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Lecture 10: Planetary AtmospheresLecture 10: Planetary Atmospheres

Jenn BurtOctober 28th, 2010

Astro 18: Planets and Planetary SystemsUC Santa Cruz

Earth’s atmosphere seen from space

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Topics for TodayTopics for Today

• Part 1: Introduction to Class ProjectsPart 1: Introduction to Class Projects

• Part 2: Lecture on Planetary AtmospheresPart 2: Lecture on Planetary Atmospheres

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Why projects?Why projects?

• Reading, homework, lectures: “content”Reading, homework, lectures: “content”– What we know about our Solar System and others, and the What we know about our Solar System and others, and the

scientific tools used to discover this knowledgescientific tools used to discover this knowledge

• Class Projects: “enterprise of science”Class Projects: “enterprise of science”– The way we The way we reallyreally do science – starting with hunches, making do science – starting with hunches, making

guesses, making many mistakes, going off on blind roads before guesses, making many mistakes, going off on blind roads before hitting on one that seems to be going in the right directionhitting on one that seems to be going in the right direction

• You will choose a general topic. Then you will formulate You will choose a general topic. Then you will formulate your own specific questions about the topic, and figure out your own specific questions about the topic, and figure out a strategy for answering thema strategy for answering them

• We will provide structure via “milestones” along the way, We will provide structure via “milestones” along the way, so you won’t get lostso you won’t get lost

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Projects: Getting startedProjects: Getting started

• Today: Today:

– Brainstorming about potential topicsBrainstorming about potential topics– Topic selectionTopic selection– Group formationGroup formation– First meeting of your groupFirst meeting of your group

• Weekly e-mails to Claire and Jenn from each of you: Weekly e-mails to Claire and Jenn from each of you: how are things going? (be sure to put “Astro18” in how are things going? (be sure to put “Astro18” in subject line)subject line)

• Final project outcomes: last two days of classFinal project outcomes: last two days of class– Presentation in classPresentation in class– Written reportWritten report

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Topics chosen in the past (just a Topics chosen in the past (just a taste of what’s possible)taste of what’s possible)

• Life elsewhere in the universeLife elsewhere in the universe

• Hazards from Outer Space: Killer asteroids and Hazards from Outer Space: Killer asteroids and cometscomets

• New theories of Solar System formationNew theories of Solar System formation

• Global warming on Earth: What’s the evidence? Are Global warming on Earth: What’s the evidence? Are people causing warming? How are predictions made?people causing warming? How are predictions made?

• Were Mars and Venus more hospitable in the past?Were Mars and Venus more hospitable in the past?

• Mars exploration by humans (or by robots)Mars exploration by humans (or by robots)

• Moons of Jupiter and SaturnMoons of Jupiter and Saturn

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First task todayFirst task today

• Brainstorm about potential project topicsBrainstorm about potential project topics

• How to “brainstorm”:How to “brainstorm”:

– One person serves as scribeOne person serves as scribe

– Everyone suggests ideasEveryone suggests ideas

– Scribe writes each one downScribe writes each one down

– No criticisms allowed! Just put all the ideas downNo criticisms allowed! Just put all the ideas down

– Later you’ll decide which questions are most important, most Later you’ll decide which questions are most important, most interesting, etc. DON’T do that now.interesting, etc. DON’T do that now.

• Split into groups of 2 or 3 (your nearest neighbors?)Split into groups of 2 or 3 (your nearest neighbors?)

• Spend 10 minutes brainstorming about project topicsSpend 10 minutes brainstorming about project topics

– Toss around as many questions as you can, write them downToss around as many questions as you can, write them down

– What are you curious about?What are you curious about?

