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Last Friday, Oct. 3 Group exercise onMars’ Tectonics

Use the images provided, your reading and theweb (hints indicated) to argue in favor of ONEof these two.

1) Mars had plate tectonics.

2) Mars did not have platetectonics.

TURN IN: 3 distinct bullets that defineyour argument. Each bullet can have ATMOST three sentences.

Hypothesis: Mars had plate tectonics(google: Mars, plate tectonics; Mars early plate tectonics)

Hypothesis: Mars had plate tectonics(google: Mars, plate tectonics; Mars early plate tectonics)

Can a runaway greenhouse effect killplate tectonics on Earth?

Is a greenhouse runaway one reasonwhy there is no plate tectonics onVenus?

Tying things together:Climate-Mantle coupling on Venus

(as well as Mars and Earth)

Couplings among:-Atmosphere-Hydrosphere-Cryosphere -Lithosphere

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EARTH(GEOSAT

laser altimetry)

VENUS(MAGELLAN radar

altimetry)

Earth Atmosphere and surface T

Venus Atmosphere and surface T

ClimateConcepts:-Greenhouse forcing- Volcanic outgassing- Residence time ofclimate forcings- Weathering cycle- Feedbacks

Atmosphere response to volcanism

ClimateConcepts:-Greenhouse forcing- Volcanic outgassing- Residence time ofclimate forcings- Weathering cycle- Feedbacks

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Venus surface temperature in more detail:Volcanism, GH and the sulfur cycle on Venus

IC:- ~current temp- atmo in eq. with surfaceminerals CaCO3(NOT true currently)

Climate Model:Dynamic:-1D radiative/convective-Cloud chem/microphysics

FluxesIN:SO2 and H20 gas flux =12Gt/yr(t=0)*exp(-λt);λ = 1/108 yrs

OUT:-SO2 to surface bySO2 + CaCO3 = CaSO4 + COe-fold time ~ 20-50 Myr-H to exospheree-fold time H2O ~ 160 Myr

Bullock and Grinspoon (1998, 2001)

SO2 loss=thin H2Oclouds, GH

SO2/H2O clouds impossible:

Low Albedo, GH

SO2/H2O clouds: high Albedo

Observations and Inferences:Venus in an episodic regime?

• Young surface age

• 80% of the surface is covered in lava

• Coexistence of dynamically-supported BATcoronae and the highlands --> A transientthermal regime.

Robin, Jellinek, Thayalan, Lenardic, 2007

Onset of plate tectonics on any planet: Keys: Convective stresses and yield stresses

Stagnant Lid Convection: One plate planet

Driving Stress(viscous drag)increases with:• Flow velocity• Mantle viscosity

Restoring Stress(critical yield stress)

• Increases w/ lith thickness• Decreases w/ water• Increases w/Tsurf: Depthof serpentinization less

Cold Drip

Lid

Can flow into thedrip break the plate?

τc < τyield

DrivingStress

RestoringStress

τconv. stress

τyield

Some Modeling:Venus as an adolescent planet…?

Venus:• Possible plate tectonics early.• Episodic at present?• To which regime will the Venus evolve with GH?

Conv

ecti

ve s

tres

s

Lith. Strength

Plate tectonics possible

One Plate Planet

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Planets in transition…

-How might a transitional regime respond toforcing such as climate change on long timescales (long enough for the mantle to “care”or order 10-100 myr)?

-What is the effect on Venus of a largeincrease in surface temperature over the last500 myr or so due to greenhouse forcing?

-What do we learn about climate-mantlecoupling on Earth from this exercise?

The Greenhouse “runaway” on Venus: - Extensive volcanic outgassing - No sink for CO2- High surface T (now ~ 482 deg C)

The Greenhouse “runaway” on Venus:Could it stabilize a stagnant lid regime?

Progressive increaseGreenhouse Forcing;Increase Tsurface

Maintain ΔT for 1Lith. Response time

Plate Tectonics /Active Lid Mode

Stagnant Lid Mode

Q [wa

tts]

Internal Heating(constant)

Convective Cooling

Internal Temperature [oC]

viscosity = A exp(-θT)

Tsurf Tcmb

Teq (Tozer, 1972))

A Mantle Thermostat (i.e. “boiling point”):Variable viscosity + internal heating + convection

ΔTGH

5

Tozer’s Mantle Thermostat: enhanced

-Variable viscosity and internal heating+-Convective regime

Q [wa

tts]

Internal Heating(constant)

Convective Cooling

Active lid path

Stagnant lid path

Internal Temperature [oC]

viscosity = A exp(-θT)

Tsurf Tcmb

Teq (Tozer, 1972))

Q [wa

tts]

, C

onve

ctive

Str

ess

[Pa]

Internal Heating(constant)

Convective Cooling

Active lid path

Stagnant lid path

Internal Temperature [oC]

Convective StressYield Stress(constant)

Active LidStagnant Lid

Tsurf Tcmb

Tozer’s Mantle Thermostat: enhanced further

-Variable viscosity and internal heating+-Convective regime CHANGE via GH

ΔTGH

?

NUMERICAL SIMULATIONS

Surface Temperature Change above Critical

Mobile Lithosphere

Stays Mobile Goes Stagnant

Surface Velocity

Surface Temperature Change Below Critical

How to kill plate tectonics on Earthwith climate change?

Earth

Turn up the surface T by 50-100 degC….

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SO2 loss=thin H2Oclouds, GH

SO2/H2O clouds impossible:

Low Albedo, GH

SO2/H2O clouds: high Albedo

What about Venus?

Key: Changes occur over and persistfor long times (enough time for themantle to respond)