event occur?did this event occur?

Neil Armstrong was the first person to set foot on theNeil Armstrong was the first person to set foot on the

Moon.He and Buzz Aldrin flew on the Apollo 11Moon.He and Buzz Aldrin flew on the Apollo 11

spacecraft piloted by Michael Collins.Armstrong andspacecraft piloted by Michael Collins.Armstrong andAldrin set down the Eagle Lander on the Moon on JulyAldrin set down the Eagle Lander on the Moon on July

20, 1969.20, 1969.

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Do we see all parts of the Moons surface at some timeDo we see all parts of the Moons surface at some time

throughout the lunar cycle of phases?throughout the lunar cycle of phases?

No. Because the Moons rotation around Earth isNo. Because the Moons rotation around Earth is

synchronous, we always see the same side.The far sidesynchronous, we always see the same side.The far side

of the Moon has been seen only from spacecraft thatof the Moon has been seen only from spacecraft thatpass or orbit it.pass or orbit it.

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WHAT DID YOU THINK?

Does the Moon rotate and, if so, how fast?Does the Moon rotate and, if so, how fast?

The Moon rotates at the same rate that it revolvesThe Moon rotates at the same rate that it revolves

around Earth.If the Moon did not rotate, then, as itaround Earth.If the Moon did not rotate, then, as it

revolved, we would see its entire surface from Earth,revolved, we would see its entire surface from Earth,

which we do not.which we do not.

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What causes the ocean tides?What causes the ocean tides?

The tides are created by orbital and gravitational forces,The tides are created by orbital and gravitational forces,

primarily from the Moon and, to a lesser extent, from theprimarily from the Moon and, to a lesser extent, from the

Sun.Sun.

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When does the spring tide occur?When does the spring tide occur?

Spring tides occur twice monthly, during each full andSpring tides occur twice monthly, during each full and

new Moon.new Moon.

discovering the universe earth and moon

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