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Brainstorming, continuedBrainstorming, continued

• Main point of brainstorming is to build on each Main point of brainstorming is to build on each others’ ideasothers’ ideas

• Keeping the discussion positive (no criticisms Keeping the discussion positive (no criticisms allowed) encourages creativity.allowed) encourages creativity.– Nobody should feel “turned off” or discouragedNobody should feel “turned off” or discouraged

• Brainstorming a generally useful methodBrainstorming a generally useful method– Used in businesses, arts, as well as scienceUsed in businesses, arts, as well as science

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When 10 minutes have passed, When 10 minutes have passed, we’ll try to categorize the topicswe’ll try to categorize the topics

• Make groupings of related topicsMake groupings of related topics

• Write them on board or on sign-up sheetsWrite them on board or on sign-up sheets

• Ask each of you to sign up for your first choiceAsk each of you to sign up for your first choice

– Include your name and email addressInclude your name and email address

• Form groups for each topic, get together in Form groups for each topic, get together in classclass

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Next task: today in your groupsNext task: today in your groups

• Once you’ve chosen a topic:Once you’ve chosen a topic:

• What specific questions can you ask (and later What specific questions can you ask (and later answer) about your topic?answer) about your topic?

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Example of brainstorming list for Example of brainstorming list for “Pluto” questions“Pluto” questions

• Why is Pluto so small?Why is Pluto so small?

• What is Pluto made of? How do we know?What is Pluto made of? How do we know?

• How come Pluto’s orbit is so elliptical?How come Pluto’s orbit is so elliptical?

• Did Pluto used to be an asteroid? How do we know?Did Pluto used to be an asteroid? How do we know?

• Are there other Plutos?Are there other Plutos?

• Does Pluto have an atmosphere?Does Pluto have an atmosphere?

• What could we learn from sending a spacecraft to Pluto and Charon?What could we learn from sending a spacecraft to Pluto and Charon?

• How long would it take to get there? Could it go into orbit around How long would it take to get there? Could it go into orbit around Pluto?Pluto?

• Does Pluto have seasons? What are they like?Does Pluto have seasons? What are they like?

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Next task: each group work on Next task: each group work on narrowing down your questionsnarrowing down your questions

• Think about which of your questions are most Think about which of your questions are most interesting or importantinteresting or important

• Think about how you would address each one Think about how you would address each one

• Using these criteria, narrow down your list of Using these criteria, narrow down your list of questions to 3 – 5questions to 3 – 5

• Take 10 minutes nowTake 10 minutes now

• Hand in your list at end of class today (be sure to keep Hand in your list at end of class today (be sure to keep copies for yourselves!)copies for yourselves!)

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By Thursday November 4th (1 wk)By Thursday November 4th (1 wk)

• Each group look into their 3-5 questions enough to get an idea:Each group look into their 3-5 questions enough to get an idea:

– Does each question still make sense? Does each question still make sense? – Flesh it out: use reference books (in Science and Flesh it out: use reference books (in Science and

Engineering Library), websites (links on class web page)Engineering Library), websites (links on class web page)– Why is each question important?Why is each question important?– How are they related to each other?How are they related to each other?– What resources are available to address each questionWhat resources are available to address each question

– Textbooks or reference books? Articles in magazines Textbooks or reference books? Articles in magazines such as such as ScienceScience or or Scientific AmericanScientific American or or Sky and Sky and TelescopeTelescope? Websites? Journal articles?? Websites? Journal articles?

– Which group members is most interested in which Which group members is most interested in which questions? questions?

• Each group member sign up to address Each group member sign up to address 1 or 21 or 2 questions questions

• Put “Astro 18” in subject line, send to Put “Astro 18” in subject line, send to max@ucolick.org and to and to jaburt@ucsc.edu

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By Tuesday November 9thBy Tuesday November 9th

• (Group): Together write a 1 - 2 page summary of (Group): Together write a 1 - 2 page summary of what your project is:what your project is:– what are your 3 – 5 questionswhat are your 3 – 5 questions– why are they each important (one by one)why are they each important (one by one)– how are they related to each otherhow are they related to each other– what methods might you use to address themwhat methods might you use to address them

– Books? Articles in magazines such as Science or Books? Articles in magazines such as Science or Scientific American? Websites? Journal articles?Scientific American? Websites? Journal articles?

