Hypothesis: Mars had plate tectonics. Last Friday, Oct. 3 Group exercise on Mars Tectonics. 1) Mars had plate tectonics.

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1 Last Friday, Oct. 3 Group exercise on Mars Tectonics Hypothesis: Mars had plate tectonics (google: Mars, plate tectonics; Mars early plate tectonics) Use the images provided, your reading and the web (hints indicated) to argue in favor of ONE of these two. 1) Mars had plate tectonics. 2) Mars did not have plate tectonics. TURN IN: 3 distinct bullets that define your argument. Each bullet can have AT MOST three sentences. Hypothesis: Mars had plate tectonics (google: Mars, plate tectonics; Mars early plate tectonics) Tying things together: Climate-Mantle coupling on Venus (as well as Mars and Earth) Couplings among: -Atmosphere -Hydrosphere -Cryosphere -Lithosphere Can a runaway greenhouse effect kill plate tectonics on Earth? Is a greenhouse runaway one reason why there is no plate tectonics on Venus? 1

2 EARTH (GEOSAT laser altimetry) Earth Atmosphere and surface T Venus Atmosphere and surface T VENUS (MAGELLAN radar altimetry) Climate Concepts: Climate Concepts: -Greenhouse forcing - Volcanic outgassing - Residence time of climate forcings - Weathering cycle - Feedbacks -Greenhouse forcing - Volcanic outgassing - Residence time of climate forcings - Weathering cycle - Feedbacks Atmosphere response to volcanism 2

3 Venus surface temperature in more detail: Volcanism, GH and the sulfur cycle on Venus Bullock and Grinspoon (1998, 2001) Observations and Inferences: Venus in an episodic regime? IC: - ~current temp - atmo in eq. with surface minerals CaCO3 (NOT true currently) Climate Model: Dynamic: -1D radiative/convective -Cloud chem/microphysics Fluxes IN: SO2 and H20 gas flux = 12Gt/yr(t=0)*exp(-λt); λ = 1/10 8 yrs SO2/H2O clouds impossible: Low Albedo, GH Young surface age 80% of the surface is covered in lava Coexistence of dynamically-supported BAT coronae and the highlands --> A transient thermal regime. OUT: -SO2 to surface by SO2 + CaCO3 = CaSO4 + CO e-fold time ~ Myr -H to exosphere e-fold time H2O ~ 160 Myr SO2/H2O clouds: high Albedo SO2 loss=thin H2O clouds, GH Robin, Jellinek, Thayalan, Lenardic, 2007 Onset of plate tectonics on any planet: Keys: Convective stresses and yield stresses Stagnant Lid Convection: One plate planet Some Modeling: Venus as an adolescent planet? Plate tectonics possible τ c < τ yield Cold Drip Can flow into the drip break the plate? Driving Stress (viscous drag) increases with: Flow velocity Mantle viscosity Lid τ yield Restoring Stress Driving Stress τ conv. stress Restoring Stress (critical yield stress) Increases w/ lith thickness Decreases w/ water Increases w/t surf : Depth of serpentinization less Convective stress One Plate Planet Lith. Strength Venus: Possible plate tectonics early. Episodic at present? To which regime will the Venus evolve with GH? 3

4 The Greenhouse runaway on Venus: Planets in transition - Extensive volcanic outgassing - No sink for CO2 - High surface T (now ~ 482 deg C) -How might a transitional regime respond to forcing such as climate change on long time scales (long enough for the mantle to care or order myr)? -What is the effect on Venus of a large increase in surface temperature over the last 500 myr or so due to greenhouse forcing? -What do we learn about climate-mantle coupling on Earth from this exercise? The Greenhouse runaway on Venus: Could it stabilize a stagnant lid regime? A Mantle Thermostat (i.e. boiling point ): Variable viscosity + internal heating + convection Progressive increase Greenhouse Forcing; Increase Tsurface Maintain ΔT for 1 Lith. Response time Q [watts] Plate Tectonics / Active Lid Mode viscosity = A exp(-θt) Teq (Tozer, 1972)) Internal Heating Convective Cooling Tsurf ΔT GH Tcmb Internal Temperature [oc] Stagnant Lid Mode 4

5 Tozer s Mantle Thermostat: enhanced -Variable viscosity and internal heating + -Convective regime Tozer s Mantle Thermostat: enhanced further -Variable viscosity and internal heating + -Convective regime CHANGE via GH Q [watts] T eq (Tozer, 1972)) Internal Heating Convective Cooling viscosity = A exp(-θt) Active lid path Stagnant lid path Q [watts], Convective Stress [Pa] Convective Stress Yield Stress Internal Heating Convective Cooling Active lid path ΔT GH? Active Lid Stagnant Lid Stagnant lid path T surf T cmb T surf T cmb Internal Temperature [ o C] Internal Temperature [ o C] NUMERICAL SIMULATIONS Surface Velocity How to kill plate tectonics on Earth with climate change? Mobile Lithosphere Surface Temperature Change Below Critical Surface Temperature Change above Critical Earth Stays Mobile Goes Stagnant Turn up the surface T by degc. 5

6 What about Venus? SO2/H2O clouds impossible: Low Albedo, GH SO2/H2O clouds: high Albedo SO2 loss=thin H2O clouds, GH Key: Changes occur over and persist for long times (enough time for the mantle to respond) 6