– What help can Jenn and I give youWhat help can Jenn and I give you

• Put “Astro 18” in subject line, send to Put “Astro 18” in subject line, send to max@ucolick.org and to and to jaburt@ucsc.edu

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By Tuesday November 9th, cont’dBy Tuesday November 9th, cont’d

• From each individual (each of you): email to usFrom each individual (each of you): email to us

– A short email giving me feedback on how your group A short email giving me feedback on how your group is going: did everyone participate in your is going: did everyone participate in your brainstorming session, did you feel included or left brainstorming session, did you feel included or left out, did you enjoy it?out, did you enjoy it?

– Is someone dominating the group too much? Is someone dominating the group too much?

• Are you finding the work interesting? Here’s a place Are you finding the work interesting? Here’s a place to ask advice about sources, etc.to ask advice about sources, etc.

– I’ll ask you to do this each week, for a while at leastI’ll ask you to do this each week, for a while at least

• Put “Astro 18” in subject line, send to Put “Astro 18” in subject line, send to max@ucolick.org and to and to jaburt@ucsc.edu

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Planetary atmospheres: OutlinePlanetary atmospheres: Outline

• What is an atmosphere? What is its structure?What is an atmosphere? What is its structure?

• Temperature of a planet, if the atmosphere Temperature of a planet, if the atmosphere weren’t there (“no-greenhouse temperatures”)weren’t there (“no-greenhouse temperatures”)

• Generic atmospheric structureGeneric atmospheric structure

• Global climate changeGlobal climate change– EarthEarth– VenusVenus– MarsMars

Please remind me to Please remind me to take a break at 12:45 pm!take a break at 12:45 pm!

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The Main PointsThe Main Points

• Planetary atmospheres as a balancing act:Planetary atmospheres as a balancing act:– Gravity vs. thermal motions of air moleculesGravity vs. thermal motions of air molecules– Heating by Sun vs. heat radiated back into spaceHeating by Sun vs. heat radiated back into space– Weather as a way to equalize pressures at different places on a Weather as a way to equalize pressures at different places on a

planet’s surfaceplanet’s surface

• Atmospheres of terrestrial planets are very different now Atmospheres of terrestrial planets are very different now from the way they were bornfrom the way they were born

– Formation: volcanoes, cometsFormation: volcanoes, comets– Destruction: escape, incorporation into rocks, oceansDestruction: escape, incorporation into rocks, oceans– Huge changes over a billion years or lessHuge changes over a billion years or less

• Prospect of human-induced global warming on Earth is a Prospect of human-induced global warming on Earth is a serious issue. Can be approached scientifically.serious issue. Can be approached scientifically.

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Earth’s Atmosphere: Earth’s Atmosphere: Thin blue lineThin blue line

• About 12 km thickAbout 12 km thick

• Earth’s diameter Earth’s diameter 12,000 km, 1000 times 12,000 km, 1000 times biggerbigger

• Consists mostly of Consists mostly of molecular nitrogen molecular nitrogen (N(N22) and oxygen (O) and oxygen (O22))

• Fractions:Fractions:

– 78% Nitrogen78% Nitrogen

– 21% Oxygen21% Oxygen

– 0.04% CO0.04% CO22

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Atmospheric PressureAtmospheric Pressure

Gas Gas pressure pressure depends on depends on both both density and density and temperaturetemperature..

Adding air Adding air molecules molecules increases increases the the pressure in pressure in a balloon.a balloon.

Heating the Heating the air also air also increases increases the the pressure.pressure.

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Atmospheric PressureAtmospheric Pressure

Mathematically: p =nkT. Units: energy per unit volume or force per unit arean=number density (molecules per cubic cm), T =temperature (deg Kelvin), k=Boltzmann constant, Units of kT : energy

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Atmospheric Pressure: Atmospheric Pressure: variation with altitudevariation with altitude

• Pressure and Pressure and density decrease density decrease with altitude with altitude because the weight because the weight of overlying layers is of overlying layers is lessless

• Earth’s pressure at Earth’s pressure at sea level is sea level is – 1.03 kg per sq. meter1.03 kg per sq. meter– 14.7 lbs per sq. inch14.7 lbs per sq. inch– 1 bar1 bar

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In an atmosphere in equilibrium, In an atmosphere in equilibrium, pressure gradient balances gravitypressure gradient balances gravity

Pressure = Net Force / Area

Force =[P(h)−P(h+dh)] ×Area=ΔP×A

Gravitational force=−Mg=− massvolume

⎛⎝⎜

⎞⎠⎟× AΔh( )×g=−ρg×(AΔh)

ΔP×A=−ρg×AΔhΔPΔh

=−ρg or, in calculus language, dPdh

=−ρg

P(h) P(h+Δh)Area A

volume

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Profile of density with altitude Profile of density with altitude (a calculus-based derivation)(a calculus-based derivation)

P =nkT =ρm

⎛⎝⎜

⎞⎠⎟kT

dPdh

=ddh

ρkTm

⎛⎝⎜

⎞⎠⎟=−ρg

If temperature ≈ const, ddh

ρkTm

⎛⎝⎜

⎞⎠⎟=kTm

dρdh

=−ρg

Divide both sides by kTρm

:

1ρdρdh

=−mgkT

=const

Solution: ρ=ρ0e−(h/h0 ) where h0 =

kTmg

h

P

h0

P0 /e

• Pressure, density fall off exponentially with altitudePressure, density fall off exponentially with altitude

• Higher temperature Higher temperature TT larger “scale height” larger “scale height” hh00

• Stronger gravityStronger gravity g g shortershorter “scale height” “scale height” hh00

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How big is pressure scale height?How big is pressure scale height?

• hh00 = kT / mg = kT / mg – height at which pressure has fallen by 1/e = 0.368height at which pressure has fallen by 1/e = 0.368

• Earth Earth hh00 = = 8 km 8 km– the thin blue linethe thin blue line

• VenusVenus hh00 = = 15 km 15 km– ((gg a bit lower, T higher) a bit lower, T higher)

• MarsMars hh00 = = 16 km 16 km– (both g and T lower)(both g and T lower)

Hence the “thin blue line”

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Effects of AtmospheresEffects of Atmospheres

• Create pressure that determines whether liquid Create pressure that determines whether liquid water can exist on surfacewater can exist on surface

• Absorb and scatter lightAbsorb and scatter light

• Create wind, weather, and climateCreate wind, weather, and climate

• Interact with solar wind to create a magnetosphereInteract with solar wind to create a magnetosphere

• Can make planetary surfaces warmer through Can make planetary surfaces warmer through greenhouse effectgreenhouse effect

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Equilibrium atmospheric temperature Equilibrium atmospheric temperature (no atmosphere)(no atmosphere)

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Equilibrium temperature: balance Equilibrium temperature: balance solar heating against coolingsolar heating against cooling

albedo = fraction of sunlight that is albedo = fraction of sunlight that is reflected by a surfacereflected by a surface

Equilibrium or steady state: balance W /m2 = joules/sec per m2

W /m2 absorbed from sunlight = W /m2 emitted in thermal radiation

Scale to Earth: incident power from Sun = 1,360 W m2 at top of atmosphere

1,360 W m2 ×

1 AUdist. from Sun

⎛⎝⎜

⎞⎠⎟

2

×π Rplanet( )2× 1−albedo( ) =σT 4 ×4π Rplanet( )

2

Solve for T:

T =1,360 W /m2 × 1−albedo( )4σ dist. from Sun/1 AU( )2

⎡

⎣⎢⎢

⎤

⎦⎥⎥

1/4

=280K1−albedo

dist. from Sun/1 AU( )2⎡

⎣⎢⎢

⎤

⎦⎥⎥

1/4

“No-greenhouse” temperature

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““No-greenhouse” temperaturesNo-greenhouse” temperatures

• Conclusion: for Venus and Earth, at least, something Conclusion: for Venus and Earth, at least, something else is going on! (not just radiation into space)else is going on! (not just radiation into space)

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Light’s Effects on the AtmosphereLight’s Effects on the Atmosphere

• Ionization: Ionization: Removal of an Removal of an electronelectron

• Dissociation: Dissociation: Destruction Destruction of a molecule of a molecule

• Scattering: Scattering: Change in Change in photon’s directionphoton’s direction

• Absorption: Absorption: Photon’s Photon’s energy is absorbedenergy is absorbed

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How do different energy photons How do different energy photons interact with atmosphere?interact with atmosphere?

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How does the greenhouse effect How does the greenhouse effect warm a planet?warm a planet?

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Greenhouse gasesGreenhouse gases

• carbon dioxide COcarbon dioxide CO22

• water vapor Hwater vapor H2200

• methane CHmethane CH44

• others too (NOothers too (NO22, ....), ....)

• More greenhouse gases in atmosphere can More greenhouse gases in atmosphere can lead to higher surface temperatureslead to higher surface temperatures

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Concept QuestionConcept Question

What would happen to Earth’s temperature if What would happen to Earth’s temperature if Earth’s surface were less reflective?Earth’s surface were less reflective?

a) a) It would go up.It would go up.b) It would go down.b) It would go down.

c) It wouldn’t changec) It wouldn’t change

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Concept QuestionConcept Question

• What would happen to Earth’s temperature if What would happen to Earth’s temperature if Earth’s surface were less reflective?Earth’s surface were less reflective?

a) a) It would go up.It would go up.b) It would go down.b) It would go down.c) It wouldn’t changec) It wouldn’t change

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Melting sea ice lowers reflectivity, Melting sea ice lowers reflectivity, so Earth heats up moreso Earth heats up more

• This is one of the This is one of the factors exacerbating factors exacerbating global warming.global warming.

• As more arctic ice As more arctic ice melts in summer, melts in summer, arctic ocean arctic ocean absorbs more light, absorbs more light, temperature risestemperature rises

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Generic atmospheric structureGeneric atmospheric structure

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Temperature structure of Earth’s Temperature structure of Earth’s atmosphereatmosphere

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Compare Earth, Venus, MarsCompare Earth, Venus, Mars

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History of atmospheres on Venus, History of atmospheres on Venus, Earth, MarsEarth, Mars

• Huge changes took place over the 4.6 billion Huge changes took place over the 4.6 billion years since planets formed!years since planets formed!

• Early atmospheres didn’t resemble current Early atmospheres didn’t resemble current ones at allones at all

• Question: why are atmospheres of Venus, Question: why are atmospheres of Venus, Earth, Mars so different?Earth, Mars so different?

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Sources of atmospheric gasesSources of atmospheric gases

Outgassing Outgassing from from volcanoesvolcanoes

Evaporation Evaporation of surface of surface liquid; liquid; sublimation sublimation of surface of surface iceice

Impacts of Impacts of particles particles and photons and photons eject small eject small amountsamounts

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Kilauea volcano outgassingKilauea volcano outgassing

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Losses of Atmospheric GasesLosses of Atmospheric Gases

CondensatioCondensation onto n onto surfacesurface

Chemical Chemical reactions reactions with with surfacesurface

Large Large impacts impacts blast gas blast gas into spaceinto space

Thermal escape Thermal escape of atomsof atoms

Sweeping by Sweeping by solar windsolar wind

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Thermal Escape of atmospheric gasesThermal Escape of atmospheric gases

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Components of atmospheres on Components of atmospheres on Venus, Earth, MarsVenus, Earth, Mars

• Why are they so different?Why are they so different?

• Were they always this different from each other?Were they always this different from each other?

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The three atmospheres of Earth:The three atmospheres of Earth:“First Atmosphere”“First Atmosphere”

• First Atmosphere: Primordial elements

– Composition - Probably H2, He

• Today these gases are relatively rare on Earth compared to other places in the universe.

• Were probably lost to space early in Earth's history because

– Earth's gravity is not strong enough to hold lightest gases– Earth still did not have a differentiated core (solid inner/liquid

outer core) which creates Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar wind. Magnetosphere protects any atmosphere from the solar wind.

• Once the core differentiated, gases could be retained.

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““Second atmosphere”: produced Second atmosphere”: produced by volcanic outgassingby volcanic outgassing

• Gases similar to those from modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane)

• No free oxygen (O2 not found in volcanic gases)

• Ocean Formation - As Earth cooled, H2O produced by outgassing could exist as liquid

• CO2 could then dissolve in ocean, be sequestered in marine sediments

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““Third atmosphere”: Third atmosphere”: Free oxygen, lower COFree oxygen, lower CO22

• Today, atmosphere is ~21% free oxygen. How did oxygen reach this level?

• Oxygen Production– Photochemical dissociation - breakup of water molecules by ultraviolet light

» Produced O2 levels 1-2% current levels

» At these levels O3 (Ozone) could form to shield Earth surface from UV

– Photosynthesis: CO2 + H2O + sunlight = organic compounds + O2 - Supplied the rest of O2 to atmosphere.

• Oxygen Consumers– Chemical Weathering - through oxidation of surface materials (early consumer)– Respiration of plants and animals (much later)– Burning of Fossil Fuels (much, much later)

• Once rocks at the surface were sufficiently oxidized, more oxygen could remain free in the atmosphere

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Why does Earth’s climate stay Why does Earth’s climate stay relatively stable?relatively stable?

1.1. Atmospheric COAtmospheric CO22 dissolves in dissolves in rainwaterrainwater

2.2. Rain erodes Rain erodes minerals which flow minerals which flow into oceaninto ocean

3.3. Minerals combine Minerals combine with carbon to make with carbon to make rocks on ocean floorrocks on ocean floor

The Carbon Dioxide Cycle

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4.4. Subduction carries Subduction carries carbonate rocks down carbonate rocks down into mantleinto mantle

5.5. Rocks melt in mantle Rocks melt in mantle and outgas COand outgas CO22 back back into atmosphere into atmosphere through volcanoesthrough volcanoes

6.6. Note that Plate Note that Plate Tectonics is essential Tectonics is essential component of this component of this cyclecycle

Why does Earth’s climate stay Why does Earth’s climate stay relatively stable?relatively stable?

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Earth’s ThermostatEarth’s Thermostat

• Cooling allows COCooling allows CO22 to build up in atmosphere to build up in atmosphere

• Heating causes rain to reduce COHeating causes rain to reduce CO2 2 in atmospherein atmosphere

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Cyanobacteria and stromatolites Cyanobacteria and stromatolites made early oxygen for atmospheremade early oxygen for atmosphere

• The first photosynthesisThe first photosynthesis

– Consumes COConsumes CO22, release O, release O22

Cyanobacteria: colonies are called stromatolitesCyanobacteria: colonies are called stromatolites

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Earth: hydrological cycleEarth: hydrological cycle

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Did Earth get its water from Did Earth get its water from comets?comets?

• Some water from outgassing volcanoesSome water from outgassing volcanoes

• Second potential source of the Earth's ocean water is Second potential source of the Earth's ocean water is comet-like balls of ice.comet-like balls of ice.

• Enter atmosphere at rate of about 20/second.Enter atmosphere at rate of about 20/second.

• Four billion years of such bombardment would give Four billion years of such bombardment would give enough water to fill the oceans to their present enough water to fill the oceans to their present volume.volume.

• Possible problems: isotope ratios don’t match. Possible problems: isotope ratios don’t match. Under active research.Under active research.

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What factors can cause long-term What factors can cause long-term climate change?climate change?

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Solar BrighteningSolar Brightening

• Sun very gradually grows brighter with time, Sun very gradually grows brighter with time, increasing the amount of sunlight warming planetsincreasing the amount of sunlight warming planets

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Changes in Axis TiltChanges in Axis Tilt

• Greater tilt makes more extreme seasons, while Greater tilt makes more extreme seasons, while smaller tilt keeps polar regions coldersmaller tilt keeps polar regions colder

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Changes in ReflectivityChanges in Reflectivity

• Higher reflectivity tends to cool a planet, while Higher reflectivity tends to cool a planet, while lower reflectivity leads to warminglower reflectivity leads to warming

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Changes in Greenhouse GasesChanges in Greenhouse Gases

• Increase in greenhouse gases leads to warming, Increase in greenhouse gases leads to warming, while a decrease leads to coolingwhile a decrease leads to cooling

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Global Warming on EarthGlobal Warming on Earth

• Global temperatures have tracked COGlobal temperatures have tracked CO22 concentration concentration for last 500,000 yearsfor last 500,000 years

• Antarctic air bubbles indicate current COAntarctic air bubbles indicate current CO22 concentration is highest in at least 500,000 yearsconcentration is highest in at least 500,000 years

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Intergovernmental Panel on Intergovernmental Panel on Climate Change (IPCC)Climate Change (IPCC)

• International scientific consensusInternational scientific consensus

– The majority of atmospheric scientists agreeThe majority of atmospheric scientists agree– A few do not agreeA few do not agree

• Series of important reports based on scientific Series of important reports based on scientific method (not infallible, but high quality)method (not infallible, but high quality)

• Nobel Peace PrizeNobel Peace Prize

• Look for yourselves: Good website Look for yourselves: Good website http://www.ipcc.ch/

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IPCC Report 2007

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Global mean surface Global mean surface temperatures have increasedtemperatures have increased

IPCC Report 2007

Glaciers and frozen ground are recedingGlaciers and frozen ground are receding

Area of seasonally frozen Area of seasonally frozen ground in NH has decreasedground in NH has decreasedby 7% from 1901 to 2002by 7% from 1901 to 2002

Increased Glacier retreat Increased Glacier retreat since the early 1990ssince the early 1990s

IPCC Report 2007

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The Chacaltaya Glacier The Chacaltaya Glacier and Ski Lift, Boliviaand Ski Lift, Bolivia

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Global temperature will keep rising Global temperature will keep rising even after COeven after CO22 emissionsemissions are reduced are reduced

IPCC Report 2007

Once COOnce CO22 gets into atmosphere, it stays there for hundreds of years! gets into atmosphere, it stays there for hundreds of years!Once COOnce CO22 gets into atmosphere, it stays there for hundreds of years! gets into atmosphere, it stays there for hundreds of years!

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IPCC Report 2007

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The greenhouse effect: The greenhouse effect: What about Venus and Mars?What about Venus and Mars?

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Venus ClimateVenus Climate

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Venus tectonicsVenus tectonics

• No evidence for No evidence for plateplate tectonics on Venustectonics on Venus

– No mid-ocean riftsNo mid-ocean rifts– No subduction trenchesNo subduction trenches

• Volcanos spread Volcanos spread evenlyevenly across surface instead of at across surface instead of at plate boundaries, as on plate boundaries, as on Earth. Earth.

• Lithosphere not broken into Lithosphere not broken into plates; probably because plates; probably because heat at surface slightly heat at surface slightly softens the lithosphere.softens the lithosphere.

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No carbon-silicate cycle on VenusNo carbon-silicate cycle on Venus

Earth’s Earth’s carbon-carbon-silicate cyclesilicate cycle

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Resurfacing on VenusResurfacing on Venus

• Venus has far fewer impact craters than Moon & Mercury, but more Venus has far fewer impact craters than Moon & Mercury, but more than Earth (dense atmosphere protects it)than Earth (dense atmosphere protects it)

• Geologic activity (volcanic resurfacing) has erased most small Geologic activity (volcanic resurfacing) has erased most small craterscraters

• Surface age is only about a billion years.Surface age is only about a billion years.

• Rather uniform age implies that Venus was "resurfaced" by lava Rather uniform age implies that Venus was "resurfaced" by lava flows during a recent, relatively short periodflows during a recent, relatively short period

• This differs profoundly from Earth's crustal history. What is it This differs profoundly from Earth's crustal history. What is it telling us?telling us?

– Could Venus' present crust only have formed that recently?Could Venus' present crust only have formed that recently?– Could there have been a growing crust before 1 billion years ago that Could there have been a growing crust before 1 billion years ago that

"turned over" as heat built up underneath, to lead to a new era of major "turned over" as heat built up underneath, to lead to a new era of major lava flows?lava flows?

– Why?Why?

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There was once liquid water on There was once liquid water on MarsMars

• Geomorphological evidence (*lots* of it)Geomorphological evidence (*lots* of it)– River and flood channels, alluvial fans, slumps, canyons, ...River and flood channels, alluvial fans, slumps, canyons, ...

• One more piece of evidence: shape of ocean basinsOne more piece of evidence: shape of ocean basins

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Why did Mars’ climate change?Why did Mars’ climate change?

• Evidence of previous era Evidence of previous era when liquid water was when liquid water was plentifulplentiful

• Today: Evidence for ice Today: Evidence for ice mixed with soil in top mixed with soil in top meter of groundmeter of ground

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Climate Change on MarsClimate Change on Mars

• Mars has not had Mars has not had widespread surface widespread surface water for 3 billion water for 3 billion yearsyears

• Greenhouse effect Greenhouse effect probably kept probably kept surface warmer surface warmer before thatbefore that

• Somehow Mars lost Somehow Mars lost most of its most of its atmosphere (no atmosphere (no more Greenhouse)more Greenhouse)

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Mars’ atmosphere affected byMars’ atmosphere affected byboth volcanoes and B fields?both volcanoes and B fields?

• Shortly after Mars formed, its surface temperature was ~ equal to its Shortly after Mars formed, its surface temperature was ~ equal to its blackbody temperature (around -55 C).blackbody temperature (around -55 C).

• As volcanoes dumped COAs volcanoes dumped CO22 and H and H22O vapor into atmosphere, greenhouse effect O vapor into atmosphere, greenhouse effect

increased temperature above 0 C (freezing) so liquid water could exist.increased temperature above 0 C (freezing) so liquid water could exist.

• Two competing effects determined amount of COTwo competing effects determined amount of CO22 in atmosphere: volcanoes in atmosphere: volcanoes

adding COadding CO22, and rocks absorbing CO, and rocks absorbing CO22. Result: moderate level of CO. Result: moderate level of CO22 . .

• Greenhouse effect could keep surface T > 0 C, as long as volcanoes kept Greenhouse effect could keep surface T > 0 C, as long as volcanoes kept erupting.erupting.

• Eventually Mars' core cooled and solidified (Mars is small). Volcanic activity Eventually Mars' core cooled and solidified (Mars is small). Volcanic activity subsided. Magnetic field went away, solar wind particles eroded atmosphere.subsided. Magnetic field went away, solar wind particles eroded atmosphere.

• Once rate of eruptions tapered off, COOnce rate of eruptions tapered off, CO22 in the atmosphere started to fall. in the atmosphere started to fall.

• As the atmosphere thinned out, the greenhouse effect weakened. Eventually As the atmosphere thinned out, the greenhouse effect weakened. Eventually the average surface temperature dropped, and surface water froze.the average surface temperature dropped, and surface water froze.

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The Main PointsThe Main Points

• Planetary atmospheres are a balancing act:Planetary atmospheres are a balancing act:– Gravity vs. thermal motions of air moleculesGravity vs. thermal motions of air molecules– Heating by Sun vs. heat radiated back into spaceHeating by Sun vs. heat radiated back into space– Weather as a way to equalize pressures at different places on Weather as a way to equalize pressures at different places on

Earth’s surfaceEarth’s surface

• Atmospheres of terrestrial planets are very different now Atmospheres of terrestrial planets are very different now from the way they were bornfrom the way they were born

– Formation: volcanoes, cometsFormation: volcanoes, comets– Destruction: escape, incorporation into rocks, oceansDestruction: escape, incorporation into rocks, oceans– Huge changes over a billion years or lessHuge changes over a billion years or less

• Prospect of human-induced global warming on Earth Prospect of human-induced global warming on Earth needs to be taken seriouslyneeds to be taken seriously